Photoshop color mode complete manual (2)

Fifth, other color modes

In addition to the basic RGB mode, CMYK mode, and Lab mode, Photoshop supports (or processes) other color modes including bitmap mode, grayscale mode, dual tone mode, index color mode, and multichannel mode. And these color modes have their special use. For example, an image in a grayscale mode has only a grayscale value and no color information; although an indexed color mode can use a color, there are very few colors that can be used with respect to the RGB mode and the CMYK mode. Here are some of these color modes.

Bitmap mode

Bitmap mode uses two colors (black and white) to represent the pixels in the image. Bitmap mode images are also called black and white images. Because its depth is 1, it is also called a bit image. Because bitmap mode only uses black and white to represent the pixels of the image, it loses a lot of detail when converting the image to bitmap mode, so Photoshop offers several algorithms to simulate the missing details in the image.
In the case of the same width, height, and resolution, the bitmap mode image size is the smallest, about 1/7 of the grayscale mode and less than 1/32 of the RGB mode.

2. Grayscale mode

Grayscale mode can use up to 256 levels of grayscale to represent the image, making the transition of the image more smooth and delicate. Each pixel of the grayscale image has a luminance value between 0 (black) and 255 (white). The gray value can also be expressed as a percentage of black ink coverage (0% equals white, 100% equals black). Images produced using black-fold or grayscale scanners are often displayed in grayscale.

3. Duotone mode

The two-tone mode uses 2-4 color inks to create an image composed of two colors (two colors), three colors (three colors), and four colors (four colors) mixed with their color gradations. In the process of converting a grayscale image to a dual tone mode, the tone can be edited to produce a special effect. The main purpose of using the dual tone mode is to represent as many color levels as possible with as little color as possible, which is important for reducing the printing cost, because at the time of printing, each additional tone requires a greater cost.

4. Indexed Color mode

The index color mode is an image mode commonly used in online and animation, and includes 256 colors when a color image is converted to an index color image. The index color image contains a color table. If the colors in the original image cannot be represented by 256 colors, Photoshop will select the closest colors from the available colors to simulate these colors, which can reduce the size of the image file. It is used to store the colors in the image and create color indexes for these colors. The color table can be defined during conversion or modified after alleging indexing.

5. Multichannel mode

Multi-channel mode is useful for images that have special printing requirements. For example, if only one or two or three colors are used in the image, using multi-channel mode can reduce the printing cost and ensure the correct output of the image color.

6. 8-bit/16-bit channel mode

In grayscale RGB or CMYK mode, 16-bit channels can be used instead of the default 8-bit channels. According to the default situation, the 8-bit channel contains 256 color gradations. If it is increased to 16 bits, the number of gamuts per channel is 65536, which can get more color details. Photoshop can recognize and input images of 16-bit channels, but for this kind of image, there are many restrictions, all filters cannot be used, and 16-channel mode images cannot be printed.

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