Practical photography Bunimovich David Zakharovich

What is contrast

What is contrast

In everyday life, we call any sharply expressed opposite contrast. The concept of contrast can be applied to anything. Let's see what this means in photography. Briefly, it can be expressed as follows: contrast is the ability of photographic materials to convey the brightness of the photographed object with varying degrees of difference.

At one time, photographic films of different contrasts were produced. Some films conveyed differences in brightness in the same way as we distinguish them in real life, that is, without distortion. Such films were called normal. Others conveyed these differences with some understatement. They were called soft. Still others, on the contrary, exaggerated the difference in brightness. They were called contrasting.

The task of photography is to correctly, without any tonal distortions, convey the photographed object in the picture, and it is quite obvious that this can be done using only normal films. Therefore, simultaneously with the release of photographic films of the “Photo” type in four degrees of sensitivity, the production of soft and contrasting photographic films was also stopped, and all films of the “Photo” type are now produced only in normal grades.

However, shooting objects are different, and their correct reproduction in a photograph does not always meet the photographer’s creative intent. In practice, we sometimes have to photograph objects that are themselves very sluggish. This is what many objects look like in cloudy weather. It’s a different matter if you intend to consciously emphasize this lethargy, dullness, cloudy weather. Then, of course, it is best to shoot on normal films. But if such a task is not necessary and it happens that the picture needs to be made with contrast, and the weather is cloudy, then a contrast film could help out.

The opposite cases also occur, especially in summer, in clear, sunny weather. Bright sunlight greatly increases the contrast of the subject. When shooting on normal films, the object will turn out to have the same contrast. The details of an object in the shadows may disappear in the photo. In such cases, soft film could soften the contrast and thereby improve the technical quality of the photo.

But the contrast also depends on the development time. Depending on how long you take to develop the film, the negatives may come out with different contrasts. Therefore, contrast can be controlled on normal films as well.

Which TV screen contrast is better, dynamic or static?

Buying an LCD TV in a store is not an easy task. You have to take into account a lot of different parameters, and the cost of the TV is not the first of them. In addition to the diagonal, type and country of manufacturer, it is recommended to pay attention to the specified contrast values ​​of the picture displayed on the LCD TV screen. And if image quality is extremely important to you, then pay attention to how contrasting a picture a particular model can produce.

What is contrast?

What is LCD TV contrast? We are talking about the ratio of the brightness of two points, one of which corresponds to the lightest, and the other to the darkest area. Simply put, by indicating the contrast of the TV image, the manufacturer shows how many times the lightest point of the screen is brighter than the darkest point of the screen that the LCD TV screen is capable of producing. Of course, it is impossible to determine the exact contrast parameters by eye. To determine the contrast, the TV must undergo a special test using high-precision instruments. This means that manufacturers who indicate certain contrast indicators have to take their word for it. Alternatively, you can read one of the reviews or testimonials on various sites and forums. Here we post unbiased information from users who tested this model LCD TV in person.

Types of Contrast

As we have already said, contrast can be not only static, but also dynamic. Static contrast, also called natural, will determine the capabilities specific model LCD TVs. Well, dynamic contrast can be achieved through the use of special technologies. Static contrast is taken from the brightness of an individual pixel viewed in a static (motionless) scene. That is, a still image is taken, in which the darkest and brightest points are selected, after which the accepted formula is used. Dynamic contrast is measured only after contrast enhancement technology is applied to the picture. LCD TVs have the ability to regulate contrast, focusing on the plot of the video being played back.

Benefits of Static Contrast

Of course, LCD TVs with high static contrast rates are valued much higher than those with high dynamic contrast rates. And this is completely justified. It is enough to display a picture with white text on a black screen. A TV with high natural contrast will actually show white text and black background.

As for a TV with dynamic contrast, white letters on a black background will appear gray. From this we conclude that TVs with high natural contrast will show more realistic regular video, which is highly valued by amateurs high-quality image. For example, in daylight a black car on the screen will be really black, but in the evening it will be possible to distinguish bright colors without any problems. Street lights. Approximately the same image, in terms of contrast, can be seen in modern cinemas.

