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LibGfx/JBIG2+jbig2-from-json+Tests: Implement halftone "match_image" feature, add more halftone tests #26399

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merged 6 commits into from
Nov 15, 2025
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LibGfx/JBIG2+jbig2-from-json+Tests: Implement halftone "match_image" feature, add more halftone tests #26399

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89e39f7
jbig2-from-json: Update outdated diagnostic messages
nico Nov 14, 2025
3144b46
jbig2-from-json: Extract jbig2_bitmap_from_json()
nico Nov 14, 2025
9fa696f
jbig2-from-json: Delay construction of HalftoneRegionSegmentData
nico Nov 14, 2025
5e88558
LibGfx/JBIG2+jbig2-from-json: Implement halftone "match_image" feature
nico Nov 14, 2025
66cf60b
Tests/LibGfx: Add JBIG2 halftone test using match_image
nico Nov 14, 2025
4d48ca2
Tests/LibGfx: Add JBIG2 halftone tests for templates 1-3
nico Nov 14, 2025
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49 changes: 48 additions & 1 deletion Userland/Libraries/LibGfx/ImageFormats/JBIG2Writer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1987,7 +1987,54 @@ static ErrorOr<void> encode_halftone_region(JBIG2::HalftoneRegionSegmentData con
if (enable_skip)
return Error::from_string_literal("JBIG2Writer: Halftone region skip pattern not yet implemented");

GrayscaleInputParameters inputs { .grayscale_image = halftone_region.grayscale_image, .skip_pattern = skip_pattern };
Vector<u64> grayscale_image = TRY(halftone_region.grayscale_image.visit(
[](Vector<u64> const& grayscale_image) -> ErrorOr<Vector<u64>> {
return grayscale_image;
},
[&halftone_region, &pattern_dictionary](NonnullRefPtr<Gfx::Bitmap> const& reference) -> ErrorOr<Vector<u64>> {
// FIXME: This does not handle rotation or non-trivial grid vectors yet.
if (halftone_region.grid_offset_x_times_256 != 0 || halftone_region.grid_offset_y_times_256 != 0)
return Error::from_string_literal("JBIG2Writer: Halftone region match_image with non-zero grid offsets not yet implemented");
if (pattern_dictionary.pattern_width != pattern_dictionary.pattern_height
|| halftone_region.grid_vector_x_times_256 / 256 != pattern_dictionary.pattern_width
|| halftone_region.grid_vector_y_times_256 != 0)
return Error::from_string_literal("JBIG2Writer: Halftone region match_image with non-trivial grid vectors not yet implemented");

Vector<u64> converted_image;
TRY(converted_image.try_resize(halftone_region.grayscale_width * halftone_region.grayscale_height));
for (u32 y = 0; y < halftone_region.grayscale_height; ++y) {
for (u32 x = 0; x < halftone_region.grayscale_width; ++x) {
// Find best tile in pattern dictionary that matches reference best.
// FIXME: This is a naive, inefficient implementation.
u32 best_pattern_index = 0;
u32 best_pattern_difference = UINT32_MAX;
for (u32 pattern_index = 0; pattern_index <= pattern_dictionary.gray_max; ++pattern_index) {
u32 pattern_x = pattern_index * pattern_dictionary.pattern_width;
u32 pattern_difference = 0;
for (u32 py = 0; py < pattern_dictionary.pattern_height; ++py) {
for (u32 px = 0; px < pattern_dictionary.pattern_width; ++px) {
Comment on lines +2005 to +2015
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@Hendiadyoin1 Hendiadyoin1 Nov 15, 2025

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casual n^5 algo?

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@nico nico Nov 15, 2025

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The halftone region is a tiling of the reference image, so the outer x/y walks the reference image in tile increments and the inner walks the tile data. So in a way this does O(number of patterns) work per pixel (to find the best pattern to match each tile). I'd call this O(n^3).

Still, as the comment says, yes, this is inefficient. (It's not super duper slow in practice though, just regular slow: I tried covering Tests/LibGfx/test-inputs/jpg/big_image.jpg, a 4000x3000 image, with 16 possible 4x4 tiles, and that took less than a second.)

int reference_x = x * pattern_dictionary.pattern_width + px;
int reference_y = y * pattern_dictionary.pattern_height + py;
if (reference_x >= reference->width() || reference_y >= reference->height())
continue;
auto pattern_pixel = pattern_dictionary.image->get_bit(pattern_x + px, py);
auto reference_pixel = reference->get_pixel(reference_x, reference_y);
pattern_difference += abs(reference_pixel.luminosity() - (pattern_pixel ? 0 : 255));
}
}
if (pattern_difference < best_pattern_difference) {
best_pattern_difference = pattern_difference;
best_pattern_index = pattern_index;
}
}
converted_image[y * halftone_region.grayscale_width + x] = best_pattern_index;
}
}

return converted_image;
}));

GrayscaleInputParameters inputs { .grayscale_image = grayscale_image, .skip_pattern = skip_pattern };
inputs.uses_mmr = halftone_region.flags & 1;
inputs.skip_pattern = skip_pattern;
inputs.bpp = bits_per_pattern;
Expand Down
11 changes: 8 additions & 3 deletions Userland/Libraries/LibGfx/ImageFormats/JBIG2Writer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -168,9 +168,14 @@ struct HalftoneRegionSegmentData {
u16 grid_vector_x_times_256 { 0 };
u16 grid_vector_y_times_256 { 0 };

