Implement binary for accuracy testing

[FreezyLemon]

I had the idea a while ago, but never really got around to implementing it. I'm PRing in the current state to get some feedback, as I'm not 100% sure on where to take this and how to make it more useful.

One of the biggest questions is how to properly test the algorithm accuracy. So far, I've tried converting the source (sRGB) image with imagemagick via convert pic_srgb.png -colorspace RGB pic_rgb.png. But when comparing the converted image to a LinearRgb conversion (current code), you'll see that the error is relatively large (and that even turning fastmath off won't help much). Not sure what's going on there.

Run with cargo run --features build-acctest --bin acctest -r

[Luni-4]

What is the status of this PR?

[FreezyLemon]

At a glance:

• comparison image paths are hardcoded, the binary should probably handle CLI parameters
• At the moment, the expected output images are created outside the Rust code by external tools. This should be integrated
• It should be checked/verified that the imagemagick conversions are accurate (or at least more accurate than ours). Maybe need to change to another tool to create the images we compare against.

[Luni-4]

* comparison image paths are hardcoded, the binary should probably handle CLI parameters

I agree about the CLI parameters for image paths

* At the moment, the expected output images are created outside the Rust code by external tools. This should be integrated

I also agree with this change

* It should be checked/verified that the imagemagick conversions are accurate (or at least more accurate than ours). Maybe need to change to another tool to create the images we compare against.

As intermediate goal, we can produce images which are equals to the one created with imagemagick and then evaluate if the process used in creating those images is correct or not. I think it would be better having everything in the same tool initially and split it up eventually

[FreezyLemon]

As intermediate goal, we can produce images which are equals to the one created with imagemagick and then evaluate if the process used in creating those images is correct or not. I think it would be better having everything in the same tool initially and split it up eventually

I am not sure if I understand you correctly. The original goal was to

1. Take an input image
2. Convert it with yuvxyb
3. Compare the converted image to a reference
4. Visualize the relative differences between the two

The big question is: What to use as a reference? I used imagemagick to create the references for this draft, but it seems to have a significant delta to our conversions. This could indicate three things in my mind:

• I made a mistake when creating the reference images,
• the yuvxyb conversion is bad, or
• imagemagick's conversion is less accurate than expected

I don't really know enough about imagemagick (or possible alternatives) to solve this without some significant time investment.

[Luni-4]

Ok now I better see the problem, thanks!

Can we use the test card as minimal case in order to isolate where deltas are?

For example, if we have 3 frameworks, we can pass the test card to these 3 frameworks as input obtaining 3 output images. If these output images are all equals to each other, then it means our algorithm is wrong. If there are differences among them, we can discover what are these differences, and analyzing their algorithms, we can discover something more.

I do not know if this procedure is feasible or if I've figured out correctly the issue.