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Automatic image correction: myths and reality. Should You Use Photoshop's Auto Correction Features? Complete solutions for image processing

Color correction is essential component processing of digitized images. Especially often the need for it arises during the prepress preparation of photographs: film negatives tend to fade over time, shifting the overall image gamut towards blue or red colors. Digital cameras also do not guarantee flawless quality due to uncontrolled errors. manual setting balance. Of course, modern graphic editors have the necessary tools to correct color errors manually, but this is not very effective when processing documents in stream. Fortunately, there is whole line low-cost solutions from third-party manufacturers that allow you to automate the process of color correction of images as much as possible.

AutoEye 2.0 (AutoFX Software)

The AutoEye 2.0 package is new version popular software product designed to improve the quality of digital images by restoring color detail and enhancing clarity. As before, AutoEye 2.0 is available either as standalone program for Windows platforms and Macintosh, or as a plugin for the most common graphic editors: Adobe Photoshop CS, Jasc Paint Shop Pro, as well as Corel Photo Paint and CorelDRAW 9.0. Although all these programs have built-in image correction tools, AutoEye 2.0 compares favorably with them due to the use of unique proprietary Intelligent Visual Imaging Technologies (for example, the plug-in does not rely on traditional curves and a histogram in its work), allowing you to solve the same tasks in a simpler way. way, as well as automate as much as possible and, therefore, speed up their implementation.

Thanks to the use of "intelligent" tools, the developers managed to simplify user interface programs. All controls are grouped into three sets: Enhancement (image error correction), Color (color adjustment) and Creative (artistic processing), and a single panel is enough to control all the changes made to the image, which is undoubtedly much more effective than traveling through numerous dialog boxes and branched menus.

The Color Controls mode, in turn, is responsible for adjusting the color of the image. Through the use of advanced blending algorithms and correction tables, the program is not only able to restore faded colors when shooting or scanning the original, but also allows its user to change their original gamut - again, with just two or three mouse clicks.

To save preliminary results of work without making changes to the original file, AutoEye 2.0 allows you to save the current settings in separately stored profiles. The program accepts files in .psd, .tiff, .bmp, .jpg, .gif, and .png formats as source documents. If the Adobe Photoshop .psd format is selected for processing, information about the layers is saved.

AutoEye 2.0 is priced at $129. A demo version can be downloaded from the developer's website http://www.autofx.com/demo_center.asp .

AliveColors 1.1 (AliveColors)

AliveColors 1.1 is a convenient and easy-to-use utility entry level, which has extensive capabilities for color correction and retouching of digitized images "with one button". Efficiency is achieved through the cumulative use of a number of procedures hidden from the user by a simple visual interface.

The AliveColors 1.1 arsenal includes eight built-in color correction functions, as well as a set of traditional tools for "mechanical" image editing, including tools for selecting, cropping, reversing and inverting the active layer. Although the user has access to almost all procedural parameters for more fine-tuning, in most cases the program manages to restore image quality automatically (Automatic correction by Channels and Automatic correction by Brightness functions).

Along with document-wide automatic color correction, AliveColors 1.1 allows for more subtle editing, such as sharpening, creating a blur effect, or selectively replacing colors in a selected area of an image. It is noteworthy that the results of all operations performed are displayed in real time in the preview window, and the history saving function allows you to go back a few steps.

AliveColors 1.1 supports the TWAIN protocol, so images can be loaded into the program directly from a scanner or from a digital video camera connected to a computer. The only drawback could be an overly limited set of raster file formats known to the program (there are only four of them - .bmp. .tiff, .jpg and .png), but this limitation applies only to the stand-alone version of the utility, while AliveColors 1.1 is also available as a plugin for Adobe Photoshop, Corel Photo Paint and Jasc Paint Shop Pro. Along with the full version, the developers offer it free option with reduced functionality (the automatic color correction mode is turned off in it).

The price of AliveColors 1.1 is 27 euros. A demo version can be found on the developer's website at http://www.alivecolors.com.

