I understand that graphic images do not compress well when using a lossless compression archive file format like .zip. Is there an image file type that losslessly compresses better (smaller) than the others?
2 Answers
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Which image file format compresses the most when using a lossless data compression archive file format (like .zip)?
Lossless image compression algorithms implemented in image file format use the same methods as general purpose compression software, plus some specific methods based on image models. These methods tend to remove data redundancy and to provide a variable length coding that exploits data statistics to reduce coding cost.
Hence if a compressed image can be significantly recompressed by, say, zip, it is probably not a very efficient file format in terms of compression. So to answer your question, the image file format that can be the most efficiently compressed by zip is the format with the least internal compression. And the final result will be worse than using a good lossless image compression method and skipping the zip recompression.
There are good lossless image compression methods available. The compression ratio is of course worse than the one provided by lossy compression, but can be decent, depending on your need. In standard methods, you can use png of lossless jpeg2000. And the are very good non standard methods, as webP, FLIF or BPG. But with none of them you will have any significant gain if using zip on these images.
