From 45e405982a820c3fb81c11b65350ca7cae2a53e4 Mon Sep 17 00:00:00 2001 From: Nils Dagsson Moskopp Date: Mon, 16 May 2022 18:41:19 +0200 Subject: [PATCH] Allow encoding with A1R5G5B5 colormap --- examples.lua | 4 +++- init.lua | 60 ++++++++++++++++++++++++++++++++++++++++------------ 2 files changed, 49 insertions(+), 15 deletions(-) diff --git a/examples.lua b/examples.lua index f80663d0e..9ac530cbf 100644 --- a/examples.lua +++ b/examples.lua @@ -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"}) diff --git a/init.lua b/init.lua index bfe049166..f77b93a07 100644 --- a/init.lua +++ b/init.lua @@ -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: + -- + 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 @@ -130,10 +154,18 @@ function image:encode_data(properties) self:encode_data_R8G8B8_as_Y8_raw() end elseif "A1R5G5B5" == color_format then - if "RAW" == compression then - self:encode_data_R8G8B8_as_A1R5G5B5_raw() - elseif "RLE" == compression then - self:encode_data_R8G8B8_as_A1R5G5B5_rle() + 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