Color Mechanic Pro (Digital Light & Color)

Color Mechanic Pro is a plug-in for Adobe Photoshop and Photoshop Elements developed by Digital Light & Color, which includes a fairly powerful and convenient mechanism for correcting and editing the color of an image. Unlike most programs of its class, Color Mechanic Pro operates with the HSL color space, and its operation is based on algorithms for separate channel editing with their subsequent connection. Selective analysis and approximation calculations are performed in a fully automatic mode. In fact, the role of the user comes down to choosing an object for correction (color control is carried out using HSL hexagons and fine-tuning sliders); at the same time, the plug-in supports selection areas created by standard Photoshop tools.

In addition to the "full" version of the plugin, the user is offered its lightweight version of Color Mechanic Standard. The main difference between them is that in full version editing is available for both RGB and CMYK images in 16 bits per channel, while in the simplified version this is only available for CMYK. In addition, the full version interface has several auxiliary tools, as well as an unlimited command stack to return to the previous state.

The price of Color Mechanic Pro is $50. A demo version (it does not allow you to save the correction results) can be downloaded from the developer's website at http://www.colormechanic.com.

Digital ROC Professional (Eastman Kodak Company)

The DIGITAL ROC Professional plug-in is sold under the trademark Kodak, one of the veterans of digital photography, but the range of potential users of this program is by no means limited to owners of digital cameras. On the contrary, this tool is useful to anyone who, on duty or in his spare time, has to face the need to quickly and efficiently color correct a problematic image. The plugin provides the ability to automatic recovery document and then manually adjusting the color balance for optimal results.

DIGITAL ROC Professional's algorithms analyze the color gradients of the uploaded image to detect aliasing or general hue imbalance caused by poor original quality or a hardware calibration error. Based on the results of this analysis, the program generates compensating hue curves in each of the color channels (while supporting 16-bit processing). More fine tuning brightness, contrast and color gamut can be subsequently carried out manually - for this, the plug-in dialog panel provides a preview window that is updated in real time.

DIGITAL ROC Professional works with files from a variety of sources, including digital cameras, flatbeds and slide scanners. In the latter case, the plug-in has additional built-in tools to improve image quality by suppressing traces of film grain.

The plugin is compatible with all Adobe versions Photoshop since 5.0, Jasc Paint Shop Pro 7.0 and later, and other applications that support the model Adobe plugins. The price of DIGITAL ROC Professional is $50, and you can find a demo version of the program on the developer's website at http://www.asf.com.

iCorrect EditLab (Pictographics International Corporation)

iCorrect EditLab is a powerful professional tool for automatic color correction of images, available as a plug-in for Adobe Photoshop and a number of other most popular graphic editors. The program mechanism is focused on full color correction on the scale of the entire document, based on automatic analysis of the color information contained in the file, recognition of predefined sets of shades (for example, the color of the sky, foliage, human skin, etc.), as well as user-specified parameters and current control settings Photoshop color(or other "mother app").

iCorrect EditLab provides a fully automatic mode of operation, however, at each of the color correction steps, the user has the opportunity to agree with the option proposed by the computer or make his own edits to it. The entire editing operation consists of four successive stages. At the first stage, the program balances on a neutral hue, determining those areas of the image that should be painted in gray of medium intensity, thereby eliminating the effect of the so-called color cast. The second step is to find the limit points for white and black. Next, iCorrect EditLab adjusts the saturation of the hues, as well as the contrast and lightness of the image. The fourth, final stage is the most difficult - on it the program restores the natural color of individual shades.

iCorrect EditLab costs $100. You can find a demo version of the plugin on the developer's website at

As I said, you do not need to know how these tools work, but you need to know something else - in what cases to get best results preference should be given to one tool or another.

To make it a little easier for us to deal with this issue, let's slightly repeat the theory. As you know, the whole variety of colors displayed on a computer monitor is generated by shifting the three primary colors - red, green and blue.

