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Or photographic latitude photographic material is the ratio between the maximum and minimum exposure values \u200b\u200bthat can be correctly captured in the picture. When applied to digital photography, the dynamic range is actually equivalent to the ratio of the maximum and minimum possible values \u200b\u200bof the useful electrical signal generated by the photosensor during exposure.

Dynamic range is measured in exposure stops (). Each step corresponds to doubling the amount of light. So, for example, if a certain camera has a dynamic range of 8 EV, then this means that the maximum possible value of the useful signal of its matrix is \u200b\u200brelated to the minimum as 2 8: 1, which means that the camera is able to capture objects that differ in brightness within one frame. no more than 256 times. More precisely, it can capture objects with any brightness, however, objects whose brightness will exceed the maximum permissible value will appear dazzling white in the picture, and objects whose brightness will be below the minimum value - coal black. Details and texture will be discernible only on those objects, the brightness of which is within the dynamic range of the camera.

To describe the relationship between the brightness of the lightest and the darkest of the objects being shot, the incorrect term "scene dynamic range" is often used. It would be more correct to talk about the brightness range or the contrast level, since the dynamic range is usually a characteristic of the measuring device (in this case, the matrix of a digital camera).

Unfortunately, the brightness range of many of the beautiful scenes we encounter in real life can significantly exceed the dynamic range of a digital camera. In such cases, the photographer is forced to decide which objects should be worked out in full detail, and which can be left outside the dynamic range without compromising the creative idea. In order to make the most of the dynamic range of your camera, sometimes you may need to develop an artistic flair rather than a thorough understanding of how the sensor works.

Dynamic range limiting factors

The lower limit of the dynamic range is set by the noise level of the photosensor. Even an unlit matrix generates a background electrical signal called dark noise. Also, interference occurs when the charge is transferred to the analog-to-digital converter, and the ADC itself introduces a certain error into the digitized signal - the so-called. sampling noise.

If you take a picture in complete darkness or with a lens cap, the camera will only record this meaningless noise. If you allow a minimum amount of light to hit the sensor, the photodiodes will begin to build up an electrical charge. The amount of charge, and hence the intensity of the useful signal, will be proportional to the number of captured photons. In order to show at least some meaningful detail in the picture, it is necessary that the level of the useful signal exceeds the level of background noise.

Thus, the lower limit of the dynamic range, or, in other words, the sensitivity threshold of the sensor, can formally be defined as the level of the output signal at which the signal-to-noise ratio is greater than unity.

The upper limit of the dynamic range is determined by the capacitance of an individual photodiode. If, during exposure, any photodiode accumulates an electric charge of a maximum value for itself, then the image pixel corresponding to the overloaded photodiode will turn out to be absolutely white, and further irradiation will not affect its brightness in any way. This phenomenon is called clipping. The higher the overload capacity of the photodiode, the more signal it can give at the output before it reaches saturation.

For clarity, let's turn to the characteristic curve, which is a graph of the dependence of the output signal on exposure. The horizontal axis represents the binary logarithm of the radiation received by the sensor, and the vertical axis represents the binary logarithm of the electrical signal generated by the sensor in response to this radiation. My drawing is largely arbitrary and for illustrative purposes only. The characteristic curve of a real photosensor has a slightly more complex shape, and the noise level is rarely so high.

The graph clearly shows two critical breaking points: in the first of them, the level of the useful signal crosses the noise threshold, and in the second, the photodiodes reach saturation. Exposure values \u200b\u200blying between these two points make up the dynamic range. In this abstract example, it is equal, as is easy to see, 5 EV, i.e. the camera can handle five doubles of exposure, which is equivalent to a 32x (2 5 \u003d 32) difference in brightness.

The exposure zones that make up the dynamic range are not equal. The upper zones have a higher signal-to-noise ratio and therefore appear cleaner and more detailed than the lower ones. As a result, the upper limit of the dynamic range is very substantial and tangible - clipping cuts off light at the slightest overexposure, while the lower limit imperceptibly drowns in noise, and the transition to black is far from being as sharp as to white.

The linear dependence of the signal on the exposure, as well as the sharp reaching a plateau, are unique features of the digital photographic process. For comparison, take a look at the conventional characteristic curve of traditional photographic film.

The shape of the curve and especially the angle of inclination strongly depend on the type of film and the procedure for its development, but the main thing, striking difference between the film schedule and the digital one, remains unchanged - the nonlinear nature of the dependence of the optical density of the film on the exposure value.

