Color models, spaces, and modes in Photoshop

If you want to be an expert in image editing then you must be knowledge about colors and color modes. Pictures are a collection of pixels and each pixel is filled with a single color.If you want to work effectively with photoshop then you must know the color basics. How colors are made? and how they changes?

In digital world there are three Pure colors of light red, green, and blue that produce all the colors in the visible spectrum. This colors are called Additive Primaries.
In the other hand there are four pigment colors of light (cyan, magenta, yellow, and black) called Subtractive primaries.

A color model describes the colors we see and work with in digital images. Each color model, such as RGB, CMYK, or HSB, represents a different method (usually numeric) for describing color.

A color space is a variant of a color model and has a specific gamut (range) of colors. For example, within the RGB color model are a number of color spaces: Adobe RGB, sRGB, ProPhoto RGB, and so on.
Each device, like your monitor or printer, has its own color space and can only reproduce colors in its gamut(range). That’s why when an image moves from one device to another, image color changes.

Photoshop CS3 has 8 Color modes. Those are:

  1. RGB Color mode
  2. CMYK Color mode
  3. Lab Color mode
  4. Grayscale mode
  5. Bitmap mode
  6. Duotone mode
  7. Indexed Color mode
  8. Multichannel mode
  1. RGB color mode is one of the most use color mode worldwide. RGB stands for Red, Green and Blue. In RGB mode images use three colors, or channels, to reproduce colors on-screen. In this mode a 8-bits-per-channel images can have a pixel that has a R value of 231, G value of 54 and B value of 156, this values can be anywhere between 0-225.
    When the values of all three components are equal, the result is a shade of neutral gray. When the values of all components are 255, the result is pure white; when the values are 0, pure black.
    In RGB mode a 24?bit(8 bits x 3 channels) image can reproduce up to 16.7 million colors per pixel, and even much more for higher bit images.
  2. CMYK color mode In the CMYK mode, each pixel is assigned a percentage value for each of the process inks. The lightest (highlight) colors are assigned small percentages of process ink colors; the darker (shadow) colors higher percentages. For example, a bright red might contain 2% cyan, 93% magenta, 90% yellow, and 0% black. In CMYK images, pure white is generated when all four components have values of 0%.
    Use the CMYK mode when preparing an image to be printed using process colors. Converting an RGB image into CMYK creates a color separation. If you start with an RGB image, its best to edit first in RGB and then convert to CMYK at the end of your process. In RGB mode, you can use the Proof Setup commands to simulate the effects of a CMYK conversion without changing the actual image data. You can also use CMYK mode to work directly with CMYK images scanned or imported from high-end systems.
    Although CMYK is a standard color model, the exact range of colors represented can vary, depending on the press and printing conditions. The CMYK Color mode in Photoshop varies according to the working space setting that you specify in the Color Settings dialog box.
  3. Lab Color mode The CIE L*a*b* color model (Lab) is based on the human perception of color. The numeric values in Lab describe all the colors that a person with normal vision sees. Because Lab describes how a color looks rather than how much of a particular colorant is needed for a device (such as a monitor, desktop printer, or digital camera) to produce colors, Lab is considered to be a device-independent color model. Color management systems use Lab as a color reference to predictably transform a color from one color space to another color space.
    The Lab Color mode has a lightness component (L) that can range from 0 to 100. In the Adobe Color Picker and Color palette, the a component (green-red axis) and the b component (blue-yellow axis) can range from +127 to 128.
    Lab images can be saved in Photoshop, Photoshop EPS, Large Document Format (PSB), Photoshop PDF, Photoshop Raw, TIFF, Photoshop DCS 1.0, or Photoshop DCS 2.0 formats. You can save 48?bit (16?bits-per-channel) Lab images in Photoshop, Large Document Format (PSB), Photoshop PDF, Photoshop Raw, or TIFF formats.
  4. Grayscale mode uses different shades of gray in an image. In 8?bit images, there can be up to 256 shades of gray. Every pixel of a grayscale image has a brightness value ranging from 0 (black) to 255 (white). In 16 and 32?bit images, the number of shades in an image is much greater than in 8?bit images.
    Grayscale values can also be measured as percentages of black ink coverage (0% is equal to white, 100% to black).
    Grayscale mode uses the range defined by the working space setting that you specify in the Color Settings dialog box.
  5. Bitmap mode uses one of two color values (black or white) to represent the pixels in an image. Images in Bitmap mode are called bitmapped 1?bit images because they have a bit depth of 1.
  6. Duotone mode creates monotone, duotone (two-color), tritone (three-color), and quadtone (four-color) grayscale images using one to four custom inks.
  7. Indexed Color mode produces 8?bit image files with up to 256 colors. When converting to indexed color, Photoshop builds a color lookup table (CLUT), which stores and indexes the colors in the image. If a color in the original image does not appear in the table, the program chooses the closest one or uses dithering to simulate the color using available colors.
    Although its palette of colors is limited, indexed color can reduce file size yet maintain the visual quality needed for multimedia presentations, web pages, and the like. Limited editing is available in this mode. For extensive editing, you should convert temporarily to RGB mode. Indexed color files can be saved in Photoshop, BMP, DICOM, GIF, Photoshop EPS, Large Document Format (PSB), PCX, Photoshop PDF, Photoshop Raw, Photoshop 2.0, PICT, PNG, Targa, or TIFF formats.
  8. Multichannel mode images contain 256 levels of gray in each channel and are useful for specialized printing. Multichannel mode images can be saved in Photoshop, Large Document Format (PSB), Photoshop 2.0, Photoshop Raw, or Photoshop DCS 2.0 formats.

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