IN channels Two types of information can be stored:

• in color channels – information about one or another color component of the image pixels (Red, Green, Blue channels and mixed RGB channel);
• in the additional alpha channel information about the selected area can be stored in the form of a mask.

To select image fragments of complex shapes, use the quick mask mode. In Quick Mask mode, you can create or tweak a selection with a brush—what you paint with a brush in Quick Mask mode will turn into a selection when you switch to Normal mode. This method is convenient because while working on a selection, you can change the image scale, size and shape of the brush, and draw the smallest details.

Attention! Before you start working in quick mask mode, set Foreground color – white, background color – black.

To start working in quick mask mode, select in the top menu. Your image will be covered with a translucent red mask. Anything that is filled with red in Quick Mask mode is unselected. To create a selection, take a brush and start dragging over the part of the image that you want to select. You will see that the brush erases the red mask, the image takes on its natural appearance.

If you accidentally erased the excess, set the foreground color to black, then the brush will restore the mask, painting the image red.

To return to normal mode, select from the top menu Selection – Toggle Quick Mask(uncheck the box).

PRACTICAL WORK "Using a quick mask to select a fragment of an image"

Exercise 1. Quick mask.

Open file 1.jpg Our task is to separate the background from the image of the girl.

First use the tool Free selection, approximately outlining the contours of the girl, then switch to quick mask mode ( Selection – Toggle Quick Mask) and adjust the selection. Return to working in standard mode, invert the selection and remove the background.

Rice. 4.1.

The quick mask is designed for one-time use, as it disappears when the selection is canceled. To be able to use the selection again, you must save its stencil. Masks are stored in special channels. To do this, select Select from the top menu – Save to channel.

In dialogue Channels will appear new channel Copy Selection Mask.

After this, the selection can be removed. If you need to use the selection again, bring up the dialog Channels (Windows – Channels), select the desired channel in the list and click on the button Create a selection from a channel located at the bottom of the dialog Channels.

Exercise 2. Gradient masks.

1. Open files 2.jpg and 3.jpg from the "Rest" folder. Select the “head” using any method known to you, copy and paste it into the photo of water. Bring the “head” to the desired scale and enter quick mask mode.
2. Select a tool Gradient and adjust the color transition from black to white. As you remember, when working with masks, it is not the color that matters, but the tone, which is why the colors for the gradient were chosen this way.
3. Draw a vertical line with the tool Gradient along the entire image. As a result, the drawing will be superimposed smooth transition to translucent red.
4. Return to editing in standard mode. In this case, the gradient mask will take the form of a selected rectangular area. Don't be confused by the fact that only half of the image appears highlighted. Pixels that are not included in the frame will still be partially highlighted with a translucent mask.
5. Do the last simple action - press the key Delete to get a smooth transition between two images, as shown in the figure. If you wish, you can experiment: with repeated presses Delete The area of ​​the selected image will be smaller each time.

Correction of tonal range.

Image toning is the process of achieving proper representation of the darkest and lightest areas of a photograph, as well as clear and balanced midtones. Sometimes when shooting digital camera the tonal balance of the image is disrupted and it may look dull, dark, or, conversely, too bright. When performing tone correction, the main task is to optimize the contrast and brightness of the image.

Color correction of photographs will make the photographs brighter and more saturated, and accentuate individual elements of the photo with color. In addition, color correction makes it possible to correct skin color and eliminate imperfections that may be on the original due to bright sun or shadows.

Tone and color correction commands can be applied to the entire image or to a specific part of the image.

For example, very often you need to “remove red eyes”, or reduce the redness of the face, or “whiten your teeth”...

To change the tone/color of part of an image, you need to highlight using one of the selection tools.

Image toning tools

The main task of tone correction is to ensure the correct distribution of pixel brightness in the image.

The optimal range is one in which the darkest areas are completely black, the lightest areas are white, and the remaining colors are evenly distributed.

To tone an image in the GIMP program, use the commands Brightness – Contrast, Curves and Levels from the menu Color.