The lower limit of the photographic latitude of the negative film is determined by the density of the veil, and the upper limit is determined by the maximum achievable optical density of the photo layer; for reversible films, the opposite is true. Both in the shadows and in the highlights, smooth curves of the characteristic curve are observed, indicating a drop in contrast when approaching the boundaries of the dynamic range, because the slope of the curve is proportional to the image contrast. Thus, the exposure zones located in the middle of the graph have the maximum contrast, while the contrast is reduced in the highlights and shadows. In practice, the difference between film and digital matrix is \u200b\u200bespecially noticeable in highlights: where in a digital image the lights are burned out by clipping, on the film the details are still distinguishable, albeit low-contrast, and the transition to pure white looks smooth and natural.

In sensitometry, even two independent terms are used: photographic latitudelimited by a relatively linear portion of the characteristic curve, and useful photographic latitude, including, in addition to the linear section, also the base and the leverage of the chart

It is noteworthy that when processing digital photographs, as a rule, a more or less pronounced S-shaped curve is applied to them, increasing the contrast in midtones at the cost of reducing it in shadows and highlights, which makes the digital image more natural and pleasing to the eye.

Bit depth

Unlike the matrix of a digital camera, human vision is characterized by, let's say, a logarithmic view of the world. Successive doubling of the amount of light is perceived by us as equal changes in brightness. Light numbers can even be compared with musical octaves, because two-fold changes in the frequency of sound are perceived by ear as a single musical interval. Other senses work according to this principle. Nonlinearity of perception greatly expands the range of a person's sensitivity to stimuli of varying intensity.

When converting a RAW file (it does not matter - by means of a camera or in a RAW converter) containing linear data, the so-called. gamma curve, which is designed to non-linearly increase the brightness of a digital image, bringing it in line with the characteristics of human vision.

With linear conversion, the image is too dark.

After gamma correction, the brightness returns to normal.

The gamma curve stretches the dark tones and compresses the light ones, making the distribution of gradations more even. As a result, the image looks natural, but noise and sampling artifacts in the shadows inevitably become more noticeable, which is only exacerbated by the small number of brightness levels in the lower zones.

Linear distribution of brightness gradations.

Even distribution after applying the gamma curve.

ISO and dynamic range

Despite the fact that digital photography uses the same concept of photosensitivity of photographic material as in film photography, it should be understood that this happens solely by virtue of tradition, since the approaches to changing photosensitivity in digital and film photography differ fundamentally.

Increasing ISO sensitivity in traditional photography means replacing one film with another with a larger grain, i.e. there is an objective change in the properties of the photographic material itself. In a digital camera, the light sensitivity of the sensor is rigidly determined by its physical characteristics and cannot be literally changed. When the ISO is raised, the camera does not change the actual sensitivity of the sensor, but only amplifies the electrical signal generated by the sensor in response to radiation and adjusts the algorithm for digitizing this signal accordingly.

An important consequence of this is the reduction in effective dynamic range in proportion to the increase in ISO, because along with the useful signal, noise also increases. If at ISO 100 the entire range of signal values \u200b\u200bis digitized - from zero to the saturation point, then at ISO 200 only half of the photodiode capacity is taken as the maximum. With each doubling of ISO sensitivity, the upper stop of the dynamic range is cut off, and the remaining stops are pulled up in its place. That is why using ultra-high ISO values \u200b\u200bis not practical. You might as well lighten a photo in a RAW converter and get comparable noise levels. The difference between raising the ISO and artificially brightening the image is that when the ISO is raised, the signal is amplified before it enters the ADC, which means that the quantization noise is not amplified, unlike the intrinsic noise of the sensor, while in the RAW converter it is amplified including ADC errors. In addition, reducing the sampling range means more accurate sampling of the remaining input signal values.

By the way, lowering the ISO below the base value (for example, to ISO 50), available on some devices, does not expand the dynamic range at all, but simply attenuates the signal by half, which is equivalent to darkening the picture in a RAW converter. This feature can even be viewed as detrimental, since using a sub-minimum ISO setting causes the camera to increase exposure, which, if the sensor saturation threshold remains unchanged, increases the risk of clipping in highlights.

True dynamic range value

There are a number of programs like (DxO Analyzer, Imatest, RawDigger, etc.) that allow you to measure the dynamic range of a digital camera at home. In principle, this is not really necessary, since data for most cameras can be freely found on the Internet, for example, on the DxOMark.com website.

