Use ICC profiles for colors (#48)

NOTICE

@@ -1,3 +1,126 @@
+================================================================================
+The Creative Commons Zero v1.0 Universal License applies to:
+* The ICC profiles found in `crates/svg2pdf/src/icc/*`
+
+================================================================================
+
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crates/svg2pdf/Cargo.toml

@@ -22,6 +22,7 @@ miniz_oxide = "0.7"
 pdf-writer = "0.9"
 usvg = { version = "0.36", default-features = false }
 image = { version = "0.24", default-features = false, features = ["jpeg", "png", "gif"], optional = true }
+once_cell = "1.18.0"
 
 [dev-dependencies]
 usvg = { version = "0.36.0" }

crates/svg2pdf/src/lib.rs

@@ -46,13 +46,20 @@ Among the unsupported features are currently:
 mod render;
 mod util;
 
+use once_cell::sync::Lazy;
 use pdf_writer::{Chunk, Content, Filter, Finish, Pdf, Rect, Ref, TextStr};
 use usvg::utils::view_box_to_transform;
 use usvg::{Align, AspectRatio, NonZeroRect, Size, Transform, Tree, TreeParsing};
 
 use crate::render::tree_to_stream;
 use crate::util::context::Context;
-use crate::util::helper::dpi_ratio;
+use crate::util::helper::{deflate, dpi_ratio};
+
+// The ICC profiles.
+static SRGB_ICC_DEFLATED: Lazy<Vec<u8>> =
+    Lazy::new(|| deflate(include_bytes!("icc/sRGB-v4.icc")));
+static GRAY_ICC_DEFLATED: Lazy<Vec<u8>> =
+    Lazy::new(|| deflate(include_bytes!("icc/sGrey-v4.icc")));
 
 /// Set size and scaling preferences for the conversion.
 #[derive(Copy, Clone)]
@@ -201,10 +208,12 @@ pub fn convert_tree(tree: &Tree, options: Options) -> Vec<u8> {
         .isolated(true)
         .knockout(false)
         .color_space()
-        .srgb();
+        .icc_based(ctx.deferrer.srgb_ref());
     page.contents(content_ref);
     page.finish();
 
+    write_color_spaces(&mut ctx, &mut pdf);
+
     let document_info_id = ctx.alloc_ref();
     pdf.document_info(document_info_id).producer(TextStr("svg2pdf"));
 
@@ -341,9 +350,32 @@ pub fn convert_tree_into(
     let mut resources = x_object.resources();
     ctx.deferrer.pop(&mut resources);
 
+    resources.finish();
+    x_object.finish();
+
+    write_color_spaces(&mut ctx, chunk);
+
     ctx.alloc_ref()
 }
 
+fn write_color_spaces(ctx: &mut Context, chunk: &mut Chunk) {
+    if ctx.deferrer.used_srgb() {
+        chunk
+            .icc_profile(ctx.deferrer.srgb_ref(), &SRGB_ICC_DEFLATED)
+            .n(3)
+            .range([0.0, 1.0, 0.0, 1.0, 0.0, 1.0])
+            .filter(Filter::FlateDecode);
+    }
+
+    if ctx.deferrer.used_sgray() {
+        chunk
+            .icc_profile(ctx.deferrer.sgray_ref(), &GRAY_ICC_DEFLATED)
+            .n(1)
+            .range([0.0, 1.0])
+            .filter(Filter::FlateDecode);
+    }
+}
+
 /// Return the dimensions of the PDF page
 fn pdf_size(tree: &Tree, options: Options) -> Size {
     // If no custom viewport is defined, we use the size of the tree.

crates/svg2pdf/src/render/clip_path.rs

@@ -192,7 +192,7 @@ fn create_complex_clip_path(
         .isolated(false)
         .knockout(false)
         .color_space()
-        .srgb();
+        .icc_based(ctx.deferrer.srgb_ref());
 
     x_object.bbox(pdf_bbox);
     x_object.finish();

crates/svg2pdf/src/render/gradient.rs

@@ -135,7 +135,7 @@ fn shading_soft_mask(
         .isolated(false)
         .knockout(false)
         .color_space()
-        .d65_gray();
+        .icc_based(ctx.deferrer.sgray_ref());
 
     if ctx.options.compress {
         x_object.filter(Filter::FlateDecode);
@@ -166,9 +166,9 @@ fn shading_function(
     let mut shading = chunk.function_shading(shading_ref);
     shading.shading_type(properties.shading_type);
     if use_opacities {
-        shading.color_space().d65_gray();
+        shading.color_space().icc_based(ctx.deferrer.sgray_ref());
     } else {
-        shading.color_space().srgb();
+        shading.color_space().icc_based(ctx.deferrer.srgb_ref());
     }
 
