From bcec339b01c1254404b238441a38b8041ea6ab19 Mon Sep 17 00:00:00 2001 From: Urvang Joshi Date: Wed, 12 Dec 2012 14:03:44 -0800 Subject: [PATCH] Lossless bitstream clarification: Clarify what the pixels of a color transform image are. Change-Id: I720248b5417857468d54952440cf1bae6c091042 --- doc/webp-lossless-bitstream-spec.txt | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/doc/webp-lossless-bitstream-spec.txt b/doc/webp-lossless-bitstream-spec.txt index 7922acd6..51d0746d 100644 --- a/doc/webp-lossless-bitstream-spec.txt +++ b/doc/webp-lossless-bitstream-spec.txt @@ -604,9 +604,11 @@ to entropy coding, and three further roles related to transforms. 4. Color indexing image. An array of up to 256 ARGB colors is used for transforming a green-only image, using the green value as an index to this one-dimensional array. - 5. Color transformation image. Defines signed 3.5 fixed-point - multipliers that are used to predict the red, green, and blue - components, to reduce entropy. + 5. Color transform image. It is created by `ColorTransformElement` values + (defined in [Color Transform](#color-transform)) for different blocks of + the image. Each `ColorTransformElement` `'cte'` is treated as a pixel whose + alpha component is `255`, red component is `cte.red_to_blue`, green + component is `cte.green_to_blue` and blue component is `cte.green_to_red`. To divide the image into multiple regions, the image is first divided into a set of fixed-size blocks (typically 16x16 blocks). Each of these