Should we believe the results of such tests? Quite. With the only proviso that all these tests determine the effective or, if I may say so, the technical dynamic range, i.e. the relationship between the saturation level and the matrix noise level. For the photographer, the first thing that is important is the useful dynamic range, i.e. the number of exposure zones that really allow you to capture some useful information.

Remember, the dynamic range threshold is set by the noise level of the photosensor. The problem is that in practice the lower zones, which are formally already included in the dynamic range, still contain too much noise to be used effectively. Much depends on individual disgust - everyone determines the acceptable noise level for himself.

My subjective opinion is that the details in the shadows start to look more or less decent with a signal-to-noise ratio of at least eight. On this basis, I define my useful dynamic range as technical dynamic range minus approximately three stops.

For example, if a DSLR camera, according to reliable tests, has a dynamic range of 13 EV, which is very good by today's standards, then its useful dynamic range will be about 10 EV, which, in general, is also quite good. Of course, we are talking about shooting in RAW, with a minimum ISO and maximum bit depth. When shooting in JPEG, the dynamic range is highly dependent on the contrast settings, but on average, two or three stops should be dropped.

For comparison: color reversible photographic films have a useful photographic latitude of 5-6 stops; black and white negative films give 9-10 steps with standard development and printing procedures, and with certain manipulations - up to 16-18 steps.

Summing up the above, let's try to formulate several simple rules, following which will help you squeeze the maximum performance out of your camera sensor:

• The dynamic range of a digital camera is fully available only when shooting in RAW.
• Dynamic range decreases with increasing ISO, so avoid high ISO values \u200b\u200bunless absolutely necessary.
• Using a higher bit depth for RAW files does not increase the true dynamic range, but it does improve tonal separation in shadows at the expense of more brightness levels.
• Exposure to the right. The upper exposure zones always contain the maximum of useful information with the minimum of noise and should be used most effectively. At the same time, do not forget about the danger of clipping - pixels that have reached saturation are absolutely useless.

Best of all, don't worry too much about your camera's dynamic range. She's fine with dynamic range. Your ability to see light and control exposure is much more important. A good photographer will not complain about the lack of photographic latitude, but will try to wait for more comfortable lighting, or change the angle, or use the flash, in a word, will act according to the circumstances. I'll tell you more: some scenes only benefit from the fact that they do not fit into the dynamic range of the camera. Often an unnecessary abundance of details simply needs to be hidden in a semi-abstract black silhouette, which makes the photo both laconic and richer.

High contrast is not always bad - you just need to know how to work with it. Learn to exploit the disadvantages of the equipment as well as its merits, and you will be amazed at how much your creativity will expand.

Thanks for your attention!

Vasily A.

Post scriptum

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Home audio enthusiasts exhibit an interesting paradox. They are ready to shovel the listening room, build speakers with exotic emitters, but embarrassedly retreat in front of musical canned food, like a wolf in front of a red flag. But in fact, why is it impossible to step behind the flag, and try to cook something more edible from canned food?

From time to time on the forum there are complaining questions: "Please advise well-recorded albums." This is understandable. Although special audiophile editions will please the ear for the first minute, no one listens to them until the end, the repertoire is too dull. As for the rest of the library, the problem seems to be obvious. You can save, but you can not save and pour a lot of money into components. Anyway, few people like to listen to their favorite music at high volume and the capabilities of the amplifier have nothing to do with it.

Today, even in Hi-Res albums, the peaks of the phonogram are cut off and the volume is driven into clipping. It is believed that the majority listens to music on all sorts of junk, and therefore it is necessary to "turn on the gas", to make a kind of loudness.

Of course, this is not done on purpose to upset audiophiles. Few people remember about them. But they only guessed to shave them off master files from which the main circulation is copied - CDs, MP3s and so on. Of course, the master has long been flattened by the compressor, no one will deliberately prepare special versions for HD Tracks. Unless a certain procedure is followed for vinyl media, which for this reason sounds more humane. And for the digital path, it all ends the same - with a big fat compressor.

So, at the present time all 100% of the published phonograms, excluding classical music, are compressed during mastering. Someone performs this procedure more or less skillfully, and someone is completely stupid. As a result, we have pilgrims on the forums with the DR plugin line in their bosom, painful comparisons of publications, escape to vinyl, where the first press also needs to be mined.

The most frostbitten at the sight of all these outrages literally turned into audio Satanists. No kidding, they read sound engineering scripture backwards! Modern sound editing programs have some kind of restoration tool for the clipped sound wave.

