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Expand grayscale JPEGs to RGB(A)

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And handle grayscale jpeg example file in test suite.
This commit is contained in:
Jeroen van Rijn
2025-09-09 17:13:21 +02:00
parent 7b3ca701e0
commit 572b26a846
4 changed files with 35 additions and 10 deletions
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core/image/jpeg/jpeg.odin
+24 -10
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@@ -190,6 +190,10 @@ load_from_context :: proc(ctx: ^$C, options := Options{}, allocator := context.a
options -= {.return_header}
}
if .do_not_expand_channels in options || .do_not_expand_grayscale in options {
return img, .Unsupported_Option
}
first := compress.read_u8(ctx) or_return
soi := cast(image.JPEG_Marker)compress.read_u8(ctx) or_return
if first != 0xFF && soi != .SOI {
@@ -941,16 +945,25 @@ load_from_context :: proc(ctx: ^$C, options := Options{}, allocator := context.a
}
}
orig_channels := img.channels
// We automatically expand grayscale images to RGB
if img.channels == 1 {
img.channels += 2
}
if .alpha_add_if_missing in options {
img.channels += 1
img.channels += 1
orig_channels += 1
}
if resize(&img.pixels.buf, img.width * img.height * img.channels) != nil {
return img, .Unable_To_Allocate_Or_Resize
}
switch img.channels {
case 1:
switch orig_channels {
case 1: // Grayscale JPEG expanded to RGB
out := mem.slice_data_cast([]image.RGB_Pixel, img.pixels.buf[:])
out_idx := 0
for y in 0..<img.height {
mcu_row := y / BLOCK_SIZE
@@ -961,13 +974,15 @@ load_from_context :: proc(ctx: ^$C, options := Options{}, allocator := context.a
mcu_idx := mcu_row * block_width + mcu_col
pixel_idx := pixel_row * BLOCK_SIZE + pixel_col
img.pixels.buf[out_idx] = cast(byte)blocks[mcu_idx][.Y][pixel_idx]
luma := cast(byte)blocks[mcu_idx][.Y][pixel_idx]
out[out_idx] = {luma, luma, luma}
out_idx += 1
}
}
case 2:
out := mem.slice_data_cast([]image.GA_Pixel, img.pixels.buf[:])
case 2: // Grayscale JPEG expanded to RGBA
out := mem.slice_data_cast([]image.RGBA_Pixel, img.pixels.buf[:])
out_idx := 0
for y in 0..<img.height {
mcu_row := y / BLOCK_SIZE
@@ -979,10 +994,8 @@ load_from_context :: proc(ctx: ^$C, options := Options{}, allocator := context.a
mcu_idx := mcu_row * block_width + mcu_col
pixel_idx := pixel_row * BLOCK_SIZE + pixel_col
out[out_idx] = {
cast(byte)blocks[mcu_idx][.Y][pixel_idx],
255, // Alpha
}
luma := cast(byte)blocks[mcu_idx][.Y][pixel_idx]
out[out_idx] = {luma, luma, luma, 255}
out_idx += 1
}
}
@@ -1034,6 +1047,7 @@ load_from_context :: proc(ctx: ^$C, options := Options{}, allocator := context.a
}
expect_EOI = true
case .TEM:
// TEM doesn't have a length, continue to next marker
case: