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Allow encoding with A1R5G5B5 colormap

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Nils Dagsson Moskopp 2022-05-16 18:41:19 +02:00
parent e83894fcfa
commit 45e405982a
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GPG key ID: A3BC671C35191080
2 changed files with 49 additions and 15 deletions
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4
examples.lua
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@ -125,4 +125,6 @@ local pixels = {
}
-- note that the uncompressed colormapped TGA file written in this
-- example is 108 bytes – but an optimized PNG file is 121 bytes …
tga_encoder.image(pixels):save("colormapped_8bpp.tga", {colormap=colormap})
tga_encoder.image(pixels):save("colormapped_B8G8R8.tga", {colormap=colormap})
-- encoding as A1R5G5B5 saves 1 byte per palette entry → 103 bytes
tga_encoder.image(pixels):save("colormapped_A1R5G5B5.tga", {colormap=colormap, color_format="A1R5G5B5"})

52
init.lua
View file

@ -14,11 +14,20 @@ function image:constructor(pixels)
self.height = #pixels
end
local pixel_depth_by_color_format = {
["Y8"] = 8,
["A1R5G5B5"] = 16,
["B8G8R8"] = 24,
["B8G8R8A8"] = 32,
}
function image:encode_colormap_spec(properties)
local colormap = properties.colormap
local colormap_pixel_depth = 0
if 0 ~= #colormap then
colormap_pixel_depth = #colormap[1] * 8
colormap_pixel_depth = pixel_depth_by_color_format[
properties.color_format
]
end
local colormap_spec =
string.char(0, 0) .. -- first entry index
@ -35,12 +44,6 @@ function image:encode_image_spec(properties)
"B8G8R8" == color_format or -- (B8G8R8 = 3 bytes = 24 bits)
"B8G8R8A8" == color_format -- (B8G8R8A8 = 4 bytes = 32 bits)
)
pixel_depth_by_color_format = {
["Y8"] = 8,
["A1R5G5B5"] = 16,
["B8G8R8"] = 24,
["B8G8R8A8"] = 32,
}
local pixel_depth
if 0 ~= #properties.colormap then
pixel_depth = self.pixel_depth
@ -62,10 +65,30 @@ function image:encode_colormap(properties)
if 0 == #colormap then
return
end
local colormap_pixel_depth = #colormap[1] * 8
assert( 24 == colormap_pixel_depth )
local color_format = properties.color_format
assert (
"A1R5G5B5" == color_format or
"B8G8R8" == color_format
)
local colors = {}
if 24 == colormap_pixel_depth then
if "A1R5G5B5" == color_format then
-- Sample depth rescaling is done according to the algorithm presented in:
-- <https://www.w3.org/TR/2003/REC-PNG-20031110/#13Sample-depth-rescaling>
local max_sample_in = math.pow(2, 8) - 1
local max_sample_out = math.pow(2, 5) - 1
for i = 1,#colormap,1 do
local color = colormap[i]
local colorword = 32768 +
((math.floor((color[1] * max_sample_out / max_sample_in) + 0.5)) * 1024) +
((math.floor((color[2] * max_sample_out / max_sample_in) + 0.5)) * 32) +
((math.floor((color[3] * max_sample_out / max_sample_in) + 0.5)) * 1)
local color_bytes = string.char(
colorword % 256,
math.floor(colorword / 256)
)
colors[#colors + 1] = color_bytes
end
elseif "B8G8R8" == color_format then
for i = 1,#colormap,1 do
local color = colormap[i]
local color_bytes = string.char(
@ -76,6 +99,7 @@ function image:encode_colormap(properties)
colors[#colors + 1] = color_bytes
end
end
assert( 0 ~= #colors )
self.data = self.data .. table.concat(colors)
end
@ -130,11 +154,19 @@ function image:encode_data(properties)
self:encode_data_R8G8B8_as_Y8_raw()
end
elseif "A1R5G5B5" == color_format then
if 0 ~= #colormap then
if "RAW" == compression then
if 8 == self.pixel_depth then
self:encode_data_Y8_as_Y8_raw()
end
end
else
if "RAW" == compression then
self:encode_data_R8G8B8_as_A1R5G5B5_raw()
elseif "RLE" == compression then
self:encode_data_R8G8B8_as_A1R5G5B5_rle()
end
end
elseif "B8G8R8" == color_format then
if 0 ~= #colormap then
if "RAW" == compression then