This functionality was originally intended for studios. When mixing, there are situations when the clipping is on the recording, and it is no longer possible to remake the session for a number of reasons, and here the arsenal of an audio editor comes to the rescue - a declipper, a decompressor, etc.

And now ordinary listeners who are bleeding from their ears after the next novelty are more and more boldly pulling their pens to such software. Someone prefers iZotope, someone Adobe Audition, someone shares operations between several programs. The point of restoring the previous dynamics is to programmatically correct clipped signal peaks, which, resting at 0 dB, resemble a gear.

Yes, there is no question of 100% revival of the source, since interpolation processes take place according to rather speculative algorithms. Still, some of the processing results seemed to me interesting and worthy of study.

For example, Lana Del Rey's album "Lust For Life", consistently swearing, ugh, mastering! The original song "When the World Was at War We Kept Dancing" was like this.

And after a series of declippers and decompressors it became like this. The DR coefficient has changed from 5 to 9. You can download and listen to the sample before and after processing.

I can't say that the method is universal and suitable for all ditched albums, but in this case I preferred to keep in the collection this very version, processed by a root tracker activist, instead of the official 24-bit edition.

Even if artificially pulling peaks out of the sounding stuffing doesn't bring back the true dynamics of the musical performance, your DAC will still thank you. It was so hard for him to work without errors at extreme levels, where there is a high probability of the so-called inter-sample peaks (ISP). And now only rare flashes of the signal will jump to 0 dB. In addition, the muted phonogram when compressed in FLAC or other lossless codec will now be smaller in size. More "air" in the signal saves hard drive space.

Try to bring your most hated albums killed in the loudness war to life. For headroom, you first need to lower the track level by -6 dB and then start the declipper. Those who don't believe in computers can simply stick a studio expander between the CD player and the amplifier. This device essentially does the same thing — how it can reconstruct and stretch the peaks of a dynamically compressed audio signal. Such devices from the 80s-90s are worth not to say that they are very expensive, and as an experiment it will be very interesting to try them.

Dynamic range controller DBX 3BX processes the signal separately in three bands - LF, MF and HF

Once upon a time, equalizers were a taken-for-granted component of an audio system, and no one was afraid of them. Today it is not required to equalize the blockage of high frequencies of a magnetic tape, but with the ugly dynamics it is necessary to solve something, brothers.

The second part of the series is devoted to the functions of optimizing the dynamic range of images. In it we will tell you why such solutions are needed, consider various options for their implementation, as well as their advantages and disadvantages.

Embrace the immensity

Ideally, the camera should capture the image of the surrounding world as a person perceives it. However, due to the fact that the mechanisms of "vision" of the camera and the human eye are significantly different, there are a number of limitations that prevent this condition from being met.

One of the problems that previously faced film camera users and digital camera owners now face is the inability to adequately capture scenes with a large difference in illumination without the use of special devices and / or special shooting techniques. The peculiarities of the human visual apparatus make it possible to perceive the details of high-contrast scenes equally well in both brightly lit and dark areas. Unfortunately, the camera sensor is not always able to capture the image as we see it.

The greater the difference in brightness in the photographed scene, the higher the likelihood of loss of detail in highlights and / or shadows. As a result, instead of a blue sky with lush clouds, only a whitish spot appears in the image, and objects located in the shadows turn into indistinct dark silhouettes or completely merge with the surrounding environment.

In classical photography, to assess the ability of a camera (or media in the case of film cameras) to transmit a certain range of brightness, the concept is used photographic latitude(see the sidebar for details). Theoretically, the photographic latitude of digital cameras is determined by the digit capacity of the analog-to-digital converter (ADC). For example, when using an 8-bit ADC, taking into account the quantization error, the theoretically achievable value of the photographic latitude will be 7 EV, for a 12-bit ADC - 11 EV, etc. However, in real devices, the dynamic range of images is atthe same theoretical maximum due to the influence of various kinds of noise and other factors.

Large variations in brightness levels represent a severe
problem when taking pictures. In this case, the capabilities of the camera
was not enough to adequately transfer the most
bright areas of the scene, and as a result, instead of a blue area
sky (marked with a stroke) a white "patch"

The maximum brightness value that a photosensitive sensor can record is determined by the saturation level of its cells. The minimum value depends on several factors, including the thermal noise of the array, charge transfer noise, and ADC error.