TVs with perfect contrast

It is worth noting that in terms of contrast the maximum realistic image They gave CRT models of TVs. But today, when HDTV is in fashion, CRT TVs are no longer produced. As a result, the “yellow jersey of the leader” has been handed over to LCOS home projectors with the highest natural contrast, among which JVC D-ILA devices stand out. Following them we can distinguish Sony devices SXRD. And only after them good contrast demonstrate modern plasma TVs.

Local dimming

IN last years Manufacturers of LCD TVs managed to introduce certain technologies that made it possible to achieve an acceptable level of contrast. Particularly impressive results were achieved through the use of LED backlight with local dimming technology. Of course, you won’t be able to adjust every pixel; control is carried out only by a group of LEDs, but the result is more than worthy. Ideally, the backlight LEDs should be located across the entire screen. But manufacturers deliberately abandoned such models, since they were too high cost, inaccessible wide group consumers. Modern LCD TVs use edge lighting, in which LEDs are located at the top and bottom. The edge lighting can also work with local dimming technology. Edge-lit LCD TVs display impressive contrast when using local dimming.

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(CRT) completely disappeared from store shelves computer equipment, giving way to their liquid crystal counterparts. People unfamiliar with this technology often get confused about the terms, since there are several names for the same item. To avoid misunderstandings, let's immediately clarify this issue: LCD, LCD - all these are the same liquid crystal technology, and not different. LCD stands for Liquid Crystal Display. Indirectly, the term “TFT” can be attributed here, meaning the use of thin-film transistors to control the matrix. Since they are not used in CRTs, it is obvious that the mention of TFT indicates LCD.

Having replaced old CRT monitors with modern LCDs, many owners were faced with an amazing phenomenon - in the first time after the transition, their eyes began to hurt, and for some, even Hence the subsequent question - “how is it done for the eyes.” There are many recommendations on the Internet, but most of them are incomplete, because the very reason for what is happening is cleverly overlooked. Indeed, if monitor contrast and brightness in LCD and CRT technologies are similar concepts, then where does the discomfort in the eyes come from when working with LCD? After all, this shouldn’t happen. The real reason for eye fatigue is that the operating principle of the backlight is based on gas discharges in the tube, and even modern LED backlights also have flickering (read about PWM control of LEDs). In addition, the color of the glow, both the lamp and the diodes, is unnatural; it has a defective spectrum. It’s invisible to the eye, but you can’t fool the visual receptors.

In general, monitor contrast is numeric value, which is the ratio of the brightness differences between the lightest white point and the darkest black point. In monitors it is indicated in the form “xxx:y”. In fact, it's a different way of writing. For example, the contrast of a monitor with a maximum point brightness of 300 cd/m2 and a minimum of 0.5 cd/m2 will be (300-0.5)/0.5 = 599:1. It is generally accepted that the higher the contrast value, the clearer the picture. This is partly true, but only to a certain limit, since an infinite increase leads to image distortion (light details on a white background cease to be distinguishable). If the monitor contrast is not adjusted properly, then this is one of the reasons for the feeling of sand in the eyes when changing from CRT to LCD.

Note that all methods of setting parameters offered on the Internet are subjective. Each user must make adjustments based solely on personal preferences. In the operating room Windows system 7 there is a built-in monitor brightness setting that allows you to optimally set the brightness values, as well as contrast and gamma.

On the desktop click right button mouse, go to “Screen Resolution”, then “Make text and other elements larger or smaller” and “Color calibration”. By clicking “Next”, we follow the wizard’s advice (there is also detailed help here). At the end, you will be asked to configure the display of fonts using Clear Type technology: in the samples we indicate the clearest and “boldest” lines of letters.

Additionally, you can configure the monitor itself. To do this, set the contrast to 20-40%, and achieve a high-quality image with brightness. In some cases, the brightness may be zero, which is quite acceptable. The color temperature (deviation into the yellow or blue spectrum) must be set based on the yellow tint corresponding to color temperature sunlight (6300 K). Various image enhancement mechanisms and dynamic contrast do not allow you to correctly configure the monitor, so you need to compare the enhanced and natural operating modes and choose the best one for yourself.

