Thursday, December 15, 2011

Digital image quality

When we talk about the quality of a digital image we usually are thinking of two things:
• the total number of pixels that compose the image
• the number and accuracy of the colors in the image

The number of pixels is expressed in two ways:
• the dimensions. For example, an image might be said to be 1024 x 768 pixels
• the total number pixels in the image. For example, an image might be said to be a 1.5 megapixel image.

An image file with more pixels will produce a higher quality image and will make larger prints better than an image with fewer pixels.

The second quality measure is the total number of colors recorded in the image file. We call this the bit depth of the image. It's the number of colors possible in a digital file.

Sometimes the number of colors is referred to as bits per color channel. Most image files have three channels - red, green and blue. This results in three times the bits per channel.

• 8 bits per color channel or 24-bit total color = 16.7 million colors
• 8-bit color = 256 colors
• 4-bit color = 16 colors
• 1-bit color = 2 colors