kc3-lang/libjpeg-turbo

2024-06-18T13:06:30

TJBench: Test end-to-end grayscale comp./decomp. Because the TurboJPEG API originated in VirtualGL and TurboVNC as a means of compressing from/decompressing to extended RGB framebuffers, its earliest incarnations did not handle grayscale packed-pixel images. Thus, TJBench has always converted the input image (even if it is grayscale) to an extended RGB source buffer prior to compression, and it has always decompressed JPEG images (even if they are grayscale) into an extended RGB destination buffer. That allows TJBench to benchmark the RGB-to-grayscale and grayscale-to-RGB color conversion paths used by VirtualGL and TurboVNC when grayscale subsampling (AKA the grayscale JPEG colorspace) is selected. However, more recent versions of the TurboJPEG API handle grayscale packed-pixel images, so it is beneficial to allow TJBench to benchmark the end-to-end grayscale compression and decompression paths. This commit accomplishes that by adding a new command-line option (-gray) that causes TJBench to use a grayscale source buffer (which only works if the input image is PGM or grayscale BMP), to decompress JPEG images (even if they are full-color) into a grayscale destination buffer, and to save output images in PGM or grayscale BMP format.