YCCA Subsampling for Unity

YCCA subsampling is a set of lossy texture compression formats inspired by ChromaPack. You can choose bpp (bits per pixel) from 12, 14 and 24. The main difference from ChromaPack is that they support alpha.

Read before trying this repository!

• Use ETC2 on mobile platforms where OpenGL ES 3.0 is supported.
• Use ASTC or DXTC for PCs.
• Try ETC/PVRTC and (half-resolution) alpha mask.
• Try this repository only if none of the above satisfies your requirements.

Overview

• RGB is encoded into YCgCo, which can be decoded effectively.
  • Other color spaces (e.g. YCbCr which is used in ChromaPack) can be supported by slightly modifying the encoder and decoder, but currently they are not supported.
  • Note that effectiveness is not certain, because YCgCo and YCbCr are equivalent in decoding time where matrix multiplication is fast enough.
• Y channel is stored without compression (Alpha 8).
• Cg Co and Alpha channels are stored in compressed formats, such as:
  • 4 bpp block compression formats (ETC1, PVRTC or DXT1).
  • RGB24 and RGB565 with scaling-down.

How to use

1. Click the menu "Window/YCgACo Editor".
2. Select source image, and then click "Generate Y, CgACo and Material".
3. Change format and quality, and click "Apply" if you need.

Dummy PNG + user data + postprocess

YCgACo Editor does not produce PNG file which contains texture data. Instead, it produces 1 pixel dummy PNG files, and meta files which contains the source image GUID and target compression format as AssetImporter.userData. The dummy PNGs are imported as actual encoded textures when they are post-processed by YCgACoPostprocessor.

Examples

• Assets/YccaSubsamplingTest/Circle/Circle.png 128x128 pixels

TODO

• Reimporting encoded textures when the source texture is updated.
• Support YCbCr and other color spaces (e.g. PCA-based color space).
• Scaling CgACo textures in order to achieve flexible bits per pixel.
• Writing a decoder as a matrix multiplication and measure performances.