They are no longer a new product, but they are an important attribute of every computer. Let's try to briefly talk about the main features of modern LCD monitors in order to have general idea about what we are going to buy.

First, let's highlight the main characteristics that you should pay attention to when choosing a monitor. These characteristics are: diagonal, matrix resolution, matrix technology, matrix backlight technology, viewing angles and options for connecting the monitor to a computer and other devices.

Diagonal and resolution

Undoubtedly, screen size is a purely individual characteristic and everyone selects it depending on the tasks they set for the monitor. But the combination of diagonal and monitor resolution is worth stopping at.

Let us recall that the resolution of a matrix (monitor) is the ratio of the number of pixels in height and width. Modern monitors generally have a resolution of 1366x768 (HD Ready) and 1920x1080 (Full HD), but since the resolution also depends on the geometry of the monitor, it can also be 1600x900 or 1680x1050.

It is very important that a monitor of the same diagonal can have a resolution of 1366x768 and 1920x1080. The difference here is obvious - the number of pixels is strictly tied to physical size matrices, which in turn means that the size of the pixel itself in monitors with a resolution of 1920x1080 is smaller than in monitors with a resolution of 1366x768. This means that more graphic information can fit on a monitor with a resolution of 1920x1080.

It's worth thinking about this if you plan to use the monitor to watch videos or television programs. We explain why: the diagonal is the same, the viewing distance is the same, the video file is the same (for example movie dvd) - different resolution and the image quality is also different. In “full screen” mode, the quality is higher on a monitor with a resolution of 1366x768, because the video file has the same resolution. If you imagine that a video file has a resolution of 800x600 pixels, then you can understand that the higher the monitor resolution, the more picture"stretched" and therefore the image quality decreases. For comfortable viewing, you will have to acquire HD quality files.

Of course monitors with Full resolution HD is a step forward, but if you are not ready for such changes or do not intend to watch video, HD Ready monitors are perfect, especially if you plan to use the monitor as a TV and watch over-the-air television.

Viewing angles, brightness and contrast of LCD monitors

In fact, there’s no point in stopping and thinking about these parameters. In modern monitors, there cannot be a viewing angle less than 170°, and hardly anyone is able to look at such an angle. This characteristic is a relic of the past.

The image contrast is very important parameter, although there are no significant differences here either. There is a concept of static contrast and dynamic (DC). Of course, static contrast is more important, but you should understand what dynamic contrast means.

We are talking about the type of image that changes - video, games. In any frame there are both light and dark moments and the human eye perceives them as a whole, that is, if most of the screen is light, then the black level in a few dark areas of great importance does not have, and vice versa. That's why, automatic adjustment The brightness of the backlight depending on the image is a completely reasonable thing. It is this automatic adjustment that is dynamic contrast.

The numbers for dynamic contrast are obtained very simply: if the static contrast is 1000:1, and the monitor electronics allow you to change it by 3 times, then the dynamic contrast is within 3000:1. Dynamic contrast numbers always look larger and sometimes shocking, but it’s still worth looking towards the static value. The higher the better.

Not a single modern monitor has static contrast below 1000:1. If you are into video games, then you need not only high static but also dynamic contrast.

Brightness is a little easier. In the parameters of modern LCD monitors it is in the range of 200 - 350 cd/m². At night these numbers mean absolutely nothing, but during the day they matter a little. To work in bright areas or in a building with a sunny side, of course, it would be better to have more brightness.

Matrix technology

Let's briefly look at the main monitor matrix technologies, which are TN (TN+film), IPS and *VA. The last one has an asterisk because there are two similar, with minor differences, technologies - MVA and PVA. So, TN+film technology is the most common. The advantages are a short response time, which is very important in dynamic images of videos and video games (shooting games, racing games) and a low price. We can say that monitors based on TN matrices are universal monitors.

Monitors on IPS based matrix is ​​much more expensive than TN monitors. The main disadvantages, if you do not take into account the price, are more high time response and, as a common drawback of almost all LCD matrices, insufficient black blackness. But, compared to TN monitors, IPS provide more believable TrueColor and more realistic viewing angles. The picture looks noticeably better and more contrasty. Such monitors are more suitable for those who work with graphics, since their soft and accurate color reproduction is almost as good as that of CRT monitors. All professional monitors for working with graphics are made on an IPS matrix.