An image's tonal range, or key type, can be seen in the image's histogram. In low key images, the main parts are concentrated in the shadows. A high key photograph contains the most detail in the highlights, so mid-tone details are concentrated in mid-key images. A full tonal range image has many pixels in all areas. Correct definition The tonal range helps you choose the appropriate tonal adjustments, and, most importantly, correct a dark or light photo.

To open the histogram palette in Photoshop, go to the main menu tab Window --> Histogram (Window → Histogram).

The following two images illustrate this point. The first has a very limited range. If you hover your mouse over an image you can see its histogram, the tones for this image are clustered in the middle of the range so it has a dull and flat appearance. The second image has been corrected using levels, and as you can see from the histogram, the tonal range is much wider, which greatly improves the image.

Let's open image 1 in Photoshop and try to experiment with correcting the image using the Levels tool. To use this tool, you need to go to the main menu Image --> Correction --> Levels (Image --> Adjustments --> Levels).

Opening this tool, we see that the tones are grouped in the middle of the histogram.

Also, different sections of the histogram vary in height. The height at any given moment indicates the number of pixels at a certain level, so in this case, we see that there are two peaks: a smaller one on the left and a larger one on the right. The one on the left indicates that there are a significant number of fairly dark midtones, and the one on the right shows that there are a larger number of light midtones. At this stage, the shadows and highlights that we see in Figure 2 are completely absent.

So how do we change the image using the Level tool? The easiest way is to move the triangular shaped sliders directly below the histogram. As you can see, there are three of them: black on the left, gray in the middle and white on the right.

As you move the sliders, you will see the input values ​​change in the boxes below the histogram. For example, if you drag the left slider until it touches the left edge of the histogram (gthd[ of the brightness values ​​present) you will see that the value of the left input has changed by 60. This action causes a redistribution of the ACTUAL brightness range across the entire scale due to the fact that regular gaps are formed on the scale.
Likewise, if you drag the right slider to the left until it touches the right edge of the histogram, you will see that the right input has changed its value to 200. For clarity, I have shown the changed position of the sliders with red arrows in the figure.

If we now look at the histogram, we can see that the tonal range has been increased significantly:

Thus, with the help of simple actions using the “Levels” filter, we achieved good results in correcting the tonal balance of the image.

Ticket number 16.

To analyze the tonal content of an image, use the Histogram palette in the Window menu.

A histogram is a special type of graph that shows the distribution of pixels by brightness, from white to black. The vertical lines show the number of pixels that have the same brightness, from darkest (left) to lightest (right). If the histogram is shifted to the left, it is a dark, low-contrast image, and almost all the pixels are dark. If the histogram is shifted to the right, it is a light, low-contrast image, and almost all the pixels are light. A histogram with a peak in the center means that the majority of pixels have average brightness. This means that the picture does not have enough contrast. If the image is high-contrast, the histogram has peaks in the dark and light areas and low pixel density in the midtones. If the image is balanced, it has enough contrast, the pixels are distributed more or less evenly in brightness. Automatic level correction. It is desirable that the histogram contains the full range - from dark to light tones. Photoshop has the ability to automatically correct levels: Image - Correction - Automatic Tone Correction (Shift+Ctrl+L). In this case, the program itself changes the brightness and contrast of the image so as to improve the histogram. Manual level correction. If automatic correction gives a bad result, you can adjust the levels manually: Image - Correction - Levels (Ctrl+L). In the “Input Levels” field, adjustments are made using three sliders - black (the darkest tone), gray (midtones) and white (the lightest tone). If you move the black slider to the right, all pixels located to the left of it are assigned the darkest tone. The white slider “cuts” the histogram on the right - all pixels to the right of it become extremely bright. You can usually discard the "tails" on the left and right sides of the histogram in this way if there are a small number of pixels in them, and the image quality will improve. By moving the gray slider, you can darken or lighten the midtones. Don't forget to check the Preview checkbox - this allows you to immediately see how the image will change. This is how you edit the overall brightness (RGB channel) right away. Typically, the best results are obtained if you adjust each channel separately: red (R), green (G) and blue (B). To do this, you need to select the desired component in the “Channels” list and perform correction using three sliders. Then we move on to the next channel, etc. Contrast and brightness. Setting up many devices with a screen (TVs, monitors) is done with two controls that change the brightness and contrast of the image. Photoshop also has the ability to change these characteristics of a drawing.

Auto contrast. Automatic contrast adjustment is performed using the menu item Image - Correction - Auto Contrast (Alt+Shift+Ctrl+L). Manual correction.

For manual correction, you need to open the Image - Correction - Brightness/Contrast window, which contains two sliders. Curves. This image is very dark overall, but the light tones are well done and don't need to be altered. However, you need to lighten the dark and mid tones. It is convenient to perform such complex adjustments using curves (menu Image - Corrections - Curves, Ctrl+M keys). The horizontal axis shows the brightness before the transformation, and the vertical axis shows the brightness after the transformation. At the beginning, the curve represents the diagonal of a square - the brightness of the pixels does not change. By clicking the mouse, you can set points on the curve, which are then dragged to the desired position. To remove an unnecessary point, you need to drag it outside the graph. It is convenient to immediately observe the changes being made on the histogram; to do this, you need to position the windows so that you can see the Histogram window.

If the curve in some place goes above the diagonal, these tones are lightened; if below, they are darkened. A steep slope of the curve indicates an increase in contrast, a flat curve indicates a decrease in contrast. For example, the curve shown in the figure makes the following changes: the brightness and contrast of light tones are left unchanged, for this purpose the right control point on the diagonal is set on the curve; the brightness of dark and midtones is increased (the curve is above the diagonal); the contrast of dark tones is increased (the slope of the curve is greater than the slope of the diagonal); midtone contrast is reduced (the slope of the curve is less than the slope of the diagonal). Just like for levels, curve correction can be done separately for each color channel (red, green and blue). Light and shade. If the image has increased contrast, this can be seen in the histogram. In such cases, it is useful to use the Lights and Shadows command, which allows you to separately adjust the light and dark areas, as well as the contrast of the image. Correction modes are automatically set for shooting against the light or with flash. Sometimes use manual settings allows you to improve the result. Correction of individual areas. All previous methods made it possible to change the brightness and contrast of the entire image. However, sometimes you only need to correct certain areas of the image without affecting the rest. Three tools are used for this purpose, which are associated with one button in the Tools palette and the O key: Dodge brightens the areas through which the brush passes, Burner shades areas, Sponge allows you to increase or decrease the color saturation. These tools are used to highlight important objects, increase or decrease contrast in certain parts of the drawing, and add light or shadow to direct the viewer's attention to the desired object. Unlike the Brightness/Contrast command, these can be adjusted to only affect highlights, shadows, or midtones. To do this, select the desired option in the Range drop-down list on the tool properties panel. For example, in order to increase contrast, you need to lighten light tones and darken dark ones. Second important parameter- Exposure - determines the strength of the tool’s impact on the image. Professionals recommend working with an exposure of no more than 10%, so that the changes made are smooth and the result looks natural. A brush is used to lighten or darken. Its main parameters - diameter (in pixels) and hardness (from 0 to 100%) are set in a special window that appears when you press the button. Typically choose a soft brush with a hardness of less than 50%. It should be noted that the Dodge and Burn tools are better suited for editing black and white (grayscale) images. When correcting color images, Brighten (if used in excess) “washes out” light colors, making them white. In contrast, Darkener may result in gray spots in the image.

In this lesson we will talk about what a histogram is and what useful information You can extract it from it for further work with the image.
You can see the histogram of the image by selecting from the menu Window - Histogram(Window - Histogram).

At first glance, it is not clear enough. A person far from medicine understands the same amount when he sees a cardiogram or an encephalogram. But, unlike medical graphs, with a histogram everything is much simpler. It serves as the main tool for objective assessment of the technical parameters of a photograph, along with the palette Info.

