# Help me understand image compression
**URL:** https://meta.discourse.org/t/help-me-understand-image-compression/274297
**Category:** Support
**Created:** [August 8, 2023, 3:32am UTC](https://meta.discourse.org/t/help-me-understand-image-compression/274297 "2023-08-08T03:32:12Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@Brandon007](https://meta.discourse.org/u/Brandon007)
#### Post date: [August 8, 2023, 3:32am UTC](https://meta.discourse.org/t/help-me-understand-image-compression/274297/1 "2023-08-08T03:32:12Z")
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?
Here are my settings to confirm:
`max image size kb` = 4096
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### Author:  [@pfaffman](https://meta.discourse.org/u/pfaffman)
#### Post date: [August 8, 2023, 3:35am UTC](https://meta.discourse.org/t/help-me-understand-image-compression/274297/2 "2023-08-08T03:35:37Z")
> [@Brandon007](#):
>
> appears the `composer media optimization image bytes optimization threshold` sets the precedent.
Maybe set that threshold very low?
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### Author:  [@Jagster](https://meta.discourse.org/u/Jagster)
#### Post date: [August 8, 2023, 7:57am UTC](https://meta.discourse.org/t/help-me-understand-image-compression/274297/3 "2023-08-08T07:57:17Z")
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?
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### Author:  [@Canapin](https://meta.discourse.org/u/Canapin)
#### Post date: [August 8, 2023, 8:10am UTC](https://meta.discourse.org/t/help-me-understand-image-compression/274297/4 "2023-08-08T08:10:48Z")
> [@Brandon007](#):
>
> However, it appears the `composer media optimization image bytes optimization threshold` sets the precedent.
After testing, it is correct 🙂
I believe @pfaffman’s solution is the way to go to achieve what you want.
> [@Jagster](#):
>
> but what does `client-side optimization` mean in practice
Long explanation: [Faster (and smaller) uploads in Discourse with Rust, WebAssembly and MozJPEG](https://blog.discourse.org/2021/07/faster-user-uploads-on-discourse-with-rust-webassembly-and-mozjpeg/)
Short explanation: large images are resized/recompressed on your device (via javascript) before they are sent to Discourse.
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### Author:  [@Jagster](https://meta.discourse.org/u/Jagster)
#### Post date: [August 8, 2023, 8:15am UTC](https://meta.discourse.org/t/help-me-understand-image-compression/274297/5 "2023-08-08T08:15:26Z")
> [@Canapin](#):
>
> before they are sent to Discourse
Right, it works to that direction. Well, that is much more smarter way than optimization to other direction 🤦♂️
Thanks.
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### Author:  [@Brandon007](https://meta.discourse.org/u/Brandon007)
#### Post date: [August 8, 2023, 12:46pm UTC](https://meta.discourse.org/t/help-me-understand-image-compression/274297/6 "2023-08-08T12:46:14Z")
> [@Brandon007](#):
>
> composer media optimization image bytes optimization threshold
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.
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### Author:  [@Falco](https://meta.discourse.org/u/Falco)
#### Post date: [August 8, 2023, 6:17pm UTC](https://meta.discourse.org/t/help-me-understand-image-compression/274297/7 "2023-08-08T18:17:11Z")
> [@Brandon007](#):
>
> I’m not quite sure I understand image compression in Discourse. Straighten me out.
I find the diagram at the [blog post](https://blog.discourse.org/2021/07/faster-user-uploads-on-discourse-with-rust-webassembly-and-mozjpeg/) helpful:
X → `composer media optimization image bytes optimization threshold`
Y → `composer media optimization image resize dimensions threshold`
Z → `composer media optimization image resize width target`
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### Author:  [@Canapin](https://meta.discourse.org/u/Canapin)
#### Post date: [November 9, 2025, 2:23pm UTC](https://meta.discourse.org/t/help-me-understand-image-compression/274297/8 "2025-11-09T14:23:04Z")
> [@Falco](#):
>
> 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:
> `composer_media_optimization_image_dimensions_resize_threshold`
The right name is “Composer media optimization image resize dimensions threshold” (“resize dimensions”, not “dimensions resize”).
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### Author:  [@system](https://meta.discourse.org/u/system)
#### Post date: [December 9, 2025, 2:23pm UTC](https://meta.discourse.org/t/help-me-understand-image-compression/274297/9 "2025-12-09T14:23:54Z")
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