Technologies of obtaining of color images were included into an everyday life rather recently. Still there were in family albums black-and-white photos, and on summer residences live the long century black-and-white TV sets.

However, and now black-and-white images are widely used there where color is not mandatory, or as art effect.

Obviously, for image transfer there are enough shades of one color. If it is a question of emitted colors the same color is meant color hue, but different on brightness. In the black-and-white TV set the image is formed by points of phosphor which can be shone with various brightness. Differently, the image is under construction of shades of gray of color from black (minimum brightness) to white (the maximum brightness). If phosphor was shone, for example, by brown color the image would be constructed of shades of the brown.

Colors on a print do not radiate light, therefore their shades differ in optical density. Optical density serves as a measure of absorption of light. The above optical density, the a shade is more dark. If the image is printed not in shades of gray, and any other color, say that it тонировано. Recall, for example, old photos in tones сепии.

In computer graphics such images are called as half-tone as consist of shades of one color tone. In graphic programs including in Photoshop, each color can have 256 shades:

From black (zero brightness) to white (brightness is equal 255). The information on brightness пикселов images is stored in the channel. Thus, for the halftone image enough one channel.

1. Open the image Girl.jpg with applied diskettes.

2. Open a palette of channels (fig. 2.3) command Show Channels (to Show channels) menu Window (Window).

Colors are formed in the nature in the various image. On the one hand, light sources (the sun, bulbs, screens of computers and TV sets) radiate light of various lengths of the waves, perceived by an eye as color light. Getting on a surface of not shone subjects, light is partially absorbed, and partially reflected. The reflected radiation is perceived by an eye as a painting of subjects. Thus, color of object results from radiation or reflection. The description of color of object in the first case differs from the second, i.e. different models of color are applied.

Model RGB describes emitted colors and is based on three basic colors — Red (Red), Green (Green), Blue (Dark blue). Remaining colors are formed at mixing of these three cores. At addition (mixing) of two rays of primary colors the result is more light components. Colors of this type are called as additive (fig. 2.4).

From mixing red and green it turns out yellow, green and dark blue — blue, dark blue and red give the magenta. If all three colors mix up, the white is as a result formed. Mixing three basic colors in different proportions (with different brightness), it is possible to receive all diversity of shades. If to speak about the bitmap image in model RGB everyone it пиксел is represented brightness of three basic colors: red, green and dark blue.

As already it was told above, brightness пикселов is stored in channels. Thus, for the RGB-image it is required three channels (fig. 2.5).

The color channel is the halftone image reflecting allocation of brightness of appropriate basic color. If the document has model Grayscale contents of the unique channel and form the image. Editing of the channel and image editing in these cases same.

If document model — RGB images in the red, green and dark blue channel, being superimposed against each other, form a color picture. Thus, note, colors mix up is additive, as rays of light. It means that at superimposing the result is clarified. The the channel is more light, the more than basic color contains in the image. We check up this foggy expression in practice. For learning of interactions of channels it is convenient to display them in color. All operations with channels are led in palette Channels (Channels).

1. Open the document Pyramid.jpg, allocated on a diskette. Pay attention to window title. For полноцветных images in it the color model is underlined.

2. Install flag Color Channels in Color (Color channels in color) in group Display and Cursors (Display and cursors) windows of setting of program Preferences (Setting). If this flag is installed, channels are shown in appropriate color. At the removed flag contents of channels are displayed in shades of gray.

3. Open palette Channels (Channels). Command Show Channels (to Show channels) menu Window (Window) is for this purpose used. Here color channels of the image, everyone by the color (fig. 2.6) are presented. Contrary to waitings, the palette shows four channels as images in color models RGB, CMYK or Lab have the additional combined channel occupying top line of a palette on a palette of channels. It shows the resultant image. The line of the combined channel allows to pass from review of separate channels to review of the total image.

The channels selected for review or editing, are called as active, and all actions executable in a document window, are spread only to them. In palette Channels (Channels) they are selected by illumination. The combined channel is by default active.

1. Click the mouse on channel Red name. Its line will be highlit dark blue, and lines of all remaining channels become white. The image in a document window turns out black-red since as active the red channel is selected.

2. Now select a line of the combined channel. The image again acquired normal color.

3. It is possible to include display of any two channels simultaneously. Click on an icon of "Eyes" at channel Green. Now other two channels — Red and Blue are visible. The icon of "Eyes" defines a channel display mode by sign "visible/invisible". For the combined channel this icon turnes on only when all color channels are visible. One channel, or any pair of RGB-channels always appears more darkly, than result of combination of all of three. It and is not surprising if to remember that colors in this model mix up is additive.

4. Pay attention on specified in line of each channel keyboard equivalents. They allow to select the active channel quickly. Check up these key patterns in operation.

