Adobe's implications for color correction and gray balance control
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Color correction is a very important part of image retouching. Color correction involves fine-tuning the tones, changing the contrast and color of the image.
Getting a good scanned image is a good start for all work. Although Photoshop can modify defective images, if the scanned image does not get enough color information, excessive color adjustment in Photoshop will result in more detail loss. So try to get high quality images when scanning, and the control before scanning is often important.
Before starting color correction, you can check the pixel values of the highlight and shadow of the image. Select the Info command in the Windosws menu to pop up the Info palette, move the mouse position on the image, and observe the brightest and darkest on the Info palette. Part of the pixel value, such as the brightest part of the RGB pixel value of 240, the darkest part of the RGB pixel value of 10, it means that the tonal range containing all of these pixel values has enough detail to obtain a rich layer of images.
The commands in the Image Adustments submenu are all commands for color adjustment. These commands modify the distribution of pixel values in the image and allow the tones to be adjusted within a certain accuracy range. Curve commands provide the most accurate adjustments. When performing a color gradation and curve command on individual channels of a color image to modify the color balance in the image, the curve command provides the most accurate control over the distribution of pixel values within the channel. The Hue/Saturatlon, Replace Color, and Selective Colol commands modify the specific colors in the image. The Varations command is often used to adjust the color that is too precise, which adjusts the color balance, contrast, and saturation of the image.
How to correctly reproduce the gray balance in the original during the scanning and copying process is a very important task, and it is a work that is difficult to do but cannot be done well. It is the basis for real-tone, hierarchical and color reproduction. The so-called color management system (CMS) is also based on achieving gray balance.
When color adjustment is performed on images in color scanning and Photoshop, the user usually only notices how to adjust the image displayed on the screen to make the whole picture closer to the original in terms of hue, brightness and contrast. However, it is often overlooked that a very important concept is that the images on the display are displayed in RGB mode. From the theoretical perspective of the three primary colors, neutral gray is produced in equal proportions of RGB, and the amount of mixing can be It presents various layers of light gray and dark gray.
There are two basic principles to understand when scanning:
(1) Highlights, midtones and shadows determine the hue of the image.
(2) Color combination can only be correctly implemented under the adjustment of gray balance, which is the basis of color existence.
(Note: Adobe explained the origin of gray balance, pointing out that "grey balance is derived from the color shift of printed four-color inks", but this does not mean that people working in the professional printing industry have reason to ignore this concept when correcting images. Sexual problem. Because the C, M, and Y three-color inks in the four-color printing cannot be overprinted into pure black, the neutral gray cannot be accurately reproduced, so a K version is added to compensate to make it more faithful to RGB. The true color of the gray-balanced original is reproduced. Therefore, the viewpoint that the neutral gray is only useful in printing is wrong. Professional color correction personnel must observe the RGB value and the CMYK color simultaneously when correcting the color cast of the image. Value, because anyone using the "color balance" command, in fact, is also in the manipulation of the complementary relationship between RGB and CMY, any professional color correction can not get rid of CMYK).
(1) Correction of color balance
Color balance refers to the adjustments that can be made in the color space. These adjustments can be done by curves and tone scales. Color balance is a change to individual colors, but changes can also indirectly affect other colors in the image. Color correction is for color balance, it only changes one color in the image without affecting other colors.
Image adjustments can be made for all colors or for a single channel. Using all the color adjustments often does not work well, because the image color cast is not all colors are color cast, most of them are one to two colors. With a single channel, you can adjust the color and seat level according to the specific conditions to achieve a satisfactory result.
Do not adjust the color in the fixed area. If the image has a color cast in a certain area or range, the image is color-shifted as a whole, and it is not the area that the visual sees. Correction of the image as a whole not only eliminates the noticeable color cast, but also adjusts the details that are not noticed.
Color shift means that the color of the image is different from the original color. When you see that a picture tends to a certain color, don't blindly remove the color. You should first consider the characteristics of the image used for the image. For example, landscape pictures are always biased towards cyan or yellow. When the color shift is used, a certain information can be highlighted or transmitted. Before removing the color shift, the position of the color shift should be clarified. The general color shift can be visually distinguished from the position. The color shift is mainly concentrated on the main color and reflection of the image. On the high light.
(2) Follow the following principles when correcting the color cast
(1) The color shift is not limited to only one color in the image.
(2) When an image appears to have a potential color shift, the bright portion should be checked first because the human eye is most sensitive to the color shift of the brighter portion.
(3) Neutral gray should be selected first when correcting the color shift, because neutral gray is an important means to compensate for the color shift. When correcting gray in the color part, don't believe the color that the human eye presents. It is true that other colors in the image will change the human eye's feeling of gray. This is what we call the influence of the ambient color. The pipette tool is checked.
(4) When correcting the color shift, try to adjust the complementary color of the color.
(5) According to the specific requirements of the image, the HLS mode can be used for adjustment.
(6) The color shift of many images is quite severe in some tonal ranges. If you only adjust this part of the color tone, the color tone other than the adjustment will be changed sharply, so it is necessary to coordinate the entire tonal range.
(3) Several typical color casts
(1) The original that is raining on a cloudy day looks like it is covered by a layer of light blue. Because there is no sunlight on a cloudy day, it lacks red.
(2) The positive film taken by the fluorescent lamp as the light source sometimes produces a greenish phenomenon. This is because the light emitted by the fluorescent lamp appears to be self-colored, but in fact, the white color contains a strong color, if a color negative film is used. Direct shooting must result in a color shift.
(3) The color shift caused by the film itself is different due to the date of manufacture of the manufacturer's mouth, so the tendency of the film to have color is also different. This color shift is a small amount of color shift and does not cause color shift as a whole.
(4) Most of the originals have colors in memory, such as the familiar sky, various trees, flowers and flowers, etc. If these colors change, the human eye will be easy to find.
(5) Fine color shift is a color shift that is not noticed by the human eye. The solution to these color shifts is to look for neutral gray in the image or color in memory as a standard.