Fix cropping grayscale JPEG images

src/Modifiers/CropModifier.php

@@ -76,16 +76,22 @@ private function background(SizeInterface $resizeTo, ImageInterface $image): Vip
             $bgColor->channel(Blue::class)->value(),
         ];
 
+        $originalImage = $image->core()->native();
+        if ($originalImage->bands === 1) {
+            // Grayscale -> RGB
+            $originalImage = $originalImage->colourspace('srgb');
+        }
+
         // original image and background must have the same number of bands
-        if ($image->core()->native()->hasAlpha()) {
+        if ($originalImage->hasAlpha()) {
             $bands[] = $bgColor->channel(Alpha::class)->value();
         }
 
         return VipsImage::black(1, 1)
             ->add($bgColor->channel(Red::class)->value())
-            ->cast($image->core()->native()->format)
+            ->cast($originalImage->format)
             ->embed(0, 0, $resizeTo->width(), $resizeTo->height(), ['extend' => Extend::COPY])
-            ->copy(['interpretation' => $image->core()->native()->interpretation])
+            ->copy(['interpretation' => $originalImage->interpretation])
             ->bandjoin($bands);
     }
 

tests/Unit/Modifiers/CropModifierTest.php

@@ -88,4 +88,16 @@ public function testModifyCropAnimatedSmart(): void
         $this->assertEquals(15, $image->height());
         $this->assertColor(255, 166, 1, 255, $image->pickColor(8, 8));
     }
+
+    public function testCropGrayscale(): void
+    {
+        $image = $this->readTestImage('grayscale.jpg');
+        $image->modify(new CropModifier(258, 258, 0, 0, 'ff0000', 'center'));
+        $this->assertColor(255, 0, 0, 255, $image->pickColor(0, 0));
+        $this->assertColor(255, 255, 255, 255, $image->pickColor(1, 1));
+        $this->assertColor(0, 0, 0, 255, $image->pickColor(1, 256));
+
+        // Ensure the image is encodable
+        $image->encode();
+    }
 }