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If, for example, one opens a compressed file in order to edit it. An MP3 music file in a wave editor, or a JPEG in Photoshop. When you 'save that file again, as the same filetype, does it 're-compress' the file each time it is saved. Or is it a separate process to 'encode' said file?
Or am I being simplistic and the two given examples are a completely different procedure?
I do both of these things quite a lot and I got to worrying that each time I'm working on something I'm degrading the quality further by re-squashing it each time. I generally try to work from a WAV in audio, but I'm not that knowledgeable when it comes to the image side of things. What is an uncompressed image? The equivalent of a WAV, Raw?
Some formats are lossy, some are lossless. Iirc JPEG is lossy, png or tiff can be lossless. I can't remeber what the audio equivalents are but I think wav is lossless.
JPEG is a lossy format itself irrespective of file compression (by compression I mean zip, etc.). The way the JPEG encoding/decoding works can be described as reducing the number of steps to go from light to dark. So if you start with an image with 256 steps then saving as JPEG at 75% quality will reduce the number of steps to 192. If you then open the file you still have 192 steps so providing you don't change the quality the encoding algorithm won't do anything different in that respect. There are some actions you can do that definitely don't alter the quality and some that do. The above is *very* simplistic but without going into cosine transforms and the like it's OK.
[url= https://improvephotography.com/2484/does-saving-a-jpeg-multiple-times-reduce-image-quality/ ]Here's a test[/url]
RAW images may be thought of as digital negatives which you then work on.
Remember - middle out
[url= https://www.thoughtco.com/jpeg-myths-and-facts-1701548 ]jpeg myths and facts[/url]
DavidB - Member
Remember - middle out
^^
This guy definitely *****.
The way the JPEG encoding/decoding works can be described as r...
That more like a description of GIF. JPEG is frequency domain - better thought of as reducing “texture” information.
Anyway, does it recompress? Short answer, yes (in most cases).