Photoshop downsizing image

Question

I am having an issue lately with photoshop downsizing my image quality considerably. I have tried figuring out if I have somehow changed a setting somewhere, but cannot see that I am doing anything any differently.

For instance, if I upload an image from my camera that is 8MB JPEG file and then edit it, and save it, without resizing it at all, and on saving it, if I choose highest quality, it will maybe come out at 2.01MB.

I cannot understand what is happening here. It has only started doing this recently.

I had wondered if there was some sort of optimization default setting that came with an update or something, but so far, I cannot track anything down. I need to work and save in the highest possible file size at the moment for multiple reasons.

Has anyone had this issue, or do you know of something I am missing here?

Thank you.

D Fosse · Answer

You need to understand that the jpeg file format uses very aggressive data compression to reduce file size on disk. When you open a jpeg it's decompressed back to original size - but not the original state. Jpeg compression is destructive, non-reversible and cumulative. A jpeg is always an end product, not to be worked on again.

Jpeg compression survives in spite of all the drawbacks because it is incredibly effective. An average file can shrink to 2 - 5% of original size, with little visual impact (although it's there).

Any file format is a storage format. When the file is open, it doesn't have a file format - it's just an image in memory. The file format is a recipe for packaging the file on disk.

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