White is obtained by mixing red, green and blue in equal proportion and full intensity. Black is total absence all three primary colors. Yellow, for example, is made by mixing red and green. Mix red and blue and you get magenta, while green and blue together make turquoise. Apply red, green, and blue shifts in varying proportions and their hues in every possible hue, and you end up with millions and even billions of colors.

Photoshop blends these three primary colors using color channels. One channel for red, another for green, and a third for blue. We can find these color channels in the Channels panel, which, by default, is nested in the same stack as the Layers panel. Click on its tab at the top of the panel group to open it:

Open the channel panel by clicking on the appropriate tab.

In the panel we see red, green and blue channels, plus a fourth RGB channel located at the top of the panel. Don't let the RGB channel fool you, it's not really a channel at all. RGB stands for "red, green and blue" and is simply a combination, a composition of the red, green and blue channels working together to give us a full color image.

If you look at the preview thumbnails of the red, green, and blue channels, you'll notice something that might seem a bit surprising - those color channels aren't actually in color at all! Instead, each one is a halftone image. In fact, if we take a closer look at them, we can see that the black and white image of each channel is different from the other. To preview how each channel looks in the document, simply click on it. For example, I'll click on the Red channel to select it:

Red channel selection.

With the red channel selected, the full color version of my image in the document is temporarily replaced with a grayscale version. So what does a black and white image mean when the red channel is active? This is how Photoshop shows the intensity of the red in the picture - the brighter the area, the more red is added to the full color version, while the darker areas have less saturated red. Areas of pure white in a black and white image have red at its full intensity, while areas of black have no red at all:

Red channel preview. Bright areas contain more red than dark areas.

To see what the green channel looks like in the document, I'll click on it in the channels panel.

This action will temporarily turn off the display of the red and blue channels, showing me only the green channel in the document. Here we see another grayscale image, but it is slightly different from what we saw with the red channel. This is because the intensity of green in different areas of the photo is naturally different from the intensity of red. Again, the brighter the area, the more intense the green in it, while the darker areas have less saturated green. Any areas of pure white have green at full intensity, while areas of pure black have no green at all:

Green channel preview. Lighter areas = more intense green, darker areas = less green.

If we now look at the black and white image of the blue channel, then it will also be different from the others and work in exactly the same way. My photo contains a lot of blue (or any other color that uses blue as its main ingredient) so the blue channel looks darker overall than the red and green channels:

Blue channel preview. The lighter the area, the more blue is involved in the color blend in the full color version.

So we've learned that Photoshop mixes the red, green, and blue color channels to reproduce all the colors we see in the image. Now, based on this, let's try to figure out which of the three tools under consideration is better to use when. Each of the three automatic commands manipulates the color channels differently, producing different results. In the following, I will briefly describe how each works, before we look at them in action.

The Auto Contrast tool is the most basic and straightforward of the three discussed in this tutorial. When we select it, Photoshop analyzes the composite of all three color channels (in other words, it treats all three as if they were one black and white image) and simply converts the dark pixels to pure black, brightens the light pixels to pure white, and redistributes all other tonal values in between. The result is an image with improved overall contrast. It's important to note that because it treats all three color channels as one composite image, Auto Contrast doesn't change the colors in the image. It just boosts overall contrast, making it a good choice for images that don't suffer from any color issues.

Auto Tone is similar to Auto Contrast in that it also darkens dark pixels to pure black, brightens light pixels to pure white, and redistributes all other tonal values between them, but it has one major difference. He does this not on the basis of three channels mixed into one, but on the basis of each channel separately, which means that the red, green and blue channels will be adjusted individually as well. We know that Photoshop uses the lightness values in each individual color channel to determine how much of each color to mix in the full color version, so by changing the color channels independently, we will change the colors in the full color photo because brightness values in channels changed. This means that, unlike Auto Contrast, which does nothing more than increase the overall contrast, Auto Tone changes the colors in the image at the same time as increasing the contrast. If an image has an unwanted color cast, Auto Tone may be able to fix it.

