Lossy vs. Lossless

As we keep saying, bitmapped images are made simply of zeros and ones. In an 8-bit grayscale image, each pixel is defined by eight zeros or ones. If images are already reduced to this level of simplicity, how can they be reduced further? By bundling groups of bits together into discrete chunks.

Lossless Compression

Let's take the example of a 1-bit (black-and-white) bitmap, 100 pixels wide and tall. Without any compression, the computer stores the value (zero or one) for each one of the 10,000 pixels in the image. This is like staring into your sock drawer and saying, “I've got one blue sock and one blue sock and one black sock and one black sock,” and so on. We can compress our description in half by saying “I've got one blue pair and one black pair.”