A major part of digital image manipulation involves combining images. To do this effectively, you need to explore the concepts of color modes and resolution.
Using two (or more) images together requires a little more preparation, and, in particular, needs both images to be compatible. In this context ‘compatible’ means that both images should be of similar resolution – that is, that the pixel dimensions of each are either similar or can be made similar – and that each image is of the same image mode. In conventional photography you have two principal image modes: black and white, and color. In digital photography, you have more. Here’s a summary of the principal modes and their uses.
The digital equivalent of conventional black and white is the Greyscale mode. Greyscale images contain all shades of grey, along with black and white.
In Bitmap mode, the image is reduced to (just) black and white tones. When a greyscale image is converted to bitmap, greys lighten, median values become white, and those darker become black.
The Duotone mode is somewhat anomalous – a monochrome image to which an additional color has been added. This can produce potent images when used effectively, though it tends to be used mostly in the printing world to introduce a little color into otherwise monochrome images. Tritone and Quadtone modes are similar, but with two and three added colors respectively.
RGB (red, green, blue) mode is a popular full-color mode, used to represent color images on computer monitors. CMYK (cyan, magenta, yellow, black) mode is a similar full-color mode that is used for images intended for print (cyan, magenta, yellow and black are the colors of the inks used in color printing). There are minor differences (due to the practical methods of representation) between CMYK and RGB color modes.
You might, exceptionally, encounter alternate color modes such as Lab Color or Indexed Color. These tend to have specialized uses. Virtually most of the images were created in RGB mode prior to conversion to CMYK at the printing stage.
Image modes tip
Experimenting with image modes can cause irreversible changes to your treasured photos. Make a copy of the image first, then perform the changes. When you convert an image to greyscale, the color information is discarded and can’t normally be retrieved.