A histogram graphically shows the distribution of image pixels across brightness levels. The higher the histogram bar, the more pixels of a given brightness are present in the image. You can study the histogram directly in the palette, or by calling the command Levels(Levels). To do this you need to click CTRL+L.

The histogram can be divided into three areas: the leftmost one is called the Shadows area, the rightmost one is called the Highlights area, and the central part is called Midtones.

It is also customary to distinguish quarter gradations of brightness: light, quarter tone, half tone, three-quarter tone, shadows. On the black color density scale, 0, 25, 50, 75, 100%, respectively. In Photoshop, this gradation is applied in the dialog box Curves Curves).

Basic information about the image is obtained by selecting in the field Channel(Channel) values Glow(Luminosity). In this case, only the brightness component is displayed on the histogram. This field also allows you to select other channels to display (red, green, blue, etc., depending on what color space you are working in).

In line Average(Mean) specifies the weighted average brightness level of the image pixels, which is obtained by multiplying each brightness level by the number of pixels at that level, and then dividing by the total number of brightness levels. The higher the weighted average, the higher the lightness of the image.

In line Deviation(Std Dev) indicates the statistical (standard) deviation of tone levels. The greater the deviation, the higher the contrast of the image.

In line Median(Median) is the value of the tone that splits the histogram sample into two equal parts. This tone is the midpoint of this histogram. Half the sample lies on one side of the median, half on the other. The proximity of the median value to the deviation value indicates a uniform, balanced tone of the image.
In line Pixels(Pixel) shows the total number of pixels in the image.

In line Counter(Count) - the number of pixels of a given tone or tonal range (at the point where the mouse cursor is placed on the histogram).

In line Percentile(Percentile) shows the percentage of pixels to the left of the cursor.

On line Level(Level) we will go into more detail. It shows the level of lightness of the tone. The data from this line is used to place control points on the curves, which allows you to make very subtle and precise image corrections (you will learn about this in one of the following lessons). You can also get data for a certain range of tones from this line. To select it, click the left mouse button and drag the cursor over the desired area of ​​the histogram. Don't release the mouse button.

The selected area of ​​the histogram will turn white, and in the line Level The start and end values ​​of the range are displayed.

Now let's look at how to determine some types of defects based on the shape of the histogram.

1. Underexposed photo.

The pixel fill area of ​​an underexposed photo is shifted to the left. Images with this defect can be corrected well, but noise in the shadows may increase. The exception is severely underexposed photographs or photographs taken against the sun. The dark areas of such images become almost black, color information is lost in them, so it is problematic to restore images with such a defect.

Photos taken in the evening or at night, as well as photos of initially dark objects where there are no bright areas, are not considered underexposed (provided they adequately depict the appropriate range of tones).

2. Overexposed photo.

The case is exactly the opposite. In this case, the histogram lacks information in the shadows and quartertones. In the highlights area, the histogram comes close to the right edge, indicating that the brightest areas are being clipped.

Artificially stretching the tonal range to its fullest extent leads to an increase in white areas, which upsets the balance of colors. In addition, in overexposed areas there is completely no information about color, i.e. they are pure white in color.

Correcting overexposed photographs is one of the most difficult tasks in digital photography. Typically, heavily overexposed photographs are considered damaged.

It is possible to restore colors in light areas only when shooting in RAW format, and then only with overexposure of no more than 0.5-1.5 stops.
You should also distinguish between underexposed photographs and scenes where there are practically no shadows, for example, high-key portraits, shooting light flowers on a light background, winter landscapes.

3. Weak contrast.

The histogram of a low-contrast image does not have pronounced peaks; its area is limited by a smooth curve. Although, at first glance, the photo shows the full tonal range, the overall contrast is clearly insufficient, which reduces the expressiveness of the image.

4. Excessive contrast (posterization).

With excessive contrast, a loss of brightness and color information occurs, which is expressed in jaggedness, the appearance of breaks and gaps in the histogram. Such images are difficult to correct.

