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Wrong color encoding in PDF gradients #4422

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EpicEricEE opened this issue Jun 20, 2024 · 2 comments
Closed
1 task done

Wrong color encoding in PDF gradients #4422

EpicEricEE opened this issue Jun 20, 2024 · 2 comments
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bug Something isn't working pdf Related to PDF export visualize Related to drawing and visualizations.

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@EpicEricEE
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Description

Gradients using the CMYK color space don't produce the same results in PDF as in the webapp preview. The behaviour is also dependent on the viewer or printer.

Example Code 
#rect(fill: cmyk(red))

#rect(fill: gradient.linear(
  cmyk(red),
  cmyk(red).darken(70%),
  space: cmyk
))

#rect(fill: gradient.linear(
  cmyk(red),
  cmyk(red).darken(100%),
  space: cmyk
))

#rect(fill: gradient.linear(
  red,
  red.darken(70%),
  space: cmyk
))

#rect(fill: gradient.linear(
  red,
  red.darken(100%),
  space: cmyk
))

#rect(fill: gradient.linear(
  red,
  blue,
  space: cmyk
))
Webapp Chrome Edge vscode-pdf
image image image image

Reproduction URL

No response

Operating system

Web app, Windows

Typst version

  • I am using the latest version of Typst
@EpicEricEE EpicEricEE added the bug Something isn't working label Jun 20, 2024
@EpicEricEE
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The problem seems to be that only the first three components are stored for each color in the shading function as we assume that the last component is always the alpha value, but in CMYK it's the black value:

typst/crates/typst-pdf/src/color.rs

Lines 391 to 400 in a2c9807

fn convert<U: QuantizedColor>(self, color: Color) -> [U; 3] {
let range = self.range();
let [x, y, z, _] = self.encode(color);
[
U::quantize(x, [range[0], range[1]]),
U::quantize(y, [range[2], range[3]]),
U::quantize(z, [range[4], range[5]]),
]
}

If I manually add a fourth component in the PDF file, the gradients look more correct (and show up in edge).

@laurmaedje laurmaedje added pdf Related to PDF export visualize Related to drawing and visualizations. labels Jun 21, 2024
@EpicEricEE
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I just found out that a very similar issue also affects luma gradients. The colors are also stored with three components (where all are the same)

<<
  /FunctionType 2
  /Range [0 1 0 1 0 1]  <--- /Range [0 1]
  /C0 [0 0 0]           <--- /C0 [0]
  /C1 [1 1 1]           <--- /C1 [1]
  /Domain [0 1]
  /N 1
>>

but the D65Gray color space seems to only expect a single component, making Edge (and I suppose Adobe Acrobat) fail to render the gradient. When removing the additional numbers from /C0, /C1 and /Range, it works as expected.

@EpicEricEE EpicEricEE changed the title CMYK gradient issues with PDF Wrong color encoding in PDF gradients Jul 16, 2024
@FlorentCLMichel FlorentCLMichel mentioned this issue Jul 16, 2024
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@EpicEricEE @laurmaedje