     shading.function(function_ref);

crates/svg2pdf/src/render/group.rs

@@ -78,7 +78,7 @@ fn create_x_object(
         .isolated(group.is_isolated())
         .knockout(false)
         .color_space()
-        .srgb();
+        .icc_based(ctx.deferrer.srgb_ref());
 
     x_object.bbox(pdf_bbox);
     x_object.finish();

crates/svg2pdf/src/render/mask.rs

@@ -87,7 +87,7 @@ pub fn create(
         .isolated(false)
         .knockout(false)
         .color_space()
-        .srgb();
+        .icc_based(ctx.deferrer.srgb_ref());
 
     x_object.bbox(actual_rect.to_pdf_rect());
     x_object.finish();

crates/svg2pdf/src/render/path.rs

@@ -8,9 +8,10 @@ use usvg::{Stroke, Transform};
 
 use super::{gradient, pattern};
 use crate::util::context::Context;
+use crate::util::defer::SRGB;
 use crate::util::helper::{
     plain_bbox, plain_bbox_without_default, ColorExt, LineCapExt, LineJoinExt, NameExt,
-    TransformExt, SRGB,
+    TransformExt,
 };
 
 /// Render a path into a content stream.

crates/svg2pdf/src/util/defer.rs

@@ -15,10 +15,12 @@ use std::rc::Rc;
 
 use pdf_writer::types::ProcSet;
 use pdf_writer::writers::{ColorSpace, Resources};
-use pdf_writer::{Dict, Finish, Ref};
+use pdf_writer::{Dict, Finish, Name, Ref};
 
 use super::allocate::Allocator;
-use super::helper::{NameExt, SRGB};
+use super::helper::NameExt;
+
+pub const SRGB: Name = Name(b"srgb");
 
 #[derive(Clone, Copy, Eq, PartialEq)]
 enum PendingResourceType {
@@ -72,6 +74,10 @@ pub struct Deferrer {
     allocator: Allocator,
     /// The stack frames containing the deferred objects.
     pending_entries: Vec<Vec<PendingResource>>,
+    /// The reference to the icc profile for srgb.
+    srgb_ref: Option<Ref>,
+    // The reference to the icc profile for sgray
+    sgray_ref: Option<Ref>,
 }
 
 impl Deferrer {
@@ -95,14 +101,39 @@ impl Deferrer {
         self.allocator.alloc_ref()
     }
 
+    pub fn used_srgb(&self) -> bool {
+        self.srgb_ref.is_some()
+    }
+
+    pub fn used_sgray(&self) -> bool {
+        self.sgray_ref.is_some()
+    }
+
+    pub fn srgb_ref(&mut self) -> Ref {
+        let allocator = &mut self.allocator;
+        *self.srgb_ref.get_or_insert_with(|| allocator.alloc_ref())
+    }
+
+    pub fn sgray_ref(&mut self) -> Ref {
+        let allocator = &mut self.allocator;
+        *self.sgray_ref.get_or_insert_with(|| allocator.alloc_ref())
+    }
+
     /// Push a new stack frame.
     pub fn push(&mut self) {
         self.pending_entries.push(Vec::new());
     }
 
     /// Pop a stack frame and write the pending named resources into the `Resources` dictionary.
     pub fn pop(&mut self, resources: &mut Resources) {
-        resources.color_spaces().insert(SRGB).start::<ColorSpace>().srgb();
+        let mut color_spaces = resources.color_spaces();
+        color_spaces
+            .insert(SRGB)
+            .start::<ColorSpace>()
+            .icc_based(self.srgb_ref());
+        // SGRAY is currently only used for soft masks with alpha, so we never need to write
+        // it into the resources directly.
+        color_spaces.finish();
         resources.proc_sets([ProcSet::Pdf, ProcSet::ImageColor, ProcSet::ImageGrayscale]);
 
         let entries = self.pending_entries.pop().unwrap();

crates/svg2pdf/src/util/helper.rs

@@ -6,8 +6,6 @@ use usvg::{
 
 use crate::render::gradient::Stop;
 
-pub const SRGB: Name = Name(b"srgb");
-
 /// Extension trait to convert [Colors](usvg::Color) into PDF colors.
 pub trait ColorExt {
     fn to_pdf_color(&self) -> [f32; 3];