It is also worth noting that the photographic latitude of the same digital camera may vary depending on the sensitivity value set in the settings. The maximum dynamic range is attainable when the so-called basic sensitivity is set (corresponding to the minimum possible numerical value). As the value of this parameter increases, the dynamic range decreases due to the increasing noise level.

The photographic breadth of modern digital camera models with large sensors and 14- or 16-bit ADCs ranges from 9 to 11 EV, which is significantly greater than that of 35 mm format color negative films (on average from 4 to 5 EV ). Thus, even relatively inexpensive digital cameras have a photographic width sufficient to adequately convey most typical amateur photography subjects.

However, there is a different kind of problem. It is related to the restrictions imposed by existing recording standards digital images... Using the JPEG format with 8 bits per color channel (which has now become the de facto standard for recording digital images in the computer industry and digital technology), it is not even theoretically possible to save a picture with a photographic width of more than 8 EV.

Suppose that the ADC of a camera produces an image with a resolution of 12 or 14 bits, containing distinguishable details in both highlights and shadows. However, if the photographic latitude of this image exceeds 8 EV, then in the process of converting to a standard 8-bit format without any additional actions (that is, simply by discarding "extra" bits), some of the information recorded by the light-sensitive sensor will be lost.

Dynamic range and photographic latitude To put it simply, the dynamic range is defined as the ratio of the maximum value of the image brightness to its minimum value. In classical photography, the term photographic latitude is traditionally used, which essentially means the same thing. The width of the dynamic range can be expressed in terms of a ratio (for example, 1000: 1, 2500: 1, etc.), but most often a logarithmic scale is used for this. In this case, the value of the decimal logarithm of the ratio of the maximum brightness to its minimum value is calculated, and after the number, an uppercase letter D (from the English density? - density) is put, less often? - the abbreviation OD (from the English optical density? - optical density). For example, if the ratio of the maximum brightness value to the minimum value of a device is 1000: 1, then the dynamic range will be 3.0 D: To measure photographic latitude, the so-called exposure units are traditionally used, denoted by the abbreviation EV (from the English exposure values; professionals often call them “stops” or “steps”). It is in these units that the amount of exposure compensation is usually set in the camera settings. Increasing the photographic latitude value by 1 EV is equivalent to doubling the difference between the maximum and minimum brightness levels. Thus, the EV scale is also logarithmic, but in this case, the base 2 logarithm is used to calculate the numerical values. For example, if any device provides the ability to capture images, the ratio of the maximum brightness to the minimum value of which reaches 256: 1, then its the photographic latitude is 8 EV:

Compression is a smart compromise

The most efficient way to preserve the full image information captured by the camera's light sensor is to record images in RAW format. However, such a function is not available in all cameras, and not every amateur photographer is ready to engage in painstaking work on the selection of individual settings for each shot.

To reduce the likelihood of loss of detail in high-contrast images, converted inside the camera to 8-bit JPEG, in the devices of many manufacturers (not only compact, but also SLR), special functions have been introduced that allow you to compress the dynamic range of the saved images without user intervention. By reducing the overall contrast and losing an insignificant part of the information of the original image, such solutions allow you to save in 8-bit JPEG format the details in highlights and shadows captured by the light-sensitive sensor of the device, even if the dynamic range of the original image is wider than 8 EV.

One of the pioneers in the development of this direction was the HP company. Launched in 2003, the HP Photosmart 945 digital camera introduced the world's first HP Adaptive Lightling technology, which automatically compensates for low light levels in dark areas of images and thus retains shadow detail without the risk of overexposure (which is very important when shooting high-contrast scenes). The HP Adaptive Lightling algorithm is based on the principles set forth by the English scientist Edwin Land in the RETINEX theory of human visual perception.

HP Adaptive Lighting menu

How does Adaptive Lighting work? After obtaining a 12-bit image of the image, an auxiliary monochrome image is extracted from it, which is actually a light map. When processing the image, this map is used as a mask that allows you to adjust the degree of influence of a rather complex digital filter on the image. Thus, in the areas corresponding to the darkest points of the map, the impact on the image of the future image is minimal, and vice versa. This approach allows you to show details in the shadows by selectively brightening these areas and, accordingly, reducing the overall contrast of the resulting image.

Note that when Adaptive Lighting is enabled, the captured image is processed as described above before the final image is written to a file. All described operations are performed automatically, and the user can only select one of the two modes of Adaptive Lighting (low or high exposure) in the camera menu, or disable this function.