Monitors based on *VA matrices. Both viewing angles and color rendering *VA monitors are much better than TN, however IPS matrices these parameters are inferior. Response time is longer than TN monitors. Perhaps the main advantage of *VA monitors is the unprecedented contrast for LCD matrices, which gives almost real black color. Such monitors are better suited for those who work with text, black on white and vice versa, drawing graphics.

Matrix backlight technology

Today the most advanced is LED backlight, based on the principle of LED lighting. The service life of LED backlighting is 40% greater than that of conventional CCFL backlighting, which is slowly beginning to take its place in history.

We won't dwell too much on the details. The Imagine store recommends monitors with LED backlighting.

Connecting the monitor to a computer and other devices

Today, the main monitor connection interfaces are D-Sub (VGA), DVI and HDMI.

D-sub - analog interface. The presence of such a connector in a modern monitor can only be justified by connecting more old computer or other equipment. The video signal is transmitted in analog form, which does not exclude interference and other bad influences.

DVI - digital interface. This type connection provides for transmission digital signal, thanks to which it is achieved best quality images and color rendering. If your computer's video card has such a connector, it is better to choose a monitor with a DVI interface.

And finally, the HDMI interface. His fundamental difference from DVI is that in addition to digital video, multi-channel is also transmitted digital audio. HDMI Interfaces and DVI use different type connectors but an identical coding system, so they can easily be connected to each other using a simple adapter

That's all that can be highlighted in modern LCD monitors. We hope our advice will help you choose what you need.

When talking about the contrast of a projector, first of all you should separate the contrast of the device itself and image contrast.

For example, to test a projector, I need to measure the contrast of the device itself, but when building a home theater, I need to know the contrast of the image, which consists not only of the contrast of the projector. In general, there are several ways to measure contrast, and the differences between them are not always obvious or intuitive.

What is contrast?

Another long introduction...

When talking about an image, contrast is the ratio of the brightness of white to the brightness of black.

To be pedantic, the “brightness” of the image (measured in foot-lamberts or nits) is measured from the screen, and there is also the luminous flux (lumens) or illuminance (lux), which is measured measuring device aimed at the projector.

All of these parameters can be used to determine contrast, but each has its own specifics, which will be discussed later.

The main thing for now is to understand the principle that we divide the “brightest” by the “darkest” - and get contrast. High contrast means high maximum brightness with "deep black levels". Low contrast is when the black color looks like gray, but the white color is not bright enough.

The peculiarities of our vision are such that there is a certain full range of brightness perceived by the eye with adaptation, and there is a range of brightness perceived without adaptation. For example, there is a story that pirates allegedly used an eye patch so that, upon breaking into the hold, they would have one eye already prepared for dark conditions. In other words, the eye is definitely not able to simultaneously cover the range of brightness that would include the darkness of the hold and the bright Caribbean sun on the deck - adaptation is required.

To create a contrasting scene at the projector, we, thank God, do not have to blind the viewer, although this is assumed by the HDR/UltraHD standards. For the familiar SDR, it is quite enough to repeat the brightness range that would be perceived by the eye as “contrast” without adaptation. It’s worth remembering here that SDR assumes that 100% white is the color against which you are this moment you read this text, and not the blinding light of some spotlight or desert sun in the viewer’s face.

I briefly inquired about the sensitivity of the eye. There is an opinion that without adaptation the eye perceives, in the language of photographers, “from 10 to 14 stops,” which in theory should correspond to a contrast (the ratio of bright to dark) from 1024:1 to 16384:1 (though I don’t know in which ones exactly) conditions).

1024:1 is usually not a problem for DLP projector for home entry level, well, 16,000 or more is definitely the top segment, although it is far from the limit of the projectors’ capabilities. In general, there is nothing outrageous about creating a contrasting picture.

