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WebP/Lossy: It's 'macroblock', not 'metablock'

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Somehow my brain decided to change the name of this concept.
Not sure why, the spec consistently uses 'macroblock'.

No behavior change.
This commit is contained in:
Nico Weber 2023-05-28 11:30:03 -04:00 committed by Andreas Kling
parent b8a097f74b
commit d15ae9fa93
Notes: sideshowbarker 2024-07-17 01:00:06 +09:00 
Author: https://github.com/nico
Commit: https://github.com/SerenityOS/serenity/commit/d15ae9fa93
Pull-request: https://github.com/SerenityOS/serenity/pull/19109
2 changed files with 25 additions and 25 deletions
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46
Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.cpp
View file

@ -24,20 +24,20 @@
// * A tiny bit of uncompressed data, storing image dimensions and the size of the first compressed chunk of data, called the first partition
// * The first partition, which is a entropy-coded bitstream storing:
// 1. A fixed-size header.
// The main piece of data this stores is a probability distribution for how pixel values of each metablock are predicted from previously decoded data.
// The main piece of data this stores is a probability distribution for how pixel values of each macroblock are predicted from previously decoded data.
// It also stores how may independent entropy-coded bitstreams are used to store the actual pixel data (for all images I've seen so far, just one).
// 2. For each metablock, it stores how that metablock's pixel values are predicted from previously decoded data (and some more per-metablock metadata).
// 2. For each macroblock, it stores how that macroblock's pixel values are predicted from previously decoded data (and some more per-macroblock metadata).
// There are independent prediction modes for Y, U, V.
// U and V store a single prediction mode per macroblock.
// Y can store a single prediction mode per macroblock, or it can store one subblock prediction mode for each of the 4x4 luma subblocks.
// * One or more additional entropy-coded bitstreams ("partitions") that store the discrete cosine transform ("DCT") coefficients for the actual pixel data for each metablock.
// Each metablock is subdivided into 4x4 tiles called "subblocks". A 16x16 pixel metablock consists of:
// 0. If the metablock stores 4x4 luma subblock prediction modes, the 4x4 DC coefficients of each subblock's DCT are stored at the start of the macroblock's data,
// * One or more additional entropy-coded bitstreams ("partitions") that store the discrete cosine transform ("DCT") coefficients for the actual pixel data for each macroblock.
// Each macroblock is subdivided into 4x4 tiles called "subblocks". A 16x16 pixel macroblock consists of:
// 0. If the macroblock stores 4x4 luma subblock prediction modes, the 4x4 DC coefficients of each subblock's DCT are stored at the start of the macroblock's data,
// as coefficients of an inverse Walsh-Hadamard Transform (WHT).
// 1. 4x4 luma subblocks
// 2. 2x2 U chrome subblocks
// 3. 2x2 U chrome subblocks
// That is, each metablock stores 24 or 25 sets of coefficients.
// That is, each macroblock stores 24 or 25 sets of coefficients.
// Each set of coefficients stores 16 numbers, using a combination of a custom prefix tree and dequantization.
// The inverse DCT output is added to the output of the prediction.
@ -138,13 +138,13 @@ enum class SegmentFeatureMode {
};
struct Segmentation {
bool update_metablock_segmentation_map { false };
bool update_macroblock_segmentation_map { false };
SegmentFeatureMode segment_feature_mode { SegmentFeatureMode::DeltaValueMode };
i8 quantizer_update_value[4] {};
i8 loop_filter_update_value[4] {};
u8 metablock_segment_tree_probabilities[3] = { 255, 255, 255 };
u8 macroblock_segment_tree_probabilities[3] = { 255, 255, 255 };
};
ErrorOr<Segmentation> decode_VP8_frame_header_segmentation(BooleanDecoder&);
@ -197,7 +197,7 @@ struct FrameHeader {
CoefficientProbabilities coefficient_probabilities;
bool enable_skipping_of_metablocks_containing_only_zero_coefficients {};
bool enable_skipping_of_macroblocks_containing_only_zero_coefficients {};
u8 probability_skip_false;
};
@ -239,9 +239,9 @@ ErrorOr<FrameHeader> decode_VP8_frame_header(BooleanDecoder& decoder)
TRY(decode_VP8_frame_header_coefficient_probabilities(decoder, header.coefficient_probabilities));
// https://datatracker.ietf.org/doc/html/rfc6386#section-9.11 "Remaining Frame Header Data (Key Frame)"
header.enable_skipping_of_metablocks_containing_only_zero_coefficients = TRY(L(1));
dbgln_if(WEBP_DEBUG, "mb_no_skip_coeff {}", header.enable_skipping_of_metablocks_containing_only_zero_coefficients);