// Indices into pattern dictionary. At most 64 bits set per pixel.
// grayscale_width * grayscale_height entries.
Vector<u64> grayscale_image;
Variant<
// Indices into pattern dictionary. At most 64 bits set per pixel,
// grayscale_width * grayscale_height entries,
Vector<u64>,

// Reference image, compute gray_map by matching pattern dictionary tiles to it.
NonnullRefPtr<Gfx::Bitmap>>
grayscale_image;

MQArithmeticEncoder::Trailing7FFFHandling trailing_7fff_handling { MQArithmeticEncoder::Trailing7FFFHandling::Keep };
};
Expand Down
37 changes: 27 additions & 10 deletions Userland/Utilities/jbig2-from-json.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1578,35 +1578,48 @@ static ErrorOr<u8> jbig2_halftone_region_flags_from_json(JsonObject const& objec
return flags;
}

static ErrorOr<Vector<u64>> jbig2_halftone_graymap_from_json(ToJSONOptions const&, JsonObject const& object)
static ErrorOr<Variant<Vector<u64>, NonnullRefPtr<Gfx::Bitmap>>> jbig2_halftone_graymap_from_json(ToJSONOptions const& options, JsonObject const& object)
{
Vector<u64> graymap;
Optional<Variant<Vector<u64>, NonnullRefPtr<Gfx::Bitmap>>> graymap;

TRY(object.try_for_each_member([&](StringView key, JsonValue const& value) -> ErrorOr<void> {
if (key == "array") {
if (value.is_array()) {
Vector<u64> graymap_data;
for (auto const& row : value.as_array().values()) {
if (!row.is_array())
return Error::from_string_literal("expected array for \"array\" entries");

for (auto const& element : row.as_array().values()) {
if (auto value = element.get_u64(); value.has_value()) {
TRY(graymap.try_append(value.value()));
TRY(graymap_data.try_append(value.value()));
continue;
}
return Error::from_string_literal("expected u64 for \"graymap_data\" elements");
}
}
graymap = move(graymap_data);
return {};
}
return Error::from_string_literal("expected array for \"array\"");
}

if (key == "match_image") {
if (value.is_string()) {
graymap = TRY(jbig2_bitmap_from_json(options, value.as_string()));
return {};
}
return Error::from_string_literal("expected string for \"match_image\"");
}

dbgln("graymap_data key {}", key);
return Error::from_string_literal("unknown graymap_data key");
}));

return graymap;
if (!graymap.has_value())
return Error::from_string_literal("graymap_data object must have \"array\" or \"match_image\" member");

return graymap.release_value();
}

static ErrorOr<Gfx::JBIG2::HalftoneRegionSegmentData> jbig2_halftone_region_from_json(ToJSONOptions const& options, Optional<JsonObject const&> object)
Expand All @@ -1622,8 +1635,9 @@ static ErrorOr<Gfx::JBIG2::HalftoneRegionSegmentData> jbig2_halftone_region_from
i32 grid_offset_y_times_256 { 0 };
u16 grid_vector_x_times_256 { 0 };
u16 grid_vector_y_times_256 { 0 };
Vector<u64> grayscale_image;
Optional<Variant<Vector<u64>, NonnullRefPtr<Gfx::Bitmap>>> grayscale_image;
Gfx::MQArithmeticEncoder::Trailing7FFFHandling trailing_7fff_handling { Gfx::MQArithmeticEncoder::Trailing7FFFHandling::Keep };

TRY(object->try_for_each_member([&](StringView key, JsonValue const& value) -> ErrorOr<void> {
if (key == "region_segment_information"sv) {
if (value.is_object()) {
Expand Down Expand Up @@ -1708,10 +1722,10 @@ static ErrorOr<Gfx::JBIG2::HalftoneRegionSegmentData> jbig2_halftone_region_from
}
if (value.is_string()) {
if (value.as_string() == "identity_tile_indices"sv) {
grayscale_image.clear();
u32 num_pixels = grayscale_width * grayscale_height;
for (u32 i = 0; i < num_pixels; ++i)
TRY(grayscale_image.try_append(i));
Vector<u64> graymap;
for (u32 i = 0; i < grayscale_width * grayscale_height; ++i)
TRY(graymap.try_append(i));
grayscale_image = move(graymap);
return {};
}
}
Expand All @@ -1722,6 +1736,9 @@ static ErrorOr<Gfx::JBIG2::HalftoneRegionSegmentData> jbig2_halftone_region_from
return Error::from_string_literal("unknown halftone_region key");
}));

if (!grayscale_image.has_value())
return Error::from_string_literal("halftone_region \"data\" object missing \"graymap_data\"");

return Gfx::JBIG2::HalftoneRegionSegmentData {
region_segment_information,
flags,
Expand All @@ -1731,7 +1748,7 @@ static ErrorOr<Gfx::JBIG2::HalftoneRegionSegmentData> jbig2_halftone_region_from
grid_offset_y_times_256,
grid_vector_x_times_256,
grid_vector_y_times_256,
move(grayscale_image),
grayscale_image.release_value(),
trailing_7fff_handling,
};
}
Expand Down