Auto Color is similar to Auto Tone. It also darkens dark pixels to black and lightens bright pixels to white on a per-channel basis, so that the red, green, and blue channels will be adjusted separately and independently. But Auto Color goes one step further. Instead of just redistributing all the tonal values between them, it attempts to correct any unwanted color cast by neutralizing the midtones in the image. This is usually (but not always) done by Auto Color the best choice to automatically correct contrast and solve color problems at the same time.

In the next article I will tell you how to use the tools correctly and effectively. auto tuning images.

With the help of this lesson, you can significantly improve the work of the team Automatic color correction (Auto Color). By doing this once, you will have a much more effective tool at your disposal. In addition, you will learn new things about tools such as Pipette (Eyedropper) And Curves (Curves).

Let's start the lesson.

Step 1. Opening the Image

Let's say you've opened an image that needs color correction. But time to fine-tune with Curves (Curves) you do not have. Here you can see that the shooting was carried out under artificial lighting with lamps. daylight, which gives the image a green tint.

Step 2. Making auto-correction

Select from the menu Image - Automatic color correction (Image - Auto Color) or click Shift+ ctrl+ B.

The use of this command is not accompanied by the appearance dialog boxes, the program itself tries to balance the colors of the image. Sometimes a completely acceptable result is obtained, sometimes the image becomes even worse than the original. Next, we will look at two ways to improve the performance of this tool.

Step 3. Improving the result

One way to improve the result is to go to the menu immediately after using the command Editing - Loosen: Auto Color Correction (Edit - Fade: Auto Color) or click Shift+ ctrl+ F.

In the dialog box that appears as shown in the figure below. Drag the slider to the left until you get an acceptable result. You can also change the blend mode, for example Multiply will help to darken the image, mode Lightening (Screen) brighten, and so on.

Step 4. Set up auto-correction

There is another, in my opinion, better technique that allows you to change the parameters of this command even before it is used. It turns out that Photoshop has the ability to adjust the automatic color correction, but these settings are located where most of us do not even look. To access them, you need to open the command dialog Curves (Curves) or Levels (Levels) . You can do this by clicking CTRL+M or CTRL+L.

Then press the button Options. A dialog box for setting correction parameters will appear on the screen.

Select options Find dark and light colors And Snap to neutral midtones. You also need to check the box next to the option Save as default. Click OK. Now the settings you have made are saved.

But that is not all. Now you need to specify the values of the black, white and gray points and adjust the tool parameters Pipette (Eyedropper), which is used in many commands and tools Curves (Curves), Levels (Levels), Selection - Color range (Select - color Range) etc. This is what we will do in the next steps.

Step 5: Adjusting the Black, White, and Gray Point Values

Adjust the black, white and gray point values. Double click on the black eyedropper. In the dialog box that opens, enter the values R = 20, G = 20, B = 20.

Press Enter. Similarly, double-click on the eyedropper corresponding to the white point and enter R = 240, G = 240, B = 240.

For an eyedropper corresponding to a gray point, the values of all three colors will be 128.

Now click the button again Options and keep the default values.

Step 6: Set Up the Eyedropper Tool

Setting up the tool Pipette (Eyedropper). Select it from the toolbar. This tool not as simple as it seems. It is used for color sampling, or for analyzing a specific area of an image, depending on which command it is used in. By default, the size of the sample taken by the pipette is 1 pixel.

But at the same time, for example, the color of a patch of skin or white snow is actually determined not by one, but by several pixels of different colors. If you magnify a portion of the image a lot, you will understand what I am talking about. From this follows the conclusion that if the color of only one pixel of the area is taken into account in the selection of color, then the probability of error is high. To make such errors less frequent, you need to set the sample size to 3x3 pixels.

Then all commands using the tool Pipette(eye dropper), will receive averaged data already from nine pixels of the area. This greatly improves the accuracy and efficiency of the work.

