The principle of the detailed example of Photoshop to resolve the calculation command

This tutorial mainly uses the Photoshop detailed example to parse the calculation command principle, through the channel uses the computation command to calculate the exact selection, applies the image command to adjust the color. Different from hue/saturation, color balance color adjustment mode.

Blending mode is the soul of the Computing command, using the calculation command for the selection

Many people often ask: what is the essence of the calculation order?

The Photoshop Help file describes the calculation command, which allows you to mix two individual channels from one or more source images. You can then apply the results to a new image or new channel, or to a selection of active images. You cannot apply a calculation command to a composite channel.

It is a description of the computational process, which is crystal clear to readers who can skillfully use computing commands, but it is too abstract for beginners of computing commands.

May I ask the above question to say, the calculation order can do for us? If it's just flashy image changes, then this command is not worth the attention of Photoshop users.

The greatest value of a command is that it provides a powerful and precise way to choose. This approach is different from the traditional selection method (such as lasso) used by beginners in the toolbox. It takes the pixel's own attributes (such as brightness, hue, saturation, etc.) as the starting point, through a series of determined ways to determine the choice of pixels, and this trade-off in the form of channel images, and ultimately in the form of choice, For the user's image processing services.

So, do not think that the dazzling image change of the command is just for the special effect (it has the purpose), its main purpose is to make the image as the choice, and with the help of the choice, so that the user can accurately change the image.

The calculation command is an additive plant whose raw material is a variety of selections (selections, masks, channels), and the product is a new channel (document, selection). And the blending mode is the production line.

The same raw materials are sent to different production lines to produce different products.

So open the Calculation Command dialog box, the user becomes a factory director. What you want to do, the first choice is to decide what products to produce, then purchase the appropriate raw materials, determine what kind of production process, and send raw materials to the production line.

Tip: In the process of exploring computing commands, many people are often caught in the middle of three dilemmas: they don't know what products they need (choose), don't know much about the characteristics of the raw materials (what kind of channels they choose), and they have no idea about the production process (mix). In this case, to get the satisfactory result, I am afraid only by luck.

Of all the elements, the most important is the blending mode, which is the soul of the Computing command. Mixed mode is such a wonderful thing: before it is not understood its essence, it is a dose of ecstasy, but once mastered the law, it is a sharp sword. For the user to choose the way to hack.

Darken and lighten

Dimming and brightening patterns are a couple that are often accompanied in the calculation commands to isolate certain brightness features. Both of these modes are particularly useful in lab mode because the lab channel has two color channels.

Tips:

In lab mode, the color channel is a, b, and in the histogram, red and green occupy the bright and dark areas of a channel respectively, and yellow and blue occupy the bright and dark areas of B channel respectively. Depending on the brightness and dimming mode, combined with 50% gray channels, can be easily divided into 4 kinds of colors.

As shown in Figure 5.56 is a picture of a tulip, where red, green and yellow are the main colors of the picture. If you use the Hue slider of the general Hue/saturation command to adjust the green to make the leaves greener, you will find that the green adjustment is not synchronized, and the area of green saturation remains unchanged when the green-saturated area of the original image is blue. This is a performance of Matthew effect in image processing.

In fact, the part of the grassland in the picture is not so much green as the yellow component is larger. However the adjustment of yellow will inevitably affect the yellow of the tulip flowers. Although some users who are proficient with hue/saturation commands use a straw to carefully exclude these yellows, there are still too many human factors in this operation. The reader can turn on the hue/saturation command, and drag the Hue slider in green and yellow separations to experience the pros and cons of this conventional adjustment method.

A more efficient approach is to change the A and B color channels in lab mode, especially for images that are red and green in contrast. In general, landscape images are more suitable for processing in lab mode.

The first step: Use the image → mode menu to convert the image mode from RGB to lab mode.

Step two: Do not rush to the next operation, in the image processing, observation is sometimes more important operation.

Lab mode is a color pattern we do not use, and it is essential to observe its various channels, especially the color channel, because the channel image of A, B color channel that only represents color distribution is as illegible as that of the Yumingdo channel, which is consistent with people's visual habits.

There are two colours in a channel, red and green. With 50% as the boundary, the channel image is greater than 50% gray area (darkened) is green, the darker the area, the greater the saturation of green, the more the channel image is less than 50% gray area (high light) is red, the brighter the area, the greater the saturation of the red.

Because the red tulip is very bright on the image, the reader can distinguish the brighter flower shape from the A channel image.

For b channel, because this example does not need to adjust, did not post the diagram and analysis, but suggested that the reader also take a look at the B channel, deepen the blue-yellow channel of the intuitive impression.

Step three: Create a new channel and fill it with 50% Gray using the Fill command in the Edit menu.

Tips:

This is an obscure operation, but it is the core step in this example. This 50% gray layer is like a sieve that filters out one color and retains another.

Fourth step: Use the calculation command, preferred to explicitly use this command to do something.

In this case, we want to individually adjust the green without affecting the other colors, then we need a channel based selection, in which only green, no red. In channel A, this means that all areas that are brighter than 50% Gray are turned to 50% Gray.

Next, we will use the calculation command to achieve this goal.

The two source channels are set to Alphal and a respectively (depending on the nature of the dimming and dimming modes, the two channels who first have no difference), and the blending mode is dimmed.

The Alphal channel, like a machete, cuts the high light portion of a channel, and the reader can see from the computed Alphal 2 channel image that the tulip flower turns 50% gray.

Fifth step: With the Alphal 2 channel, we can make a transformation of the Alphal channel, so that the image of green greener.

First click on a channel, rendering will be a channel grayscale image. Click the eye icon in front of the AAB compound channel to make it visible so that we can observe the changes in the color image while editing a single channel.

Sixth step: Use the image command for a channel, set as shown in the following figure, the channel is Alphal 2, the blending mode is superimposed.

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• PS Getting Started Tutorial