bug: Downscaling re-encodes PNG losslessly, so large PNGs still exceed the size limit

[monon999]

Version: 2.0.23

Describe the Bug

In imageDownscale.ts, only JPEG input is re-encoded as JPEG (quality 0.92); PNG and WebP are written back out as PNG to stay lossless.

With the default "Max image size" of 2048 px, a 5120x5120 PNG is correctly downscaled, but the resulting PNG is still over 10 MB, so it is rejected by the size check with image.png exceeds the 10MB limit.

Since the vision tower resamples to a fixed resolution anyway, keeping a lossless PNG doesn't buy any accuracy — it only inflates the base64 payload and the context. Encoding to JPEG when the image has no alpha channel, or producing both and keeping the smaller one, would avoid this.

Steps to Reproduce

1. Keep "Max image size" at the default 2048 px.
2. Prepare a detailed 5120x5120 PNG (mine is 23.3 MB).
3. Copy it to the clipboard and paste it into the chat input.
4. It is rejected with "image.png exceeds the 10MB limit", even though it was downscaled to 2048 px first.

Screenshots / Logs

Operating System

• MacOS
• Windows
• Linux

[Vect0rM]

Thank you for the report and for reading through imageDownscale.ts — you nailed it. Anything that isn't JPEG is currently written back as lossless PNG regardless of content, so a detailed 2048 px PNG easily stays over the 10 MB limit the downscale was supposed to get you under.

The fix in the next release does what you suggested: the downscaler now checks whether the image actually has transparency. Opaque images are encoded as JPEG (or keep PNG when the lossless version is already small enough), and PNG is only kept when there's an alpha channel to preserve. Your 5120x5120 case comes out well under the limit with that.

We truly appreciate your help in making Atomic Chat better!