Operations for adjusting black, white and gray color, called targets, can also be performed in the settings dialog box. The setup is done in exactly the same way.

I deliberately suggested two methods for you, try both and choose the one that you like best.

Step 7. Finishing the setup

So, we have finished setting up the command. Now we have a much more convenient and efficient tool to work with. In addition, when the button is pressed Auto in the command dialog Curves or Levels the image will also be applied Automatic color correction. Also, you now know how to manage the settings of these tools. And here is the image that came out after the correction.

I wish you creative success!

Image Adjustment in Photoshop

Sofya Skrylina, teacher at the Art training center, St. Petersburg

CompuArt No. 12'2011 discussed methods for diagnosing color shift and some Photoshop tools for color correction of the image. In this issue, we will continue to remove color shift using other tools, as well as analyze situations when it is more appropriate to use the Lab model instead of the RGB model.

Options

Dialog window Options(Variations), in addition to removing the color shift, allows you to adjust the tonal balance of the image. In the upper part of the window there are two thumbnails - the original image and the result of the adjustment. The following are examples of correction, to apply a particular option, you just need to click on its thumbnail (Fig. 1). Using the slider, you can set the accuracy of correction, and using the switches, change the saturation of the image or the area of correction: Shadows(Shadows) midtones(Midtones) Sveta(highlights).

If the window is reapplied, then before the correction, you must reset the previous settings by clicking on the thumbnail of the original.

This window is called by the command Image(Image) -> Correction(Adjustments) -> Options(Variations). On fig. 2 shows an example of eliminating red excess using this window.

Rice. 2. An example of removing a color shift using the Options dialog box (on the left is the original image)

Applying a Dialog Box Pick up color

Command Pick up color(Match Color) allows you to remove the color shift in one image based on another image. It is used when it is necessary to process a series of photographs taken under the same conditions. In this case, it is enough to balance the colors on one image, and process the rest with this command, taking the image with the removed color shift as the source. This command It also comes in handy for balancing the colors of different images combined in the same project so that you can use the same colors that match well.

To match the colors of the two images, you must perform the following manipulations:

Open both files in Photoshop, go to the window of the photo to be corrected (Fig. 3).
Run command Image(Image) -> Correction(Adjustments) -> Pick up color(match color).
From the drop down list A source(Source) select an image whose colors will be used to replace the colors in the photo with a color shift (Fig. 4).
Adjust correction parameters:

using the slider Luminosity(Luminance) — brightness of image pixels;
slider Color Intensity(Color Intensity) - color saturation;
using the slider Let loose(Fade) - partially restore the original colors of the image;
when checkbox is checked Neutralize(Neutralize) the program will try to determine which shades of the image were neutral and keep them that way. This operation does not correctly determine the neutral color in all cases.

The result of the correction and the original photograph are shown in fig. five.

Rice. 5. An example of eliminating excess red color using the Match Color dialog box (on the left is the original image)

Quick color shift correction

In addition to tools that have a large number different settings, Photoshop offers quick adjustment tools. In relatively simple situations, they will help you get a satisfactory result fairly quickly. Consider tools for automatic color shift correction.

Auto Correction Tools

Automatic color correction is performed in the dialog box Levels(Levels) or Curves(Curves) at the click of a button Auto(Auto), and its setting is in the dialog box opened by clicking on the button Parameters(Options), - fig. 6.

Three pipettes can be used for color correction: black, gray and white. If the image contains areas that should have a neutral color, then a gray eyedropper is used. To determine the black and white points, black and white pipettes are used, respectively. To use them, you need to select the desired pipette, just click it on the area that should be gray, black or white.

Pipettes can be used in conjunction with sliders in the dialog box Levels(Levels) or dots in the dialog box Curves(Curves). First, with the help of pipettes, the color shift is partially removed, and then a more subtle color and tone correction is carried out.

On fig. 7 shows an example of removing color shift using a white pipette. The click was made on the cloud located to the right of the dome of St. Isaac's Cathedral.