But right away important note. If I, as it were, propose to “prohibit the eye from using adaptation,” then let the projector’s specified contrast levels also be “fair” or “native.” The opposite of "native" is "dynamic" contrast, which is achieved using techniques such as automatic iris. In other words, we cannot see dynamic contrast in one image, but only sequentially - first on a dark, then on a white scene. And we should be able to see the “native” contrast on one stage.

Black depth

If we talk about contrast effects, then for starters we can separately mention the effect of brightness and black depth. It's clear that brightness is needed to make you believe you're on a sunny beach, or that the water is actually throwing reflections in your face. Especially high brightness is important in order to draw sunny weather...

The problem is that if there is a bright object, the eye will adjust to it and will be less picky about black. On a bright scene, even a “bad black” will look black, not only due to the adaptation of the eye, but also psychologically:

It turns out that we take two projectors with a contrast ratio of, for example, 2000:1. One will have deep blacks, the other will not, but will have extra brightness. That is, the level of black color should be discussed separately from contrast.

This suggests that the owner of an overly bright projector has two simple options: enjoy the high brightness, sacrificing blacks, or reduce brightness, improving blacks. For classic HD content there is a recommended brightness for the image, which in most cases is achieved at luminous flux 1000 lumens or less (in the appropriate picture mode). If, let’s say, the projector produces 2000 lumens in the exact mode, and your screen size is 90 inches (that is, small), then you should probably worry about reducing the brightness. For budget projectors, one of the options is lamp mode (normal/eco), while for top models for this purpose is provided manual setting aperture, or precise adjustment of the brightness of the light source - for “laser manufacturers”. If you are the owner of a budget projector and want to reduce the brightness, then you can look towards gray screens, or even try attaching an ND (neutral neutral) filter to the lens. However, I can’t give any exact recommendations.

ANSI contrast

Let's move on to measurements.

ANSI contrast measured from the projector screen, that is, we are talking specifically about his brightness. To measure contrast using the ANSI method, a test image is displayed on the screen in the form chessboard(black and white squares). On this parameter A number of factors other than the projector's capabilities have a huge impact:

• properties of the screen fabric;
• distance from the walls and room size;
• lack of background lighting;
• quality of darkening walls and ceilings, etc.

In this regard, it is important to understand that ANSI contrast is used to evaluate not the projector, but home theater, that is, a projector + screen + room system.

The first thing that catches your eye when trying to display a black and white checkerboard in an unprepared room is that the light from the white checkers, reflected from the ceiling, returns to the black checkers, significantly degrading the black level and contrast level. In most films, it is the simultaneous depth of black and brightness of white that gives the picture realism and the immersive effect, creates quality content the impression of volume, three-dimensionality. Therefore, ANSI contrast is exactly what you need to evaluate a home theater.

However, compare projectors Using ANSI contrast is difficult. If the author of the comparison is ready to guarantee that all measurement conditions will remain unchanged throughout the years during which he will make reviews, then (probably) you can take his word for it. However, one reviewer's ANSI contrast will be difficult to compare with another reviewer's ANSI contrast.

Why is this parameter so popular when testing projectors? The answer is that it completely eliminates the dynamic contrast factor. By measuring contrast using a checkerboard pattern, we don't give the projector any chance to engage the auto iris, which can increase contrast by 100 times or more, darkening blacks. Projectors with a laser light source, for example, allow the light to be turned off completely at any time, producing perfect blacks. But this will be useless when testing for ANSI contrast.

Full On/Off contrast (full on/off)

If ANSI is “simultaneous” contrast, then Full On/Off is “sequential”, that is, black and white measured one by one. This eliminates the influence of white on black and in almost any dark room we can quite accurately measure the brightness of black and determine the contrast the projector itself, if the measuring instrument is pointed at the projector (although significant difference Compared to the measurement, there should be no light reflected from the screen either).

Fundamental importance when using this method is whether the projector has auto iris or similar dynamic contrast enhancement methods (lamp, laser) enabled. If they are turned on, the black color may be 100 times darker or more, and we will measure dynamic contrast. If all this is turned off, then we get native(“fair”) contrast. In any case, we must be 100% sure whether "black enhancement" is used.

What contrast is indicated by the manufacturer?

