Compressing a really really big image?

[artistgrrl]

Hey all, I am baaaaaack....

Haven't used XnView in a while but found it necessary to fire it up again. New version does seem easier to use. I had my old forum thread bookmarked and followed that to refresh my memory.

I have a large - 8000 x 8000 - fractal image that I wanted to keep kind of large in order to show intricate details. I can't seem to get it compressed down to any reasonable filesize. BMP was gigantic of course, PNG not much better. XnView's optimized JPG won't bring an 85 mb image down to any less than 50 mb without graininess starting to appear; I tried different settings but 95 % quality is about as low as I can go. I really should have it streamlined right down to 5 mb or so, 10 at most, if that is possible without sacrificing detail...

Thanks in advance

Artist Grrl

[cday]

Have you tried down-sampling the image using Image | Resize... ?

With PNG, did you use maximum compression? (still loss-less but slower, I think).

Saving as JPEG2000 (.jp2 extension) will normally produce a rather smaller file than JPG, with compression artifacts that may be less noticeable.

Finally, if your image could be converted to black and white, you should get a very large reduction by saving as a TIFF with Fax compression...


[Edited]

[Drahken]

You could try WEBP or JXR (jpeg XR) formats, they'll probably get a bit better than the JPG.
If your image is 50Mb in JPG format though, there's no way you're going to get it even close to 10MB without resizing it much, MUCH smaller. Compressing an 85MB image down to 5~10MB without sacrificing either resolution or quality is just not possible anywhere in the known universe. I think 40MB or so is the best you can hope for.

The only other thing you might do is crop the pic down instead of resizing it. You would give up much of the image, but you would be able to retain detail in the remaining portion.
I don't know exactly what you're trying to do with the pic, but your best bet may be to make 2 files. Either crop or resize the pic to use as a 5~10MB thumbnail/sample file, then offer up the full sized one for people who want a better look.

The only other route would be to cut the image into several smaller images, so that you'd have 5 10MB images instead of 1 50MB one.