Generally speaking, many specific functions of modern digital cameras (including the face recognition systems discussed in the previous article) are a kind of by-products or conversion products of research projects that were originally performed for military customers. When it comes to image dynamic range optimization functions, one of the most well-known providers of such solutions is Apical. The algorithms created by its employees, in particular, underlie the work of the SAT (Shadow Adjustment Technology) function, implemented in a number of Olympus digital cameras. Briefly, the SAT function can be described as follows: based on the original image of the image, a mask is created corresponding to the darkest areas, and then the exposure value is automatically corrected for these areas.

Sony has also acquired a license to use Apical's developments. Many Cyber-shot compact cameras and alpha series DSLRs have a so-called Dynamic Range Optimizer (DRO) feature.

Photos taken with the HP Photosmart R927 with (top) disabled
and activated Adaptive Lighting

Correction of the snapshot when DRO is activated is performed during the initial processing of the image (that is, before the recording of the finished JPEG file). In the basic version, the DRO has a two-stage setting (in the menu you can select the standard or advanced mode of its operation). When you select Standard mode, based on an analysis of the image image, the exposure value is corrected, and then a tonal curve is applied to the image to equalize the overall balance. Advanced mode uses a more sophisticated algorithm that allows you to make corrections in both shadows and highlights.

Sony developers are constantly working to improve the DRO algorithm. For example, in the a700 SLR camera, when you activate the advanced DRO mode, you can select one of five correction options. In addition, the ability to save three variants of one image at once (a kind of bracketing) with different DRO settings is implemented.

Many Nikon digital cameras are equipped with D-Lighting, which is also based on Apical algorithms. However, unlike the solutions described above, D-Lighting is implemented as a filter for processing previously saved images using a tonal curve, the shape of which allows you to make shadows lighter, while keeping the rest of the image unchanged. But since in this case, already finished 8-bit images are processed (and not the original image of the frame, which has a higher bit depth and, accordingly, a wider dynamic range), the possibilities of D-Lighting are very limited. The user can get the same result by processing the image in a graphic editor.

When comparing the enlarged fragments, it is clearly visible that the dark areas of the original image (left)
lighter when Adaptive Lighting is enabled

There are also a number of solutions based on other principles. So, in many cameras of the Lumix family from Panasonic (in particular, DMC-FX35, DMC-TZ4, DMC-TZ5, DMC-FS20, DMC-FZ18, etc.), the Intelligent Exposure function is implemented, which is an integral part of the system. Intelligent Auto Shooting Control iA. Intelligent Exposure relies on the automatic analysis of the frame image and correction of dark areas of the image to avoid loss of detail in the shadows, as well as (if necessary) compress the dynamic range of high-contrast scenes.

In some cases, the operation of the dynamic range optimization function involves not only certain operations for processing the original image of the image, but also the correction of shooting settings. For example, in the new models of Fujifilm digital cameras (in particular, in the FinePix S100FS), the function of expanding the dynamic range (Wide Dynamic Range, WDR) is implemented, which, according to the developers, allows increasing the photographic latitude by one or two stops (in the terminology of settings - 200 and 400%).

When the WDR function is activated, the camera takes pictures with exposure compensation of –1 or –2 EV (depending on the setting selected). Thus, the image of the frame is obtained underexposed - this is necessary in order to preserve the maximum information about the details in the highlights. The resulting image is then processed using a tonal curve to even out the overall balance and adjust the black level. The image is then converted to 8-bit format and recorded as a JPEG file.

Dynamic range compression allows for more detail
in highlights and shadows, but the inevitable consequence of such an impact
is the reduction in overall contrast. In the bottom image
the texture of the clouds is much better worked out, however
due to the lower contrast, this image is
looks less natural

A similar function called Dynamic Range Enlargement is implemented in a number of compact and SLR cameras from Pentax (Optio S12, K200D, etc.). According to the manufacturer, the use of Dynamic Range Enlargement allows you to increase the photographic latitude by 1 EV without losing detail in highlights and shadows.

A similar function called Highlight tone priority (HTP) is implemented in a number of Canon DSLR models (EOS 40D, EOS 450D, etc.). According to the information in the user manual, activating HTP can improve the detail in highlights (more specifically, in the range of levels from 0 to 18% gray).

Conclusion

Let's summarize. Built-in dynamic range compression function allows you to convert the original image with a high dynamic range to 8-bit with minimal damage jPEG file... In the absence of a RAW capture function, Dynamic Range Compression allows the photographer to more fully exploit the potential of their camera when shooting high-contrast scenes.

