RGB PSNR over a 1,048,576 4x4 block compression torture test (random blocks from 81 test textures):
Near-opt BC7 (BC7E slower): 41.743
astcenc_thorough: 40.892
UASTC (veryslow)->ASTC 40.373
UASTC (veryslow)->BC7 39.965
UASTC (slower)->ASTC 40.163
UASTC (slower)->BC7: 39.782
UASTC (default)->ASTC 39.372
UASTC (default)->BC7: 39.171
UASTC (faster)->ASTC 39.269
UASTC (fastest)->ASTC 34.654
UASTC (fastest)->BC7 34.554
ispc_texcomp ASTC alpha_slow: 39.768
stb_dxt BC1 HIGHQUAL: 32.479
UASTC (slower)->BC1: 32.148
UASTC (fastest)->BC1 32.256
UASTC (slower)->ETC1: 30.956
UASTC (fastest)->ETC1: 30.113
UASTC (slower)->R11: 37.942
The 4096x4096 .PNG is here.
The EAC R11 format is R PSNR, and is included for comparison purposes.
Notice that the UASTC->BC1 quality actually increased when going from "slower" to "fastest" mode. This is because in "fastest" mode, almost all the blocks used UASTC mode 0, which is more compatible with BC1. (UASTC has 1-2 bits of BC1 hints per block that allow the UASTC block to be converted directly to BC1 blocks, skipping real-time encoding.)
Near-opt BC7 (BC7E slower): 41.743
astcenc_thorough: 40.892
UASTC (veryslow)->ASTC 40.373
UASTC (veryslow)->BC7 39.965
UASTC (slower)->ASTC 40.163
UASTC (slower)->BC7: 39.782
UASTC (default)->ASTC 39.372
UASTC (default)->BC7: 39.171
UASTC (faster)->ASTC 39.269
UASTC (fastest)->ASTC 34.654
UASTC (fastest)->BC7 34.554
ispc_texcomp ASTC alpha_slow: 39.768
stb_dxt BC1 HIGHQUAL: 32.479
UASTC (slower)->BC1: 32.148
UASTC (fastest)->BC1 32.256
UASTC (slower)->ETC1: 30.956
UASTC (fastest)->ETC1: 30.113
UASTC (slower)->R11: 37.942
The 4096x4096 .PNG is here.
The EAC R11 format is R PSNR, and is included for comparison purposes.
Notice that the UASTC->BC1 quality actually increased when going from "slower" to "fastest" mode. This is because in "fastest" mode, almost all the blocks used UASTC mode 0, which is more compatible with BC1. (UASTC has 1-2 bits of BC1 hints per block that allow the UASTC block to be converted directly to BC1 blocks, skipping real-time encoding.)