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I have a 700Kb JPEG file (white cardboard texture) that I'm using as a background on a website.
A file this large takes too long to load for snappy page hits. I don't need the full resolution, a reduction in image quality is fine, but I do need to keep the JPEG the same size (to fill the entire screen).
What would be a good free PC or web utility that would allow me to modify a JPEG as described? I'd rather not use Photoshop or other professional software.
You can use Gimp to open the JPEGs and save them with less quality.
See in Make JPGs smaller.
You can make your jpegs smaller without changing the pixel width of the image.
In the JPEG Save Dialog, you can opt for GIMP defaults which reduce the size quite a bit, without hurting the visual quality in a way that you can detect. This would be the safest and quickest thing to do.
On Windows I'd recommend FileOptimizer On Mac I'd recommend ImageOptim
Both use JPEGOptim as a backend to try to losslessly reduce the jpeg size, and if that's not good enough should allow you to set a minimum quality level to let you squeeze the file even smaller.
Something else to look into would be a progressive JPEG. A progressive JPEG loads a very low resolution copy of the image, and then progressively loads more detail. This gives you a snappy response, and all the quality you might want. I know that imageoptim can make progressive JPEGs, I'm not sure about FileOptimizer, but since they both use JPEGOptim as a backend, I would not be surprised.
1. You could always convert your background from a .jpeg to a .png which would help reduce file size. There are even some PNG compression tools such as:
2. Try using Imagemagick that converts and can modify images. To learn how to compress files you can go here. Imagemagick can convert files from .jpeg to .png by mogrify -format jpg *.png.
3. As stated always download Gimp and open it up. If its one image it would be easier to just install a program than to reference code.
4. You did request a website that would prevent you from coding and downloading. Imagemagick does have a site called ImageMagick Studio that you can upload the file to or convert from your site.
5. This topic has been discussed on SO: Recommendation for compress jpg files with Imagemagick
6. Ifranview graphic viewer.
Another dedicated free tool for this is RIOT--Radical Image Optimization Tool.
With RIOT, you get a large instant preview of how adjusting different image quality parameters would affect the final output, and it dynamically shows you the resulting file size so you can decide when to stop. And, as a bonus, RIOT can also work from within a lot of your favorite free image editing tools (for example, Gimp).
Another thing you should do in addition to changing the image quality, though, is strip out all of the metadata and other unnecessary junk that can bloat image files.
