Understanding Color Modes in Photoshop

RGB, CMYK, Indexed Color, Greyscale, they all serve a purpose and they all serve them well. In this article I'll try breakdown the difference between the most common colour options and their uses in Photoshop and other applications.

Bitmap - A bitmap image is made up of black or white and nothing in between. A bitmap image is best used for line drawings, signatures, or logos made up of one solid colour. If the resolution of a bitmap image is high enough, a bitmap image will print great, but often doesn't look too sharp on the web.

Greyscale - Think black and white photo here. A greyscale image has black, white, and every scale of grey in between (256 of them actually). Images in greyscale are used in printing, one color will print the entire image, most often a black ink, and the shades of grey are just less heavy ink (called halftones). On the web, greyscale images are generally saved a .jpg files and are a smaller image file for downloading then saved in a colour format.

Duotone - An image in duotone color mode is quite simply an image with 2 ink color mixed to create a colored effect. This is quite handy when running a print job on a two color press. You choose the two colors to blend, say a black and a red, and photoshop blends the two colors over your image to give you a nice effect (much like a sepia tone but with greater control). A monotone is quite simply one ink and a tritone and quadtone use a mix of three and four colors respectively.

Indexed - A file using Indexed color mode can handle only a specific, user defined color palette, usually used for files to be emailed or on a website. You can use a colour range of up to 256 colours to define your image making it a smaller file size, however the quality of your image is severely compensated. A poor choice if you want to print your file, but if it still looks good on the screen it is a good choice for the web.

RGB - Red, Green, and Blue. The same color system that makes up viewing an image on a computer monitor (also the same as on a tv). The process of defining your image is to blend the three main colors (Red, Green, and Blue) to achieve the desired color in your fil. It's the image color of choice for photos viewed on screen. It has the widest range of color available for your photoshop image.

CMYK - Cyan, Magenta, Yellow, Black. This process takes the aforementioned four colors and blends them to achieve the desired color of your image. This process is the same as on a full color printing press, therefore if you are printing your image file, this color mode gives you the most accurate representation of what will be printed. Remember however your monitor is RGB so your CMYK color mode won't view perfectly on your monitor compared to a printed sheet.

Hope that helps some.