Most likely dynamic. If it’s native, the numbers will seem too low. For example, when an expensive projector has a contrast ratio of 2000:1, then this is most likely the native contrast.

Dynamic aperture is useful if implemented well. It is also useful to the manufacturer because it allows any contrast to be specified in the specifications. As for, in fact, the correct operation of the diaphragm, there is a lot of uncertainty. For example, at what brightness does it start to work? Or will it turn on if there is a very small bright area on the screen? There are a lot of nuances, and the apertures of expensive projectors usually work more quietly and accurately.

The native contrast of the projector is highly dependent on the color rendering mode. The highest contrast ratio is usually achieved in the brightest mode, as color correction and calibration is inevitable reduce maximum brightness, but the black brightness remains the same.

Here's an example: in the bright mode, the white is slightly green, and to create an accurate mode for watching movies, we reduce the brightness of the green, which ultimately gives us the correct shade of white (neutral, colorless). As a result, the brightness of white decreased due to the loss of excess green, and the brightness of black remained the same (as much excess light as the projector matrix let through, so much does it let through). As a result, the mode seems to be intended for cinema, and the contrast turned out to be lower than in the bright mode, intended for a lit room.

Illuminated room

Rooms without prepared surfaces have a significant impact on the black level, but any external light simply kills it. In this regard, if there is possible flare in the room, the black produced by the projector itself (black depth) becomes less significant as brighter light, and maximum brightness is more significant. As a result, for office and school projectors, if they are operated in the light, everything turns upside down. The contrast of the projector is no longer important (since it is measured in the dark), but the brightness is important, which will increase the level of real ANSI contrast.

Sometimes contrast in such conditions refers to legibility (for example, text). The minimum contrast level that produces relative legibility is approximately 4:1, although an image with a contrast ratio of 7:1 or 10:1 can be considered adequate. For office projectors, the quality of color rendering in the brightest modes is of particular importance, since poor color rendering on maximum brightness may force the user to switch to a less bright mode, losing contrast/legibility.

It is worth noting that, despite the fact that black can be considered lost in illuminated rooms, this does not prevent you from creating a beautiful and colorful bright image with an emphasis on illuminated objects.

Screen influence

There are several ways the screen can affect black levels. Speaking of the most budget decisions, we are unlikely to go far from choosing between ordinary matte and gray screen. The latter equally absorbs “white” and “black”, and therefore is only suitable for removing excess brightness. As a result, black becomes darker, and white... also darker. If the projector does not have very high contrast, then this may be suitable option if you want to use it in a dark room.

The next level is reflective screens. Unlike usual matte screens, scattering light evenly in all directions, these screens also have a slight “mirror effect”, or “glossy effect” in the sense that they reflect the light incident on the surface more directionally, according to the principle “the angle of incidence is equal to the angle of reflection”. Therefore, the viewing angle of these screens is lower, as is the uniformity of brightness. But they tend to reflect unwanted light falling from the side not at the viewer, but “somewhere else,” as a result of which the black level improves (especially in rooms that are not ideal from the point of view of a home theater). As a trade-off for this, spectators must be positioned in a narrower area.

At the forefront of technology are multi-layer ALR (Ambient Light Rejection) screens. They “eat up” side light more effectively, although they are significantly more expensive - this is clearly not a solution for a budget home theater. Typically, it's also about reflecting or absorbing light coming from the side and enhancing light coming from the side of the projector.

demonstration of the effect of ALR screen fabric CineGrey 5D

Gamma correction

Gamma correction is what happens to the brightness of the projector between black and white. In other words, the projector's response curve to the signal. For example, what percentage of maximum brightness will the projector output if it is commanded to “show 10% brightness”? Answer: not 10%.

In a lit room, a sharper increase in brightness is required for dark shades (shadows) so that they are distinguishable and do not merge. If you use a projector set for a lit room in a dark environment, the detail of dark objects will be overly emphasized and the image will be look low-contrast. In order for the picture to look contrasty and natural, gamma correction must be set correctly. You can read more about gamma.

Conclusion

I just wanted to say that the topic is extensive and this article will be updated. But that's all for now. Thank you for your attention!