Slicing and Saving Graphics in Photoshop for Use on the Web - Functional Formats
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Save for web is, in my opinion, one of the coolest tools in Photoshop. It lets you index the colors, show final file sizes, set compression options, and even show approximate load times for your image. There are basically four formats you can choose from for saving your files: JPEG, GIF, PNG 24, and PNG 8.
JPEG
JPEG is probably the most commonly used and most widely supported image format you’ll ever find. However it’s not always the best to use. The JPEG format supports 24-bit color, so JPEG graphics can have up to 16 million colors. This allows JPEG graphics to preserve subtle variations in color and smooth gradients, however, the JPEG compression method can degrade sharp detail in images containing type, line art, logos, or vector art. JPEG is a lossy compression technique, which means that it compresses by selectively discarding data so it can make file sizes smaller to about 6% of the images normal size; however, some details can be lost. JPEG’s compression still isn’t very sufficient for web use because while it has great compression, it still has a slightly high file size.
GIF
GIF is a great image format, which was actually developed for the web. It is an 8-bit color format, which means that it can save up to 256 different colors. The GIF format compresses large areas of solid color while preserving detailed areas. GIF is a lossless compression up to 256 colors, and it also supports background transparency, animations, and matting. GIF compression produces great file sizes, but, due to the 256 color limitation images usually look horrible and slightly “blotchy”.
PNG
PNG is a newer image format was produced to replace GIF because of the patent by CompuServe on GIF’s compression. This means that software developers that use it have to pay a royalty. PNG however is free for everyone. PNG has two types of compression, PNG-8 and PNG-24. PNG-8 is more like the GIF format. It supports 256 colors and is usually 15% to 40% smaller than GIF, even for the same image. It’s also a lossless compression which means no image data is lost when saving. PNG-24 is more comparable to JPEG. As the name suggests it's a 24-bit compression which supports 16 million colors, and when compared to JPEG it’s usually 10% to 30% smaller than the JPEG equivalent. Both PNG types support Multi-Level background transparency.
Now that you understand the difference in the image formats you can use, I always use PNG-8 as it’s shown to have the best quality and file size for web usage. In the save for web tool, the best idea is to show the “4-Up” tab and compare all the different formats for your image. Then after you’ve found the format you want to use, use the “4-Up” tab again to compare four different settings for your image. I’ve found that for all my slices on my layout, I like to use PNG-8 with 128 colors, 88% dither, and 0% web snap. Those are actually my usual settings for all my images because it produces very smooth gradients while file size stays very small. Now let me explain the settings that you set on the save dialog that pops up when your done with the “Save for web” tool.
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