Of course, keep in mind that dynamic range compression is not a magic bullet, but rather a compromise. You have to pay for the preservation of details in highlights and / or shadows by increasing the noise level in the dark areas of the image, reducing its contrast and somewhat coarsening the smooth tonal transitions.

Like any automatic function, the dynamic range compression algorithm is not a fully universal solution to improve absolutely any picture. And therefore, it makes sense to activate it only in those cases when it is really necessary. For example, in order to capture a silhouette with a well-defined background, the dynamic range compression function must be turned off - otherwise, the effective scene will be hopelessly ruined.

Concluding the consideration of this topic, it should be noted that the use of the dynamic range compression functions does not allow "stretching" on the resulting image details that were not captured by the camera sensor. To get a satisfactory result when shooting high-contrast scenes, you need to use additional devices (for example, gradient filters for photographing landscapes) or special techniques (such as taking multiple exposure-bracketing frames and then combining them into one image using Tone Mapping technology).

The next article will focus on the burst function.

To be continued

Compression is one of the most mythical themes in sound production. They say that Beethoven even scared her neighbors' children :(

Okay, actually, applying compression is no more difficult than using distortion, the main thing is to understand how it works and have good control. What we are together now and see.

What is audio compression

The first thing to understand before preparation is compression. work with dynamic range of sound... And, in turn, nothing else but the difference between the loudest and quietest signal levels:

So, compression is the compression of the dynamic range... Yes, just dynamic range compression, or in other words decrease the level of loud parts of the signal and increase the volume of quiet... No more.

You can reasonably wonder why such a hype is connected then? Why is everyone talking about recipes for proper compressor settings, but no one shares them? Why, in spite of the huge number of cool plugins, are expensive vintage compressor models still used in many studios? Why do some producers use compressors at extreme settings, while others do not use them at all? And which of them is right after all?

Compression tasks

The answers to such questions lie in the plane of understanding the role of compression in working with sound. And she allows:

1. Emphasize attack sound, make it more pronounced;
2. "Fit" individual instrument parts into the mixby adding power and "weight" to them;
3. Enhance instrument groups or an entire mix, such a single monolith;
4. Resolve conflicts between instruments using sidechain;
5. Correct the flaws of the vocalist or musiciansaligning their dynamics;
6. With a certain setting act as an artistic effect.

As you can see, this is no less significant creative process than, say, coming up with melodies or introducing interesting timbres. Moreover, any of the above tasks can be solved using 4 main parameters.

The main parameters of the compressor

Despite the huge number of software and hardware models of compressors, all the "magic" of compression occurs when correct setting main parameters: Threshold, Ratio, Attack and Release. Let's consider them in more detail:

Threshold or threshold, dB

This parameter allows you to set the value from which the compressor will operate (that is, compress the audio signal). So, if we set the threshold to -12dB, the compressor will only work in those places of the dynamic range that exceed this value. If all our sound is quieter than -12db, the compressor will simply let it pass through itself, without affecting it in any way.

Ratio or compression ratio

The ratio parameter determines how strongly the signal exceeding the threshold will be compressed. A little math to complete the picture: let's say we set up the compressor with a threshold of -12dB, ratio 2: 1 and fed it a drum loop in which the kick volume is -4dB. What will be the result of the compressor in this case?

In our case, the barrel level exceeds the threshold by 8dB. This difference in accordance with the ratio will be compressed to 4dB (8dB / 2). Together with the unprocessed part of the signal, this will lead to the fact that after processing by the compressor the kick volume will be -8db (threshold -12dB + compressed signal 4dB).

Attack, ms

This is the time after which the compressor will react if the threshold is exceeded. That is, if the attack time is higher than 0ms - compressor starts compressing exceeding the threshold signal not instantly, but after a specified time.

Release or recovery, ms

The opposite of an attack - the value of this parameter allows you to specify how long after the signal level returns below the threshold the compressor will stop compressing.

Before we move on, I strongly recommend taking a well-known sample, hanging any compressor on its channel and experimenting with the above parameters for 5-10 minutes to securely fix the material.

