Merge pull request #54 from JuliaIO/nontransparent_images_with_backgr…

…ound Support opaque images with background chunks
JuliaIO · Feb 5, 2022 · 74a8cee · 74a8cee
2 parents 63701b1 + 7b7f226
commit 74a8cee
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Showing 3 changed files with 25 additions and 12 deletions.
diff --git a/src/io.jl b/src/io.jl
@@ -123,6 +123,10 @@ function _load(png_ptr, info_ptr; gamma::Union{Nothing,Float64}=nothing, expand_
     interlace_type = png_get_interlace_type(png_ptr, info_ptr)
     background_color = nothing
     is_transparent = valid_tRNS | (color_type & PNG_COLOR_MASK_ALPHA) != 0 
+    is_gray = (color_type == PNG_COLOR_TYPE_GRAY_ALPHA) | (color_type == PNG_COLOR_TYPE_GRAY)
+
+    read_as_paletted = !expand_paletted && color_type == PNG_COLOR_TYPE_PALETTE && bit_depth == 8 && valid_PLTE
+    read_with_background = _check_background_load(background, is_gray, valid_PLTE, read_as_paletted)
 
     screen_gamma = PNG_DEFAULT_sRGB
     image_gamma = Ref{Cdouble}(-1.0)
@@ -148,11 +152,6 @@ function _load(png_ptr, info_ptr; gamma::Union{Nothing,Float64}=nothing, expand_
         png_set_gamma(png_ptr, screen_gamma, image_gamma[])
     end
 
-    read_as_paletted = !expand_paletted &&
-        color_type == PNG_COLOR_TYPE_PALETTE &&
-        bit_depth == 8 && 
-        valid_PLTE
-
     if !read_as_paletted
         if color_type == PNG_COLOR_TYPE_PALETTE
             png_set_palette_to_rgb(png_ptr)
@@ -172,7 +171,7 @@ function _load(png_ptr, info_ptr; gamma::Union{Nothing,Float64}=nothing, expand_
             end
         end
 
-        if valid_bKGD & ((color_type | PNG_COLOR_MASK_ALPHA) > 0)
+        if read_with_background & valid_bKGD & is_transparent
             png_set_filler(png_ptr, 0xff, PNG_FILLER_AFTER)
         end
         buffer_eltype = _buffer_color_type(color_type, bit_depth)
@@ -182,10 +181,9 @@ function _load(png_ptr, info_ptr; gamma::Union{Nothing,Float64}=nothing, expand_
         buffer_eltype = UInt8
     end
 
-    is_gray = (color_type == PNG_COLOR_TYPE_GRAY_ALPHA) | (color_type == PNG_COLOR_TYPE_GRAY)
-    if _check_background_load(background, is_gray, valid_PLTE, read_as_paletted)
-        is_transparent || throw(ArgumentError("Only transparent images can have a background"))
+    if read_with_background
         background_color = process_background(png_ptr, info_ptr, _adjust_background_bitdepth(background, bit_depth))
+        is_transparent || @warn("Background color for non-transparent image: $(background_color)")
     end
 
     n_passes = png_set_interlace_handling(png_ptr)
@@ -468,7 +466,6 @@ function _save(png_ptr, info_ptr, image::S;
         end
     end
     if !(background === nothing)
-        is_transparent || throw(ArgumentError("Only transparent images can have a background"))
         _check_background_save(background, color_type)
         _png_set_bKGD(png_ptr, info_ptr, _adjust_background_bitdepth(background, bit_depth))
     end

diff --git a/test/test_images/nontransparent_image_with_background.png b/test/test_images/nontransparent_image_with_background.png
diff --git a/test/test_invalid_inputs.jl b/test/test_invalid_inputs.jl
@@ -16,8 +16,11 @@ incompatible_background_arguments = [
     ("graya_img_rgb_background", ArgumentError, rand(127, 257, 2), "temp/PngSuite/bgbn4a08.png", RGB{N0f8}(1.0, 0.5, 0.0)),
     ("graya_img_index_background", ArgumentError, rand(127, 257, 2), "temp/PngSuite/bgbn4a08.png", 0x00),
     ("rgba_img_index_background", ArgumentError, rand(127, 257, 4), "temp/PngSuite/bgwn6a08.png", 0x00),
-    ("rgb_no_alpha_background", ArgumentError, rand(127, 257, 3), "temp/PngSuite/basn2c08.png", RGB{N0f8}(0.0)),
-    ("gray_no_alpha_background", ArgumentError, rand(127, 257, 1), "temp/PngSuite/basn0g08.png", Gray{N0f8}(1.0)),
+]
+
+warn_background_arguments = [
+    ("rgb_no_alpha_background", rand(127, 257, 3), "temp/PngSuite/basn2c08.png", RGB{N0f8}(0.0)),
+    ("gray_no_alpha_background", rand(127, 257, 1), "temp/PngSuite/basn0g08.png", Gray{N0f8}(0.0)),
 ]
 
 @testset "Invalid inputs" begin
@@ -53,4 +56,17 @@ incompatible_background_arguments = [
             @test_throws ArgumentError PNGFiles.load("test_images/paletted_implicit_transparency.png", background=0x00)
         end
     end
+
+    warn_msg = "Background color for non-transparent image: PNGFiles._png_color_16_struct(0x00, 0x0000, 0x0000, 0x0000, 0x0000)"
+    for (case, image, load_path, bg) in warn_background_arguments
+        @testset "$(case) throws save" begin
+            @test PNGFiles.save(joinpath(PNG_TEST_PATH, "test_img_err_$(case).png"), image, background=bg) === nothing
+        end
+        @testset "$(case) throws load" begin
+            @test_logs (:warn, warn_msg) PNGFiles.load(load_path, background=bg)
+        end
+    end
+    @testset "non_transparent_image_with_background_warns" begin
+        @test_throws ArgumentError PNGFiles.load("test_images/nontransparent_image_with_background.png", background=0x00)
+    end
 end