5. To make some channels active, follows at selection by the mouse of the subsequent channels to hold pushed SHIFT key. Try to activate simultaneously any two channels. Unfortunately, the SHIFT key does not operate at a choice of channels by means of the keypad.

Channel contents judge on the reduced picture, a miniature allocated at line of the channel. The miniature in the course of layer editing is permanently updated. If miniatures on the panel of channels seemed to you too small, they can be increased.

1. Click in palette Channels (Channels) on a triangular arrow to the right of tabs. From the opened list of commands select Palette Options (palette Adjustments).

2. On the screen there will be dialog box Channels Palette Options (Adjustment of a palette of channels) (fig. 2.7), in which the unique field defining the size of miniatures. Select to the taste the necessary switch.

3. Push the button APPRX.

In the lower part of a palette three icons which serve for saving of the selected area in the new channel, for creation of the new channel and for channel removal (from left to right) are allocated. These operations are applicable only to additional alpha channels which are considered in the following chapter.

If to present model RGB in a graphic type the three-dimensional system of coordinates turns out. Any coordinate reflects the contribution of each component to resultant color to a range from zero to the maximum value. In the received cube also there are"all colors, forming color space.

It is important to mark especial points and lines of this model.

The beginning of coordinates where all components are equal to zero. Radiation misses (black color). A point nearest to the spectator where all components have the maximum value (white color). A line, connecting first two point (on a diagonal) where gray shades are allocated: from black to white (a gray scale, it is normal — 256 gradation). Here all three components are identical and are in a range from zero to the maximum value. Three peaks of a cube give pure initial colors, remaining three reflect double mixing of initial colors.

HSB — very simple model in understanding in which computer artists often work. It is based on colors of model RGB, but has other system of coordinates. Any color in model HSB is defined by the color tone (actually color), a saturation (i.e. percent of the white color added to color) and brightness (percent of the added black color). The given model received a title on the first letters of English words Hue, Saturation, Brightness, — HSB. Thus, the model has three color channels.

Spectral colors (solid colors of a solar spectrum) or color tone (hue) are allocated on edge of a color circle and characterized by position on it which is defined by value of a corner in a range from About to 360 degrees. These colors possess the maximum saturation and brightness (100 %). A saturation changes on radius of a circle from 0 (at center) to 100 % (on edges). At value of a saturation of 0 % any color becomes white.

Brightness (Brightness) — the parameter defining illuminance or затемненность. All colors of a color circle have the maximum brightness (100 %) without dependence from tone. Reduction of brightness of color means its shading. To display it on model, the new coordinate is required to you. Direct it, for example, downwards, on it you will postpone values of brightness from 100 % to 0 %. The cylinder (or a cone if to cut black colors) which is formed of a series of circles with decreasing brightness, a low layer — black As a result turns out.

In model HSB any color turns out from spectral adding of certain percent of white and black colors, i.e. actually gray color.

Model HSB is not strict from the point of view of human perception. The brightness description in it does not correspond to perception by a human eye. The matter is that the eye sees spectral colors as having various brightness. So, spectral green it is represented to the brightest, red — less bright, and dark blue — the most dark. In model HSB all spectral colors are considered as possessing 100 %-s' brightness that does not represent the facts. We add that it hardware-dependent as actually in its basis model RGB lies. Therefore, if you are going to work with the exact color values, the given color model should be avoided. In Photoshop it is impossible to work immediately with images in this model. At the same time with its help conveniently visually to select colors, and Photoshop gives such possibility.

So brightness in color model HSB is calculated. As, as we already clarified, different basic colors have different perceived brightness, this calculation does not reflect a real state of affairs, therefore, in particular, it is impossible to consider model HSB correct. For calculation of brightness of channels RGB in Photoshopиспользуется the following empirical formula considering the contribution of each color channel:

The color circle can be useful at selection of the necessary color gamma if to consider some remarks on layout of colors on this circle and their mutual combination.

• Complementary colors.
Are opposite each other. At their mixing it is formed black (if it is colors) or white (if it is luminous rays) color. It as much as possible contrast colors, and together they operate approximately раздражающе (red and green, yellow and violet, dark blue and orange). Are applied to creation of the strong color contrast.
• Colors, adjacent with the additional.
One color is combined with two others which are adjacent in relation to its complementary color (green, dark orange, claret). Such combination softer, but contrast enough.
• Triads.
Colors, equidistant from each other on a color circle. Form harmonic combinations (yellow, magenta, blue or orange, emerald, claret) that creates a palette of saturated colors and shades.
• The adjacent colors.
Form a low-contrast combination which gives to a picture a strict type, for example, in circuits or forms of the solid company.

