Compression Info (Formerly: Tips on Keeping Your Entry under 75kb in size.)

[ravells]

Please post any tips on keeping low file sizes here.

One of the parameters in this month's competition is to keep entry file sizes under 75kb but with a resolution of at least 1280 x 1024 pixels in either jpg or png formats.

As our community are used to producing maps in the low megabyte file size range, this parameter is likely to present one of the most formidable challenges in the competition if, like me, you do not know much about file compression and the pros and cons of jpg v png.

If you are a file compression master, then please post your explanations and tips here for those of us who are technically less adept.

Redrobes and gameprinter have already given some invaluable advice as follows:


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• Solid blocks of color and PNG would probably win. The very worst thing for all images is random noise followed by thin lines ! If you have a door in an old school map then its better being solid rect than an open box for example. Also, lines that are horizontal and vertical will be much better than ones at an angle. With JPG its a bit more complicated knowing what shapes would compress better as all the compression isl done in frequency space. JPG will have about 16K minimum size even if its all white but PNG would be a few hundred bytes. Also, ensure you save your PNG with specific number of colors 1, 16, or full. If you have < 16 colors then don't save full color as its hugely more expensive.
• no anti-alias, minimal colors, etc, is completely unnecessary to still create a map that falls under 75 KB and at 1280 x 1024 pixel JPG. The difference is maximum compression JPG file and the best compression method.
• The antialiasing is only going to make minimal difference. With PNG it would add a little but with JPG anti aliasiing would likely drop the size a little !