5. Normal histogram.

Note the full tonal range and the presence of several sharp peaks. They indicate good elaboration of individual objects and a sufficient level of contrast. Of course, the nature of a normal histogram depends on the subject of the shooting and the purpose of the publication. In most cases, it is desirable to have a full tonal range and pronounced accented areas.

Image histogram

Tone correction consists of redistributing light and shadow between pixels, that is, adjusting the brightness and contrast of the image. This can be done on both grayscale and color images, but we'll start with halftone images, which are easier to learn.
The quality of a halftone image can be determined by the brightness histogram. Since a halftone image consists of shades of the same color, all its pixels differ from each other only in brightness. Image histogram is a graph where brightness levels from 0 to 255 are plotted along the horizontal axis, and the number of pixels in the image is plotted along the vertical axis. The part of the range that is used in an image is called its tonal range.
The leftmost point of the histogram corresponds to zero, and the rightmost point corresponds to the maximum possible brightness. The wider the tonal range, the more detail an image can convey and the higher the quality. Conventionally, the tonal range is divided into three parts. The left part corresponds to the dark parts of the image, the right part corresponds to the light parts, and in between are the midtones. An ideal image contains pixels of all shades. In the photograph in Fig. 9.1 has practically no light or dark tones, it is too gray. To correct it, it is desirable to expand the tonal range.
To see the histogram of the image and perform range correction, run the command Window ~ Histogram . In order to transform the dialog box to a more informative view (as in Fig. 10.1), select lines in the palette menu Expanded view And Show statistics . The following information is displayed below the histogram:

• Average - average brightness value;
• Deviation - average deviation from the statistical average;
• Median - the middle of the tonal range of the image;

Pixels - the number of pixels in the entire image or in the selected area.

On the right, information is displayed about the place in the histogram where you are holding the pointer:

• Level - brightness level at the pointer location;
• Number - number of pixels with a given brightness level;
• Interest - the number of pixels with levels not greater than the current one as a percentage of the total number of pixels in the image.

You can view statistics for a range of brightnesses. To do this, click at the starting point of the range and drag the pointer along the horizontal axis. The range will be highlighted as the pointer moves. All this time, the right side of the display displays current information about the selected range. In line Level you see two values: initial and final levels allocated range.

Figure 9.1. Gray image brightness histogram

Exercise 9. 2.

One of the methods of tonal correction is stretching the tonal range. To do this, the lightest and darkest tones that are represented by too few or no pixels are discarded on the brightness axis. The darkest of the remaining tones (called the black point) is replaced with black (with zero brightness), the lightest is replaced with white (called the white point). The brightness of all intermediate tones is recalculated using the old curve. To preserve image detail, you must manually adjust the midtones.
To configure, run the command . A dialog box will appear in front of you (Fig. 9.2, in the rollout Channel You can select a custom channel or the top line with the name of the color model (all channels): RGB, Red, Green, Blue, Luminosity, Color. Let's look at the setup using a practical example.

1. Open an image Palace.jрg from the Lesson 9 folder (Fig. 9.2) and run the command Image ~ Correction ~ Levels. Since this is a grayscale image, there is no need to select a channel.
2. In the fields Input levels you see the values ​​of the input levels, that is, the boundary brightness levels. At the beginning of the settings, they are equal to 0 and 255. In the middle field - the brightness of the average tone, it is measured in arbitrary units and can vary from 0 to 10. By default, it is 1.
3. Check the box Preview , to see the changes taking place.
4. First, let's set the black point of the image. Click on the left slider (it's black) and drag it to the right, to the place where there is already a noticeable number of pixels before the input level - 25 . The entire image darkened slightly. Instead of moving the slider, you can enter desired value to left field Input levels.
5. Now set the white point of the image by moving the right white slider to the left, as in Fig. 10.2 on the left, up to the input level value - 220 . The image brightened again and had more contrast than before.
6. Now you can adjust the midtones a little without touching the edge of the range anymore. To do this, move the middle gray slider in different directions and select its optimal position.
7. Click OK. Open the window again Levels and see what the image histogram looks like after correction (it stretches across the entire range).
8. Save as name Tonal Range Stretch and close.

