Also, the standard for most (dunno for Spotify) is to have a .jpg
95% quality is fine, 100% is useless, under80% is bad
And non progressive
Could you explain on which evidence these figures are based?
To me it looks as though your percentages are purely personal taste and by far no "standard".
I was looking for the sweet spot between quality and size. So after reading what I can this is how I understand it : From 95 to 100% you will only double or triple the size for no perceptible improvement, so no need to have a 2mb file when a 600Ko is barely the same, with a 50 000 tracks library, it will make a 70+Go difference with embedded covers
Under 80% it start to show compression artifact if you look into details, and the size isn’t really better (from 600 to 500ko won’t be a huge improvement)
So the sweet spot for us humans with human eyes, the good ratio quality X size, seem to be 80 - 95%
One aspect is the amount of storage space saved per file, or in total.
On the other hand, the money savings you make are very minimal.
If you calculate the costs for your saved example 70 GB, then currently on a HDD you would save about 2 Euro. On a fast SSD about 8 Euro and on an external USB stick about 10 Euro.
In my opinion, it's not worth compressing an embedded picture any further.
Neither to 80% nor to 95%.
Remember: once quality has been reduced, it can never be regained.
If you're really concerned about saving space, I would recommend a solution like 1 x external file in very good quality per album directory (which brings other disadvantages.)
It is probably an ok rule of thumb, but higher resolution negates most of the artifacts, So I usually save JPGs at 4000x4000 and adjust down to around 600 to 800 kb, instead of 800x800 at the same file size. And even tough that may be setting the quality slider down to 25% instead of 90%, the visual quality is remarkably better.
While I agree that the saved space is usually negligible, there are other aspects to consider as well when it comes to the resolution and file size of (embedded) pictures.
- If the image size is >~16MB, the image cannot be embedded into flac files
- Embedding huge art in every song may increase the time it takes music server or library software to scan the files
- Having huge art in general may decrease the performance of music servers (Navidrome, lms etc.) when browsing the library as loading in such huge images can make the experience choppy
Personally I visually inspect each image at 100% resolution before adding it and my usual goal is 1400px JPGs with >85 quality (many of the 3000px or 4000px images available on the web are upscaled and offer 0 advantages over their 1400px or even 800px counterparts). If there are higher quality images available, I use these (up to 4000px, as long as they remain <10MB in size so they don’t slow down or break other services that access my files).
Instead of embedding these art files into each song (which I consider to be a waste of space), I place one image in each album folder as Cover.jpg. All players and servers I use support this.
Decades ago when disk-space was very important I made some optical tests with resolution and compression factor in relation to visual quality and size.
I came to the conclusion that if you want to get a picture of for instance 200 kb size it is much better to use a high resolution and strong compression that a lower resolution and lower compression.
But:
Album covers in the Internet that have a really high resolution like 4000 x 4000 are often just blown up without any gain of quality of the high resolution. I sometimes noticed covers of older albums that had a really bad quality and an original resolution of about 200 x 200 and were offered at 1500 x 1500.
Also the pictures mostly are not really camera-photos but graphically designed. It does really not make much sense to save a jpg with a few colors at highest possible quality.