if (header.enable_skipping_of_metablocks_containing_only_zero_coefficients) {
header.enable_skipping_of_macroblocks_containing_only_zero_coefficients = TRY(L(1));
dbgln_if(WEBP_DEBUG, "mb_no_skip_coeff {}", header.enable_skipping_of_macroblocks_containing_only_zero_coefficients);
if (header.enable_skipping_of_macroblocks_containing_only_zero_coefficients) {
header.probability_skip_false = TRY(L(8));
dbgln_if(WEBP_DEBUG, "prob_skip_false {}", header.probability_skip_false);
}
@ -256,11 +256,11 @@ ErrorOr<Segmentation> decode_VP8_frame_header_segmentation(BooleanDecoder& decod
// Corresponds to "update_segmentation()" in section 19.2 of the spec.
Segmentation segmentation;
segmentation.update_metablock_segmentation_map = TRY(L(1));
segmentation.update_macroblock_segmentation_map = TRY(L(1));
u8 update_segment_feature_data = TRY(L(1));
dbgln_if(WEBP_DEBUG, "update_mb_segmentation_map {} update_segment_feature_data {}",
segmentation.update_metablock_segmentation_map, update_segment_feature_data);
segmentation.update_macroblock_segmentation_map, update_segment_feature_data);
if (update_segment_feature_data) {
segmentation.segment_feature_mode = static_cast<SegmentFeatureMode>(TRY(L(1)));
@ -286,7 +286,7 @@ ErrorOr<Segmentation> decode_VP8_frame_header_segmentation(BooleanDecoder& decod
}
}
if (segmentation.update_metablock_segmentation_map) {
if (segmentation.update_macroblock_segmentation_map) {
// This reads mb_segment_tree_probs for https://datatracker.ietf.org/doc/html/rfc6386#section-10.
for (int i = 0; i < 3; ++i) {
u8 segment_prob_update = TRY(L(1));
@ -294,7 +294,7 @@ ErrorOr<Segmentation> decode_VP8_frame_header_segmentation(BooleanDecoder& decod
if (segment_prob_update) {
u8 segment_prob = TRY(L(8));
dbgln_if(WEBP_DEBUG, "segment_prob {}", segment_prob);
segmentation.metablock_segment_tree_probabilities[i] = segment_prob;
segmentation.macroblock_segment_tree_probabilities[i] = segment_prob;
}
}
}
@ -407,8 +407,8 @@ struct MacroblockMetadata {
// https://datatracker.ietf.org/doc/html/rfc6386#section-11.1 "mb_skip_coeff"
bool skip_coefficients { false };
IntraMetablockMode intra_y_mode;
IntraMetablockMode uv_mode;
IntraMacroblockMode intra_y_mode;
IntraMacroblockMode uv_mode;
IntraBlockMode intra_b_modes[16];
};
@ -446,14 +446,14 @@ ErrorOr<Vector<MacroblockMetadata>> decode_VP8_macroblock_metadata(BooleanDecode
for (int mb_x = 0; mb_x < macroblock_width; ++mb_x) {
MacroblockMetadata metadata;
if (header.segmentation.update_metablock_segmentation_map)
metadata.segment_id = TRY(tree_decode(decoder, METABLOCK_SEGMENT_TREE, header.segmentation.metablock_segment_tree_probabilities));
if (header.segmentation.update_macroblock_segmentation_map)
metadata.segment_id = TRY(tree_decode(decoder, MACROBLOCK_SEGMENT_TREE, header.segmentation.macroblock_segment_tree_probabilities));
if (header.enable_skipping_of_metablocks_containing_only_zero_coefficients)
if (header.enable_skipping_of_macroblocks_containing_only_zero_coefficients)
metadata.skip_coefficients = TRY(B(header.probability_skip_false));
int intra_y_mode = TRY(tree_decode(decoder, KEYFRAME_YMODE_TREE, KEYFRAME_YMODE_PROBABILITIES));
metadata.intra_y_mode = (IntraMetablockMode)intra_y_mode;
metadata.intra_y_mode = (IntraMacroblockMode)intra_y_mode;
// "If the Ymode is B_PRED, it is followed by a (tree-coded) mode for each of the 16 Y subblocks."
if (intra_y_mode == B_PRED) {
@ -482,7 +482,7 @@ ErrorOr<Vector<MacroblockMetadata>> decode_VP8_macroblock_metadata(BooleanDecode
}
}
metadata.uv_mode = (IntraMetablockMode)TRY(tree_decode(decoder, UV_MODE_TREE, KEYFRAME_UV_MODE_PROBABILITIES));
metadata.uv_mode = (IntraMacroblockMode)TRY(tree_decode(decoder, UV_MODE_TREE, KEYFRAME_UV_MODE_PROBABILITIES));
TRY(macroblock_metadata.try_append(metadata));
}

4
Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossyTables.h
View file

@ -14,7 +14,7 @@ using Prob = u8;
using TreeIndex = i8;
// https://datatracker.ietf.org/doc/html/rfc6386#section-10 "Segment-Based Feature Adjustments"
const TreeIndex METABLOCK_SEGMENT_TREE[2 * (4 - 1)] = {
const TreeIndex MACROBLOCK_SEGMENT_TREE[2 * (4 - 1)] = {
2, 4, /* root: "0", "1" subtrees */
-0, -1, /* "00" = 0th value, "01" = 1st value */
-2, -3 /* "10" = 2nd value, "11" = 3rd value */
@ -22,7 +22,7 @@ const TreeIndex METABLOCK_SEGMENT_TREE[2 * (4 - 1)] = {
// https://datatracker.ietf.org/doc/html/rfc6386#section-8.2 "Tree Coding Example"
// Repeated in https://datatracker.ietf.org/doc/html/rfc6386#section-11.2 "Luma Modes"
enum IntraMetablockMode {
enum IntraMacroblockMode {
DC_PRED, /* predict DC using row above and column to the left */
V_PRED, /* predict rows using row above */
H_PRED, /* predict columns using column to the left */