Figure 9.2. Tonal Range Correction

You can stretch the range automatically by clicking the button Auto window Levels. Automatic correction is always performed in the midtones, that is, the range is cut off on both sides. For color images, this type of correction is performed for each channel. At the same time, the remaining channels are automatically adjusted so that the color of the image does not change.
Automatic correction can be performed without entering this window. To do this, select the command Image ~ Correction ~ Auto Levels .
On the right side of the levels window you see three buttons. With their help, you can specify white, black and gray points directly on the image. To do this, you must first click on the corresponding button, and then on the darkest or lightest place in the image. The middle button (gray dot) only works in color images. It allows you to specify a neutral gray tone.
To cancel the entire setting and return to the beginning, press Alt. Button Cancel, which you are using will be replaced with a button Restore. If the tonal range is significantly stretched, gaps may appear in the histogram (the histogram becomes like a comb). There's nothing wrong with that, as long as they're not too big.

Exercise 9.3. Narrowing the tonal range

By stretching the range, we increased the contrast of the image. Sometimes you are faced with the opposite task - reducing contrast. This is especially necessary if the image is intended for printing. In this case, very dark and very light areas in the images turn out poorly. You can also use the bottom slider to adjust the tone. Output levelswindow Levels.

1. Open an image Na6ezhnaya.jрg from the Lesson 9 folder (Fig. 9.3) and select the command Image ~ Correction ~ Levels .
2. The image is quite contrasting due to the black outline of the monument. To lighten the darkest parts of the image and darken the lightest ones, move the black and white sliders Output levels, as in the dialog box in Fig. 9.3 (33 and 236).
3. The image has become less contrast. Adjust the midtones with the intermediate slider to make the relief of the monument more distinct. Click OK.
4. Save as a name Narrowing the tonal range and close.

Figure 9.3. Narrowing the tonal range

Exercise 9.4.

For correct settings It is important to accurately determine the black and white points of the image. You can determine the black and white points in the window Image ~ Correction ~ Levels .
Move the right white slider to the left until the entire image is white except for the darkest parts of the image. Remember these places. This is the black point of the image. Next, move the left black slider to the right until almost the entire image is black except for the lightest highlights. Remember these places too, this is the white point of the image.

1. Open the document Palace.jрg from the Lesson 9 folder. You are already familiar with it. We'll adjust this image again using anchor points
2. To do this, run the command Image ~ Correction ~ Levels . Identify black and white dots. The black dot is in the branches of the tree, and the white dot is on the road strip in the foreground. Remember these places.
3. Select the black eyedropper and select a black point, and use the white eyedropper to select a white point. You will get (almost) the same result as in Exercise 9.1.
4. You can do it interesting options, if you choose other places as the black and white points (by simply clicking at random in different places).
5. Save as name Correction with black and white point detection and close.

Exercise 9.5. Adjusting Brightness Levels Using a Tone Curve

Another way to change the characteristics of halftone images is to adjust the tone curve. Working in the window Levels, you could only influence the placement of darks, highlights, and midtones. In the window Curves you can selectively change the brightness at individual points of the histogram (Fig. 9.4).
To open this window, select the command. This window contains the tone curve. The horizontal axis shows the input brightness levels (initial), and the vertical axis shows the output brightness levels (after correction). By default, the graph is a straight line X = Y, that is, the output level at all points is equal to the input level. To display the advanced mode, click on the button Curve Display Options
If you move the pointer along the chart, the coordinates of the pointer on the chart are displayed below: Input levelAnd Output level. Below the curve and to the side of it are gray scales that show the location of dark and light tones on the graph. For the RGB color model, darks are at the bottom left ( brightness 0), and light ones ( brightness 255) - top right. For the SMUK model, the reverse arrangement is used; you can switch modes using the checkboxes Light, Pigment ~ Ink under the scale in advanced mode.
The field in which the graph is drawn is marked with a grid. To make it smaller, click on it while holding down the key Alt or click on the corresponding button to display the grid below the scale. In the default dialog box, an image histogram is superimposed on the scale with the curve. At the bottom of the dialog box, you can remove the histogram blend mode.
For color images in a scroll Channel You can select a custom channel or the top line with the name of the color model. In the latter case, the total brightness of all channels will be adjusted. When you adjust one color channel, the others are adjusted automatically so that the color of the image does not change.
At the top of the dialog box in the rollout Blanks You can select standard tone correction presets. When selecting individual modes, image tones are automatically corrected.

