![]() ![]() I distinctly remember that Mandrill image from my Amiga days. * An entire set of classic reference images is available from the USC-SIPI image database. ![]() There's virtually no effect at all on file size, which stays constant at 30-31 kilobytes even through generation 15. By generation five, you can see a few artifacts emerge in the image, and by generation ten, you're definitely in trouble. I was quite surprised to find that there's very little visual penalty for recompressing a JPEG once, twice, or even three times. For each new generation, I opened and saved the previous generation with my standard JPEG compression factor of 15. I've been forced to do this when I couldn't find an uncompressed or high quality version of the image I needed, and I always wondered how much worse it made the image when I recompressed it.įor the recompression test, I started with the uncompressed, resized 384x384 Lena reference image. That is, opening a JPEG and re-saving it as a JPEG, including all the artifacts from the original compressed image in the recompression. I was also curious what the image quality and file size penalty was for recompressing a JPEG image. Here's a more complete breakdown of JPEG compression factor and file size for the 384x384 Lena image: Calculating the Bytes Per Pixel and BitRate of a JPEG Image How to. The original, uncompressed image size is 433 kilobytes.īeyond 50 percent compression factor, quality falls off a cliff, so I won't bother displaying anything higher. ![]() Note that I resized the image slightly (from 512x512 to 384x384) to keep the file sizes relatively small. So I performed a JPEG compression series using the Lena reference image*. Over the years, I've standardized on a JPEG compression factor of 15 I find that generally provides the best compromise between image quality and file size for most photographic images.Īlthough I've done some ad-hoc testing that pointed to compression factor 15 as the sweet spot before, I've never done a formal test. Just a warning to others considering it.A Comparison of JPEG Compression Levels and Recompression Locally it writes images fine, but once deployed I get a blank black image from it every time. UpdateĪrpanJpegEncoder appears to have issues once it's deployed - maybe I need to increase the trust level of the code, or perhaps something else is going on. It's likely that just wrapping an existing open source implementation, like Google's jpeg_optimizer in PageSpeed Tools - seemingly libjpeg underneath, would be the most efficient option. ![]() Filesizes also tend to be larger.īitMiracle's implementation is practically identical to the. Net built-in, but still is not as good as Gimp's or Photoshop's. It produces much higher quality JPEGs than the. I dug around and came across a project to implement a C# JPEG encoder by translating a C project over: But it is greater than 2MB So you will need to make the quality to 2/3.262.5. Assuming 10:1 compression, It will take 3.2MB. So if your image resolution is 40964096, it requires 409640962 raw bytes (2 because RGB565 is used), which equals 33554432 bytes 32MB raw. It's one of those lurking gotchas most people won't have scripted/automated, and you'll trip over it during some future server migration. Generally JPEG compresses the bitmap in the ratio 10:1. This lib is available on any dev machine with Visual Studio on it, but then you hit the server for the first time and it implodes with an obscure error. It requires a Visual Studio 2008 SDK lib installed. It has a special deployment burden on the server that's very easy to miss. It also still won't quite hit quality/compression levels of Photoshop or Google PageSpeed. But if you wanted high-detail subsampling at say, 50%, you have a larger challenge ahead. If you want to ignore subsampling, this is actually pretty convenient. In particular, its Chroma subsampling is set to high detail at 90% or above, then jumps down to a lower detail level - one that can introduce a lot of artifacts. It performs relatively solid jpeg compression. ImageMagick is the best choice I've found so far. I realize that's a partial answer but I'll expand on this once time allows. The ratio has to be well-defined to make shapes fit into different and distinct. You may not be aware of this fact, but every frame, digital video, canvas, responsive design, and image often has a rectangular shape that is exceptionally (or ratio). I'm now using an approach outlined here, that uses ImageMagick for the resize then jpegoptim for the final compression, with far better results. Use this ratio calculator to check the dimensions when resizing images. Net encoder built-in to the library (at least the default Windows library provided by Microsoft) is pretty bad: ![]()
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