Resized Image resulted in increase in file size

[omodia]

Describe the bug
Resizing of files resulted in an increase in the file size rather than decrease.

Software version
2.3.0

Operating System information

• OS: Windows
• Version 11

To Reproduce
Steps to reproduce the behavior:

1. Open the attached webp file in zip below
2. Check lossless option.
3. Resize - Keep aspect ratio: 50% width and height.
4. Output format : same as input or select webp
5. Compress and see the result

Expected behavior
A decrease in the original file size as the image is also being decreased to 50% of its original width and height

Screenshots

[Lymphatus]

Unfortunately, this is somehow expected. Let me explain a little bit more.
Resizing an image is always* a lossy operation: you are reducing the pixels of the image, so you naturally lose something. If you check the "Lossless" option, Caesium will resize the image, encode it with the best quality possible and then applying a lossless optimization. This to minimize the loss of quality for the image.
If your image was well optimized before, resizing then encoding it at best quality can result in a bigger image, because the lossless optimization will not shred that much size.

So for example:

• Initial image is 200 Kb and well optimized
• Resize at 50%, encode it at 100 quality results in a 300Kb image
• Optimize it for a 290Kb final image

A possible solution from your side is to uncheck the "lossless" option and save it at your desired quality, since you are losing quality anyway by resizing.
On the other hand, I'm thinking to disable to lossless option for resizing or providing a warning for this behaviour.

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*This is not always true, but we are talking about very specific cases

[omodia]

Thanks for the explanation. I now have an idea of how it works.