Except color tone, perception of objects of an illustration is influenced always by a saturation and brightness of color. Generally, than more purely tone, i.e. the more both these characteristics, the more strongly object draws attention. If in your picture there is especially important detail, and remaining figures — only a background for it it is reasonable to lower their brightness or a saturation. Saturation lowering leads to picture clarification, it acquires a pastel palette. Lowering of brightness of color, on the contrary, blacks out an illustration. A limiting case of color accent at the expense of a difference of brightness and saturations — a combination of black or white color with spectral that produces the strong effect.

The colored not shone objects absorb a part of a spectrum of this world falling on them, and reflect the remained radiation. Depending on in what area of a spectrum there is an absorption, objects reflect the different colors defining a painting of these objects. Colors which use this world, subtracting from it certain sections of a spectrum, are called as subtractive ("subtractive").

For their description model CMY (Cyan, Magenta, Yellow) is used. In this model primary colors are formed by subtraction of white color of the main additive colors of model RGB. It is clear that in that case and the main subtractive colors too will be three as they were already mentioned: blue (a white minus red), magenta (a white minus green), yellow (a white minus dark blue).

At mixing of two subtractive making resultant color it is blacked out (it is absorbed more light, it is necessary more colors).

Thus, at mixing of the maximum values of all three components black color should turn out. At total absence of color (null values of components) white color (a white paper) is formed. Mixing of equal values of three components gives shades of gray. Model CMY (fig. 2.8) is similar to model RGB in which the beginning of coordinates is moved.

The given model — the main model for polygraphy. Magenta, blue, yellow colors make a so-called polygraphic triad, and at printing by these colors the most part of a visible color spectrum can be reproduced on a paper.

However real colors have impurity, their color does not correspond in accuracy theoretically calculated blue, magenta and yellow. The blue colorant of typographical color, and mixing of three main colors which should give black color "is especially bad", gives instead indefinite is dirty-brown. Besides, for obtaining intensive black a considerable quantity of color of each color is necessary to suppose on a paper. It leads to paper rehumidifying, and uneconomically.

For the mentioned reasons the black is imported to number of the main polygraphic colors (and in model). She added the last letter in a title of model CMYK though and it is not absolutely normal: With is Cyan (Blue), M — Magenta (Magenta), Y — Yellow (Yellow). The black component is reduced to a letter To as this color is principal, key (Key) in the course of the color press. The number of components (channels) increased to four. That is CMYK — a fourline color model. As well as for model RGB, the amount of each component can be expressed in percentage or gradation from 0 to 255. On fig. 2.9 palette Channels (Channels) for the image in color model CMYK is presented. As you can see, an amount of color channels really equally to four.

View contents of each channel of the image in model CMYK (individually and with different steams). The more channels you make simultaneously visible, the the result will be more dark. As you remember, in this model, unlike RGB, colors mix up субтрактивно.

Thus, model CMYK, unlike CMY, it is possible to name "empirical" model. It describes real colors of colors, instead of theoretical.

Model RGB and model CMYK are hardware-dependent. If it is a question about RGB values of basic colors (and also a point white) are defined by quality of the phosphor applied in your monitor. As a result on different monitors the same image looks unequally. If to address to CMYK here distinction is even more obvious as it is a question of real colors, singularities of printing process and the carrier.

Therefore it is not surprising that eventually there was a task of the description of the colors which are not dependent on equipment, on which these. Colors are received. Unfortunately, to make completely objective determination of color it is not obviously possible. Color is the perceived characteristic depending on the observer and environmental conditions. Different people see colors differently (for example, the artist — differently, than the nonprofessional. Even at one person visual response to color changes with the years.

If color perception depends on the observer and observation conditions, at least, it is possible to standardize these conditions. Such way scientists from the International Commission on Lighting (CIE) went. In 1931 they standardized conditions of observation of colors and researched perception of color at the big group of people. Basic components of new color model XYZ have been as a result experimentally defined. This model it is hardware it is independent, as describes colors how they are perceived by the person, is more exact "standard observer CIE".

Color model Lab used in computer graphics, is derivative of color model XYZ. It received a title from the basic components L, an and b.Компонент L carries the information on image brightnesses, and components and and b — about its colors (i.e. and and b — chromatic components). The component and changes from green to red, and b — from dark blue to yellow (fig. 2.10). As you can see, in the resulted example the chromatic channel b (fig. 2.10,) has enough high contrast because the pyramid has yellow color, and the sky — dark blue. In the channel and (fig. 2.10,) contrast, on the contrary, very low therefore since in the image is not present either green, or red color.

a

In

Brightness in model Lab is completely separated from color. It does model convenient for regulation of contrast, sharpness and other pitch characteristics of the image. It is obvious that model Lab three-channel (fig. 2.11).

Model Lab is difficult enough for practical mastering. It is difficult to us to think of color in its categories: "This color more yellow or dark blue?". Therefore color correction in Lab is not spread widely enough. But value Lab as hardware-independent model has the practical application and in Photoshop. It serves as a kernel of management systems color and is applied (is hidden from the user) at each conversion of color models as intermediate.