Docs: state the stop limit for Perceptual spot gradient shadings

PDF export writes a Perceptual spot gradient as a Separation or DeviceN shading only when its expanded curve has at most 4,096 stops (MAX_INK_TINTS in crates/color/src/gradient.rs). Longer curves are written as images, with the process-color warning.
2026-11-11 02:19:56 -06:00 · 2026-11-04 14:56:35 +07:00
parent d977fd9181
commit b9d3881872
1 changed files with 1 additions and 1 deletions
@@ -1369,7 +1369,7 @@ applies to fills). Tests: `color::gradient::tests` (perceptual midpoint, expansi
 `pdf::tests::dithered_perceptual_gradients_export_as_images_with_noise_on_the_fill` and the Gradient panel's
 `the_method_menu_makes_the_gradient_perceptual`. Scores and hours unchanged.

-PDF export writes a Perceptual linear or radial gradient whose stops are tints of one spot color (and paper white) as a Separation shading in that ink instead of an image, so the ink keeps its plate ([swatches](https://helpx.adobe.com/illustrator/using/using-creating-swatches.html); [separations](https://helpx.adobe.com/illustrator/using/printing-color-separations.html)). Its tints follow the curve's stops, each the tint with the OKLab lightness of the color there (VectorCraft's own rule). A Perceptual gradient that mixes spot colors with each other or with CMYK or gray stops is written as a DeviceN shading of its inks: at each stop on the curve, the inks of the two stops on either side are mixed at the weight where the two colors mixed in display RGB have the OKLab lightness of the color there (VectorCraft's own rule). Dithered fills, freeform gradients and Perceptual gradients that mix a spot color with RGB or Lab stops are still images, and the export warns that their spot colors are written in process colors. Tests: `color::gradient::tests::ink_tints_follow_the_perceptual_curve` and `ink_mixes_follow_the_perceptual_curve`, `engine::tests::linked_stops::perceptual_spot_gradients_export_as_separation_shadings`, `perceptual_spot_gradients_mixed_with_other_inks_export_as_device_n_shadings` and `spot_gradients_drawn_as_images_warn`.
+PDF export writes a Perceptual linear or radial gradient whose stops are tints of one spot color (and paper white) as a Separation shading in that ink instead of an image, so the ink keeps its plate ([swatches](https://helpx.adobe.com/illustrator/using/using-creating-swatches.html); [separations](https://helpx.adobe.com/illustrator/using/printing-color-separations.html)). Its tints follow the curve's stops, each the tint with the OKLab lightness of the color there (VectorCraft's own rule). A Perceptual gradient that mixes spot colors with each other or with CMYK or gray stops is written as a DeviceN shading of its inks: at each stop on the curve, the inks of the two stops on either side are mixed at the weight where the two colors mixed in display RGB have the OKLab lightness of the color there (VectorCraft's own rule). Dithered fills, freeform gradients, Perceptual gradients that mix a spot color with RGB or Lab stops, and Perceptual gradients whose curve has more than 4,096 stops once expanded (VectorCraft's own limit) are still images, and the export warns that their spot colors are written in process colors. Tests: `color::gradient::tests::ink_tints_follow_the_perceptual_curve` and `ink_mixes_follow_the_perceptual_curve`, `engine::tests::linked_stops::perceptual_spot_gradients_export_as_separation_shadings`, `perceptual_spot_gradients_mixed_with_other_inks_export_as_device_n_shadings` and `spot_gradients_drawn_as_images_warn`.

 In these Separation and DeviceN shadings, a white stop linked to a swatch that is not a spot color (a global White swatch, for example) is paper white, 0% of the ink, as an unlinked white stop is, so a gradient of one spot ink and such a stop stays a Separation shading; a stop linked to a white spot color stays a stop of that ink (VectorCraft's own rule). Test: `engine::tests::linked_stops::white_stops_linked_to_process_swatches_are_paper_in_spot_gradients`.