Image compression possibilities

<p>I would like to know if anybody has any experience with image compression using Go.</p> <p>I have to create multiple smaller versions of many images (mostly jpg, some png), which works really great using Go.</p> <p>But well, the customer found Google Page Speed Insights, which tells him that images could be smaller by X % with compression blablabla...</p> <p>Any ideas how I could shrink filesizes with native Go? I&#39;m not a friend of using jpegoptim with cli calls, couldn&#39;t find a Go port and tbh my math-fu isn&#39;t good enough to understand and implement the used algorythms myself :( </p> <p>Also, what do you think about stripping EXIF and similar unncessary things that photoshop/lightroom/etc add to files?</p> <hr/>**评论：**<br/><br/>kjell_k: <pre><p>Hi.</p> <p>In image/jpeg.Encode - you have a quality option - you can lower this a bit to reduce file size and stil have good quality.</p> <p><a href="https://golang.org/pkg/image/jpeg/#Encode" rel="nofollow">https://golang.org/pkg/image/jpeg/#Encode</a></p> <p>Sorry for brief reply. Just have my Phone here :)</p></pre>joetsai: <pre><p>The PNG package in the standard library uses compress/flate under the hood. The algorithm in flate has been vastly improved over the years, but the compression ratio still falls short slightly when aiming for highly compressed static content.</p> <p>There are several reasons:</p> <ul> <li>For performance reasons, compress/flate only performs 4-byte offset matches, while the DEFLATE format actually allows for 3-byte matches. This sometimes matters for images without an alpha channel (RGB is 3-bytes).</li> <li>Most PNG crushers use a specialized implementation of DEFLATE that heavily sacrifice compression speed for compression ratio (see <a href="https://en.wikipedia.org/wiki/Zopfli" rel="nofollow">https://en.wikipedia.org/wiki/Zopfli</a>). This algorithm does not exist in compress/flate.</li> <li>(not specific to compress/flate) Some PNG crusher are actually lossy in that they discard some details from the image that humans cannot perceive so that DEFLATE can further benefit from more matches.</li> </ul> <p>I can&#39;t really speak for JPEG and other lossy formats.</p></pre>WikiTextBot: <pre><p><strong>Zopfli</strong></p> <p>Zopfli is data compression software that encodes data into DEFLATE, gzip and zlib formats. It achieves higher compression than other DEFLATE/zlib implementations, but takes much longer to perform the compression. It was first released in February 2013 by Google as a free software programming library under the Apache License, Version 2.0. The name Zöpfli is the Swiss German diminutive of “Zopf”, a unsweetened type of Hefezopf.</p> <hr/> <p>^[ <a href="https://www.reddit.com/message/compose?to=kittens_from_space" rel="nofollow">^PM</a> ^| <a href="https://reddit.com/message/compose?to=WikiTextBot&amp;message=Excludeme&amp;subject=Excludeme" rel="nofollow">^Exclude ^me</a> ^| <a href="https://np.reddit.com/r/golang/about/banned" rel="nofollow">^Exclude ^from ^subreddit</a> ^| <a href="https://np.reddit.com/r/WikiTextBot/wiki/index" rel="nofollow">^FAQ ^/ ^Information</a> ^| <a href="https://github.com/kittenswolf/WikiTextBot" rel="nofollow">^Source</a> ^] ^Downvote ^to ^remove ^| ^v0.27</p></pre>peterhellberg: <pre><p>You can try this package if you want to experiment with lossy PNG compression: <a href="https://github.com/peterhellberg/lossypng" rel="nofollow">https://github.com/peterhellberg/lossypng</a></p> <p>For JPEG you can use the quality option in the syandard library to reduce the file size (and visual quality)</p> <p>Let me know if you find any (Go) native implementations of JPEG optimizers.</p></pre>SSoreil: <pre><p>On stripping EXIF, it&#39;s highly unlikely to be a significant amount of data. Files which do have a lot of EXIF data are probably straight out of camera and aren&#39;t what you are putting up to begin with. Also, stripping out EXIF data for no reason might not be what you want at all points.</p> <p>Not that I know much about the rather arbitrary goal you are trying to reach here, if you want to crush files you probably want to call out to the CLI for that. I wrote some binding for PNGquant or whatever it&#39;s called a few years back to call it as a library and it was very inconvenient. I don&#39;t think the code still exists at this point.</p> <p>image/jpeg and image/png are probably good enough.</p></pre>