20.3. When to Use JPEGs
As mentioned earlier, JPEGs, with their 24-bit color capacity and specialized compression scheme are ideal for photographic and other continuous-tone images, such as paintings, watercolor illustrations, and grayscale images with the 256 shades of gray (see Figure 20-1).
Figure 20-1. Examples of images appropriate for JPEG format
JPEGs are notably not good at compressing graphical images with areas of solid color, such as logos, line art, type, and cartoon-like illustrations. JPEG's lossy compression makes flat colors blotchy and pixelated, resulting in unacceptable loss of quality in some cases. Not only that, the files are generally quite a bit larger than a GIF file of the same image. JPEG compression is also not good at sharp edges or typography since it tends to leave artifacts that "ripple" the edges.
It is usually best to let JPEGs handle photographic material and leave the flat graphics (including graphics containing text) to GIF.
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