Trying to understand losses in jpg compression

by Martin Argerami   Last Updated December 02, 2017 19:18 PM

I have a bunch of jpegs taken with a Nikon D3200 at 6016 x 4000. They weigh between 9M and 12M each.

To try and reduce space a bit, I compressed copies with the default Windows utility, and the new images are 3411 x 2268 and weigh between 0.4M and 0.5M. That is, there's been a 20:1 reduction in file size, while pixelwise the reduction is 3:1.

I look at the images in my screen, even zooming several times, and I struggle to see a difference in quality; I'm aware than I'm no expert, though.

So my questions are, what is a more normal rate for jpeg compression: 6016 x 4000 at 10M, or 3411x 2268 at 0.5M? Is there anything I should be worried that I'm losing from the original files?



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