All other parameters are optional... They may differ in different compressor models, which is partly why producers use different models for some specific purpose (for example, one compressor for vocals, another for a drum group, and a third for a master channel). I will not dwell on these parameters in detail, but will only give general information to understand what it is all about:

• Knee or Knee (Hard / Soft Knee)... This parameter determines how fast the ratio will be applied: hard along the curve or smooth. Note that in Soft Knee mode, the compressor does not work in a straight line, but starts smoothly (as far as it may be appropriate when we are talking about milliseconds) to compress the sound already before the threshold value... To process groups of channels and the general mix, it is the soft knee that is most often used (since it works imperceptibly), and to emphasize the attack and other features of individual instruments - hard knee;
• Response Mode: Peak / RMS... Peak mode is justified when you need to tightly limit amplitude bursts, as well as on signals with a complex shape, the dynamics and readability of which must be fully conveyed. RMS mode is very gentle on the sound, allowing you to thicken it while maintaining the attack;
• Lookahead... This is the time it takes for the compressor to know what it will take. A kind of preliminary analysis of incoming signals;
• Makeup or Gain... A parameter that allows you to compensate for the decrease in volume as a result of the compression operation.

First and the most important advice, which removes all further questions on compression: if you a) understood the principle of compression, b) you firmly know how this or that parameter affects the sound, and c) managed to try several different models — you don't need any advice.

I am absolutely serious. If you carefully read this post, experimented with the standard compressor of your DAW and one or two plug-ins, but still did not understand in what cases you need to set large attack values, which ratio to use and in which mode to process the original signal, then you will. continue to search the Internet for ready-made recipes, applying them thoughtlessly anywhere.

Compressor Fine Tuning Recipes it's like recipes for fine-tuning a reverb or chorus - devoid of any sense and has nothing to do with creativity. Therefore, I persistently repeat the only correct recipe: arm yourself with this article, good monitor headphones, a plug-in for visual control of the waveform, and spend the evening with a couple of compressors.

Take action!

Encoding technology used in DVD players with proprietary

sound decoders and receivers. Dynamic range compression (or reduction) is used to limit the peaks in sound when watching movies. If the viewer wants to watch a film in which sudden changes in volume level are possible (a film about a war,

for example), but does not want to disturb his family members, then DRC should be enabled. Subjectively, by ear, after turning on DRC, the proportion of low frequencies in the sound decreases and high sounds lose their transparency, so you should not turn on the DRC mode without need.

DreamWeaver (See - FrontPage)

A visual hypertext document editor developed by the software company Macromedia Inc. The powerful professional DreamWeaver software contains the ability to generate hTML pages of any complexity and scale, and also has built-in support for large network projects. It is a visual design tool that supports advanced WYSIWYG concepts.

Driver (See p. Driver)

A software component that allows you to interact with devices

computer, such as a network interface card (NIC), keyboard, printer, or monitor. Network equipment (such as a hub) connected to the PC requires drivers in order for the PC to communicate with the equipment.

DRM (Digital Rights Management - Control of access and copying of information protected by copyright, Digital Rights Management)

u A concept that involves the use of special technologies and methods of protecting digital materials to ensure that they are provided only to authorized users.

v Client program to interact with the Digital Rights Management Services package, which is designed to control access to and copying of copyrighted information. DRM Services works in windows environment Server 2003. The client software will run on Windows 98, Me, 2000 and XP, providing applications such as Office 2003 with access to related services. In the future, Microsoft should release a digital rights management module for internet browser Explorer. In the future, it is planned to have such a program on the computer to work with any content that uses DRM technology in order to protect against illegal copying.

Droid (Robot) Agent)

DSA(Digital Signature Algorithm - Digital signature algorithm)

Public key digital signature algorithm. Developed by NIST (USA) in 1991.

DSL (Digital Subscrabe Line - Digital Subscriber Line)

Modern technology supported by city telephone exchanges to exchange signals at higher frequencies than those used in conventional analog modems. DSL modem can work simultaneously with a telephone ( analog signal) and with a digital line. Since the spectra of the voice signal from the telephone and the digital DSL signal do not "overlap"; do not interfere with each other, DSL allows you to surf the Internet and talk on the phone on the same physical line. Moreover, DSL technology usually uses multiple frequencies, and DSL modems on both sides of the line try to find the best ones for data transmission. The DSL modem not only transmits data, but also acts as a router. Equipped with an Ethernet port, the DSL modem makes it possible to connect multiple computers to it.

DSOM(Distributed System Object Model, Distributed SOM - Model of distributed system objects)

IBM technology with appropriate software support.

DSR? (Data set ready - Signal ready to transmit data, signal DSR)

Serial interface signal indicating that a device (e.g.

modem) is ready to send a data bit to the PC.

DSR? (Device Status Report)

DSR? (Device Status Register)

DSS? (Decision Support System)