Several color modes of digital images (four)

(4) Special color modes provided by Photoshop

Bitmap mode

Two color values ​​(black and white) are used to represent the pattern of pixels in the image. The bitmap mode image is also called a black and white image, or a bitmap because its bit depth is 1.

2, gray mode

Each pixel of a grayscale image has a luminance value between 0 (black) and 255 (white) for a total of 256 gray levels. The gray value can also be expressed as a percentage of black ink coverage (0% equals white and 100% equals black). Images produced using black and white or grayscale scanners are often displayed in "grayscale" mode. Bitmap mode and color image can be converted to grayscale mode.

To convert a color image to a high-quality black and white image, Photoshop throws away all the color information in the original image. The gray level of the converted pixel represents the brightness of the original pixel.

You can use the Channel Mixer command to mix color channel information to create a custom grayscale channel.

When converting from grayscale to RGB, the pixel's color value is based on the previous grayscale value. Grayscale images can also be converted to CMYK images (for creating four-tone printing colors without having to convert to "two-tone" mode) or Lab color images.

3, dual tone mode

Create two-tone (two-color), three-tone (three-color), and four-tone (four-color) grayscale images using two to four color inks. Photoshop allows the creation of single-tone, two-tone, three-tone, and four-tone images. Monotone is a grayscale image printed with a single, non-black ink. Two-tone, three-tone, and four-tone are grayscale images printed with two, three, and four inks. In these types of images, color inks are used to reproduce light gray shades rather than reproduce different colors.

The term "duplex" in this section refers to duotone, monotone, tritone, and tetratone.

4, the index color mode

Use up to 256 colors. When converting to an indexed color, Photoshop builds a color lookup table (CLUT) that stores and indexes the colors in the image. If a color in the original image does not appear in the look-up table, the program will select the closest color in the existing color or use the existing color to simulate the color.

By limiting the color palette, index colors can reduce file size while maintaining visual quality. For example, for multimedia animations or web pages. Only limited editing is available in this mode. If you want to edit further, you should temporarily convert to RGB mode.

5, multi-channel mode

Use 256 gray levels in each channel. Multi-channel images are very useful for special printing. For example, converting duotones for printing in the Scitex CT format

The following guidelines apply to converting images to "multi-channel" mode

· Any image synthesized by more than one channel can be converted to a multi-channel image, and the original channel is converted to a spot color channel.

• When converting a color image to multiple channels, the new grayscale information is based on the color values ​​of the pixels in each channel.

· Converting CMYK images to multiple channels creates cyan, magenta, yellow, and black spot channels.

· Convert RGB images to multiple channels to create cyan, magenta, and yellow spot channels.

• Deleting a channel from an RGB, CMYK, or Lab image automatically converts the image to multi-channel mode.

It is often not possible to print color composite images in "multi-channel" mode, and most output file formats do not support multi-channel mode images, but can output such files in Photoshop DCS 2.0 format.

School color: the difference between RGB and CMYK

Advances in color management, digital photography, and color scanning have prompted new and old scanner operators to carefully consider when to perform color corrections and when to perform color separations. Drum scanner operators use conventional methods to generate scanned images consisting of yellow, magenta, cyan, and black, but today's new tools lead to the widespread adoption of new workflows—that is, scanning before separation into CMYK. School color. This article explains the advantages of this method as well as some background knowledge about scanning, color correction, and color separation.

Both scanning and digital photography capture red, green, and blue information about the image, but various methods of image capture generate different amounts of information depending on their depth.

Although most scanners use 1 byte (8 bits) of information in each color channel, it has become increasingly common for scanners and digital cameras to use more than 8-bit bytes to describe each basic color. These additional bits are used to capture a large number of dark shades for each pixel, producing a subtle description (mostly grey tone) between the multicolor and the maximum color of each channel. The number of bits used for each channel is what we call the bit depth of the digital image.

For example, in an RGB mode with an 8-bit depth per channel, a total of 24 bits are used for scanning or digital photographs to describe the color of each pixel, which is called 24-bit color, since 8 bits per channel count, 3 The channel (red, green, blue) is a total of 24 bits per pixel location. Other common configurations for capturing RGB data include:

10 bits per channel (also known as 30-bit color because there are 3 channels in 10 digits);

12 bits per channel (36-bit color);

16-bit per channel (48-bit color).