I’m not quite sure I understand image compression in Discourse. Straighten me out.
I uploaded a 2392x884 214kb image and the resolution stayed the same.
I uploaded a 3200x1800 1.7mb image and the resolution scaled down to the composer media optimization image resize dimensions threshold setting.
With the setting at 1280 wide, I expected all images to be scaled down to that width. However, it appears the composer media optimization image bytes optimization threshold sets the precedent.
My first image was under 524kb, so it wasn’t altered.
The second image was over 524kb, so it was altered.
If I follow correctly, is there a way to reduce all uploaded files to 1280 wide?
Because topic is named in very general way I don’t start new topic but what does client-side optimization mean in practice - an OS of device will make its mind if it will do or not something? But that will lead to the situation where a giga big image must transfer to a client before its size will change to decent scale, or am I totally lost now?
I did try that last night before posting and that does seem to be the key.
Here’s the deal:
composer media optimization image bytes optimization threshold
524288 (default) setting = Good quality image, 1920px.
200000 setting = Degraded image, since it drops resolution from 1920 to 1280.
So this morning, on my desktop, I took the same image (2392px), resized it to 1280px and it’s degraded a bit as well. So the degradation I can’t get around. It’s a product of dropping the resolution from 2392px to 1280px. It did reduce the image size by four times though.
Note: .HEIC photos don’t play by the same rules. A 4032px .HEIC was reduced to 2016px. So I don’t know how that setting was applied.
All in all, I think I get it, after a little trial and error. I think I’ll use the default settings, I really like the extra crispness of a 1920px photo over the 1280px.
Hopefully, this helps someone else out.
Edit: I dropped composer media optimization image bytes optimization threshold from the default of 524288 to 200000. I noticed, uploading a basic .png file at 1220px @ 414kb only resulted in a file size of 406kb. By reducing the setting above to 200000, the file size was reduced from 414kb to 201kb. The resolution was unchanged.
So I don’t know what else is being triggered with that setting, but clearly something else to further reduce the image size.
X → composer media optimization image bytes optimization threshold
Y → composer media optimization image resize dimensions threshold
Z → composer media optimization image resize width target
I’m afraid I must be dumb for not quite understanding this part when looking at the settings’ definitions:
composer_media_optimization_image_dimensions_resize_threshold: default 1920
Minimum image width to trigger client-side resize
composer_media_optimization_image_dimensions_resize_target: default 1920
Images wider than composer_media_optimization_image_dimensions_resize_threshold will be resized to this width.
Must be ≥ that threshold.
This part specifically:
Must be ≥ that threshold.
Shouldn’t it be ≤ instead? I don’t understand why it would resize to a higher width value than the threshold
Also, in the same setting’s description, the first setting is misnamed:
but what does 