Rice. 7. Eliminate color shift and brighten the image with a white eyedropper (left - original image)

In addition to levels and curves, auto-correction can be performed using the command Image(Image) -> Automatic color correction(Auto Color). So, in fig. Figure 8 shows an example of image correction of the Kunstkamera building.

Rice. 8. Eliminate color shift using the Auto color correction command (left - original image)

When comparing the obtained result with Fig. Figure 2 shows that the result of auto-correction is closer to reality - it contains less blue color than in the case of using the dialog box Options(Variations). At the same time using the window Options(Variations), the water has taken on a bluish tint, making the picture look like a postcard. In any case, the choice is up to the user!

It should also be noted that the tool appeared in Photoshop CS5, which allows you to add liveliness and shine to a photo by increasing detail and glowing edges. This dialog box HDR toning(HDR Toning), which is in the menu Image(Image) -> Correction(Adjustments). In it, you can process the photo at the final stage of correction. So, in fig. 9 result obtained in the window Options(Variations), adjusted in the window Toning HDR(HDR toning).

Using the Dialog Box Hue/Saturation

Dialog window Hue/Saturation(Hue/Saturation) is not intended to balance the image by color. It applies to images that do not have a color shift! But it turns out to be indispensable for increasing or decreasing the saturation of the image, which is regulated by the corresponding slider (Fig. 10).

Moreover, this window allows you to influence certain colors of the image. So, in fig. 11 after a general increase in saturation, the sky was processed by affecting only the blue and blue colors. During the correction, brighter and more saturated colors of the image were obtained.

Rice. 11. The result of increasing the saturation of the image in the window Hue / Saturation (left - the original image)

Image Correction in Lab Mode

In the Lab color model, brightness is completely separated from the image, so to perform tone correction, it is enough to influence only
per luminance channel, and for color correction - per color channels a And b. Note that the Lab model has a wider color gamut than RGB, so you can seamlessly convert from RGB to Lab and back as many times as needed.

Tone correction in Lab mode

Before proceeding to the correction, you should convert the image to the Lab color model by executing the command Image(Image) -> Mode(Mode) -> Lab. On fig. 12 shows the image of the dome and its histogram, which shows that it is necessary to increase the contrast of the image.

Most tone correction tools are used to increase contrast, except for dialog boxes. exposition(Exposure) and HDR toning(HDR toning). On fig. 13 is an example of using the dialog box Levels(Levels), correction was made only in the channel Brightness(lightness). As you can see, now you need to increase the saturation of the image.

Saturate an Image in Lab Mode

To increase the saturation of a photo in the dialog box Curves(Curves) it is necessary to change the angle of inclination of the straight line in the channels a And b. On fig. 14 to increase the saturation of the photograph of the dome in both color channels, the angle of the straight line is increased by one value.

Rice. 14. The result of increasing saturation by increasing the angle of inclination of the straight line in both color channels of the Lab model

Please note that during the color correction in the Lab model there is much less noise than in the case of, for example, using the tool Hue/Saturation(Hue/Saturation) in the RGB model. So, in fig. 15 shows the result of increasing the saturation of a photograph of a landscape already familiar to us. The photo on the left is processed in the dialog box Hue/Saturation(Hue/Saturation) in the RGB model, which gave noise in the sky area. In this case, it was necessary to additionally process parts of the image with tools Blur(Blur) and Finger(Smudge) to remove multi-colored pixels (see Fig. 11). On fig. 15 (right) the same photo has been corrected only in the color channels of the Lab model in the window Curves(Curvers). As you can see, the correction did not create any noise.

In some cases, the Lab color model is useful for recoloring an image, as discussed in CompuArt #4'2011.

So, Photoshop provides quite a few tools for color and tone correction, the choice of which depends on the specific situation. It is better to carry out correction with several tools in order to choose the best result later.

The article was prepared based on the materials of the book “Photoshop CS5. The Essentials” by Sofia Skrylina