Ensure profile-less CMYK roundtrip skips space conv #3620

docs/changelog.md

@@ -20,6 +20,9 @@ Requires libvips v8.14.2
   [#3615](https://github.com/lovell/sharp/pull/3615)
   [@TomWis97](https://github.com/TomWis97)
 
+* Ensure profile-less CMYK to CMYK roundtrip skips colourspace conversion.
+  [#3620](https://github.com/lovell/sharp/issues/3620)
+
 ### v0.32.0 - 24th March 2023
 
 * Default to using sequential rather than random access read where possible.

src/pipeline.cc

@@ -322,7 +322,10 @@ class PipelineWorker : public Napi::AsyncWorker {
         } catch(...) {
           sharp::VipsWarningCallback(nullptr, G_LOG_LEVEL_WARNING, "Invalid embedded profile", nullptr);
         }
-      } else if (image.interpretation() == VIPS_INTERPRETATION_CMYK) {
+      } else if (
+        image.interpretation() == VIPS_INTERPRETATION_CMYK &&
+        baton->colourspaceInput != VIPS_INTERPRETATION_CMYK
+      ) {
         image = image.icc_transform(processingProfile, VImage::option()
           ->set("input_profile", "cmyk")
           ->set("intent", VIPS_INTENT_PERCEPTUAL));

test/unit/colourspace.js

@@ -93,6 +93,19 @@ describe('Colour space conversion', function () {
       });
   });
 
+  it('Profile-less CMYK roundtrip', async () => {
+    const [c, m, y, k] = await sharp(fixtures.inputJpgWithCmykNoProfile)
+      .pipelineColourspace('cmyk')
+      .toColourspace('cmyk')
+      .raw()
+      .toBuffer();
+
+    assert.deepStrictEqual(
+      { c, m, y, k },
+      { c: 55, m: 27, y: 0, k: 0 }
+    );
+  });
+
   it('From sRGB with RGB16 pipeline, resize with gamma, to sRGB', function (done) {
     sharp(fixtures.inputPngGradients)
       .pipelineColourspace('rgb16')