Optimize the lib ColorThief

Collapse will use the method in ColorThief to calculate the theme color of the background image when switching game region. But the performance of this third-party library is extremely bad. It takes 169 ms when parsing the official launcher image (1280x730), and only more when parsing custom larger images.

Get palette list with colorCount=255 and quality=3, Same parameters as collapse.

Ignore the time consumption and memory allocation for image decoding

ColorThief can be optimized as follows:

• Use pointer to get pixels with color instead of Bitmap.GetPixel
• Use one-dimensional arrays byte[] to store pixels instead of interleaved arrays byte[][]
• Directly specify the number of pixels when splitting the vbox, instead of repeated calculations

After I optimized the code, the time consumed and the amount of memory allocated were greatly reduced. To make it simpler to write the code, each pixel of the image will be included, so the parameters: colorCount=255 and quality=1.

Could I remove the submodule ColorThief and commit code in this project?

[neon-nyan]

Hi @Scighost,

Thank you for the information. As per your suggestion and some additional changes including:

• Enumerate the pixel (only took R, G and B channel) into a single int.
• Pass the IEnumerable<int> into Mmcq.Quantize() and processing the pixels on-the-fly.

By enumerating the pixel directly instead of pre-allocating it first with this “v2” code, we got a really significant reduction memory allocation from initially 352 MB to 21.65 MB at “v1” changes and finally 130 KB at “v2” changes with quality=1

Method	Mean	Error	StdDev	Ratio	Allocated	Alloc Ratio
GetPalleteOldQuality8	458.494 ms	7.2605 ms	6.7915 ms	0.121	44205.29 KB	0.125
GetPalleteOldQuality4	918.912 ms	7.1911 ms	6.7266 ms	0.243	88262.94 KB	0.250
GetPalleteOldQuality2	1,870.017 ms	11.8865 ms	11.1187 ms	0.495	176398.48 KB	0.500
GetPalleteOldQuality1	3,781.903 ms	13.0441 ms	10.8924 ms	1.000	352658.34 KB	1.000
GetPalleteNewAndFixQuality8	1.593 ms	0.0163 ms	0.0153 ms	0.000	130.38 KB	0.000
GetPalleteNewAndFixQuality4	4.799 ms	0.0285 ms	0.0253 ms	0.001	130.38 KB	0.000
GetPalleteNewAndFixQuality2	17.884 ms	0.2137 ms	0.1999 ms	0.005	130.4 KB	0.000
GetPalleteNewAndFixQuality1	71.567 ms	0.8822 ms	0.8252 ms	0.019	130.45 KB	0.000

Note

The quality=1 on this new “v2” code has a bit performance degradation compared to the last modification due to enumeration overhead. But the rest with quality > 1 got a bit performance improvement. Hope this can be improved in the future.

That being said, thank you for your amazing contribution on this optimization! Please allow me to merge the changes into ColorThief Submodule repo and close this issue.

[Scighost]

Good job!

There are two more small areas that can be optimized.

• Initialize the color vector space directly from the image’s memory area, skipping the step of passing pixel values using byte arrays.
• After setting quality, only pixels in the x-direction are currently sampled, and pixels in the y-direction should be sampled as well.

Of course, it is very good now, and I will not pull request for ColorThief again.