Different Color Modes in PhotoShop

 You need to be aware of two color models as you start working with Adobe Photoshop.  These are the RGB (Red, Green, and Blue) and CMYK (Cyan, Magenta, Yellow and Black) color models.

RGB is important because it mirrors the way the human eye perceives color. It is the model used by scanners and digital cameras to capture color information in digital format and it is the way your computer monitor describes color.

Note Well:

The R.G.B mode is also referred to as the true color mode

Red green and blue are referred to as “additive primaries”

You can add varied proportions of the three colors to produce millions of

Different colors(R   G   B).

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If you add 100% of red green and blue light together you will get the white.

You produce the “secondary” colors, when you add red and blue to get magenta; Green and blue to get cyan; red and green to get yellow.

The CMYK color model is referred to as the “subtractive” color model.

C  M Y K

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It is important because it is used by the printing presses.

If you subtract cyan, magenta and yellow when printing you end up with the complete absence of color - white.

If you add all cyan magenta and yellow when you print you get black.

The shade in CMYK is of lighter intensity.

Grayscale Mode

Grayscale mode images use 8 bits of color information per pixel. The number of 1’s and 0’s arrangement provides 256 range of colors.

Each of these values can be assigned a gray tonal value ranging from white to black, however a grayscale image is not a black and white image.

Note well: Generally the file size for a grayscale can be 1/3 of that of an RGB.

Additionally, the computer should work much faster in a gray scale mode.

Bitmap mode image

An image converted to bitmap mode is really a black and white image. It contains one bit of color information per pixel.

2^1 = 2 colors

Fax machines uses bitmap mode

Index mode

The index mode is limited to the maximum of 256 colors and is useful when preparing images for viewing on the monitor. It is a technique for managing colors in a limited fashion in order to save computer memory and file storage thus speeding up display, refreshing of your monitor and also for the fast loading of web pages.

Multichannel mode

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.

These guidelines apply when converting images to Multichannel mode:

 Layers are unsupported and therefore flattened.

 Color channels in the original image become spot color channels in the converted image.

 Converting a CMYK image to Multichannel mode creates cyan, magenta, yellow, and black spot

channels 

 Converting an RGB image to Multichannel mode creates cyan, magenta, and yellow spot channels.

 Deleting a channel from an RGB, CMYK, or Lab image automatically converts the image to Multichannel mode, flattening layers.

 To export a multichannel image, save it in Photoshop DCS 2.0 format.

Reference: Photoshop help / color modes (N.D.) retrieved from   https://helpx.adobe.com/photoshop/using/color-modes.html