Module yuv

Utilities for doing the YUV -> RGB conversion The images are encoded in the Y’CbCr format as detailed here: https://en.wikipedia.org/wiki/YCbCr so need to be converted to RGB to be displayed To do the YUV -> RGB conversion we need to first decide how to map the yuv values to the pixels The y buffer is the same size as the pixel buffer so that maps 1-1 but the u and v buffers are half the size of the pixel buffer so we need to scale it up The simple way to upscale is just to take each u/v value and associate it with the 4 pixels around it e.g. for a 4x4 image:

|||||| |yyyy| |yyyy| |yyyy| |yyyy| ||||||

||||||| |uu|vv| |uu|vv| |||||||

Then each of the 2x2 pixels would match the u/v from the same quadrant

However fancy upsampling is the default for libwebp which does a little more work to make the values smoother It interpolates u and v so that for e.g. the pixel 1 down and 1 from the left the u value would be (9u0 + 3u1 + 3u2 + u3 + 8) / 16 and similar for the other pixels The edges are mirrored, so for the pixel 1 down and 0 from the left it uses (9u0 + 3u2 + 3u0 + u2 + 8) / 16

Functions

clip 🔒

This function has been rewritten to encourage auto-vectorization.

fill_rgb_buffer_fancy 🔒

Fills an rgb buffer with the image from the yuv buffers Size of the buffer is assumed to be correct BPP is short for bytes per pixel, allows both rgb and rgba to be decoded

fill_rgb_buffer_simple 🔒

Simple conversion, not currently used but could add a config to allow for using the simple

fill_rgba_row_simple 🔒

fill_row_fancy_with_1_uv_row 🔒

fill_row_fancy_with_2_uv_rows 🔒

Fills a row with the fancy interpolation as detailed

get_fancy_chroma_value 🔒

mulhi 🔒

_mm_mulhi_epu16 emulation

set_pixel 🔒

yuv_to_b 🔒

yuv_to_g 🔒

yuv_to_r 🔒