1. Open an image Curve correction.jpg from the folder Lesson 9.
2. Select a team Image ~ Correction ~ Curves . Turn on advanced mode with the button Curve Display Options . Turn on the RGB-specific gray scale mode, as in Figure 9.4.
3. Let's repeat the operations in previous exercises. First, let's expand the tonal range. To do this, click on the top right point of the line (the dark colors should be at the bottom). The pointer will turn into crossed arrows. Move the point to the left one cell. The image becomes lighter.
4. Click on the lower left point of the line and move the point to the right, also one cell. The contrast of the image increases as the straight line becomes steeper.
5. Now let's narrow the tonal range by cutting off the darkest and lightest places. To do this, move the top point down and the bottom point up. At the same time, the slope of the line decreased and, as one would expect, the contrast also decreased.
6. Don't cover both the image and the window Curves.

Exercise 9.6. Changing the Shape of the Tone Curve

This window has almost the same cnopki as in the window Levels. Using cnopki Auto You can automatically stretch the range in both directions. cnopki with eyedroppers allows you to specify black, white and gray points (the latter for color images only) directly on the image itself. When you press the Alt key, a button appears Restore to return to its original state.
Next we move on to corrections that cannot be done by adjusting the levels. There are certain places in every image where it is especially important to change the contrast or brightness. To achieve this, you need to move individual points on the curve, changing the brightness for a specific range of tones.
This can be done in two modes, switching between them using the buttons: smooth curve mode, in which only individual points are moved, the curve between them is automatically curved so as to remain smooth; a freehand curve drawing mode in which the entire curve or portion of it is drawn with a pencil. The curve in this case can be of any shape.
Let's consider the first mode, since it is more gentle. To fix the brightness of some part of the curve, click in this place on the graph. A point will appear on it, and with further automatic changes to the curve, this place will be fixed.
To change the brightness of any interval, click in the middle of it and drag the created point up or down. In total, you can create up to 16 points on the curve; their position can be adjusted later. You can activate several points at once by clicking on them while holding down the key Shift. This will allow you to drag an entire curve segment.
To delete an unnecessary point, click on the button Del. The end points of a tone curve cannot be deleted. To determine the location of individual tones on the curve, click and move the pointer over the image - a round dot will move along the graph. It marks the range of the curve in which the brightness corresponding to that detail lies. Now let's put these techniques into practice.

1. Return to the image Correction curve.jрg with an open window Curves- Fig.9.4.
2. Move the eyedropper-shaped pointer over the places you like, for example, over the model's face. It lies in the range 160 -255. Click at these points on the curve to lock them.
3. After this, you can move the remaining sections of the curve; the changes will not particularly affect the face.
4. You can try other options, for example, as in fig. 9.4, - the result will also be quite good.

Figure 9.4. Adjusting the Tone Curve

By switching to freehand curve drawing mode, you can freehand draw a curve on any area. This is done in the same way as when drawing with a tool Pencil, that is, moving the pointer with the mouse button pressed. The old piece of the curve in this place is erased. You can even draw the entire curve by hand. To then smooth the resulting curve, click the button Smooth .

Independent work

Try drawing a curve using the freehand drawing mode with different humps and valleys and see how interesting it can change the image. Check out the different standard tone curve correction modes in the rollout 3preparations dialog box. Save under name Independent work..

Control questions:

1. What is an image histogram?
2. What is tonal range? Why is it necessary to expand and narrow the tonal range?
3. What is the black, gray, white point of an image? Why is it necessary to define them?
4. What is a tone curve? What is it used for?