Only apply RemoveStridePadding() when bytes per pixel is one and fix #1183

Author: BobLd

.gitignore

@@ -249,3 +249,4 @@ _Pvt_Extensions
 
 /docs/doxygen
 /tools/UglyToad.PdfPig.ConsoleRunner/Properties/launchSettings.json
+/src/UglyToad.PdfPig.Tests/Images/Files/Pdf/indexed-png-with-mask.png

src/UglyToad.PdfPig.Tests/Images/Files/Pdf/indexed-png-with-mask.png

@@ -4,9 +4,76 @@
     using DocumentLayoutAnalysis.PageSegmenter;
     using DocumentLayoutAnalysis.WordExtractor;
     using PdfPig.Core;
+    using SkiaSharp;
 
     public class GithubIssuesTests
     {
+        [Fact]
+        public void Issue1183()
+        {
+            var path = IntegrationHelpers.GetDocumentPath("test_a.pdf");
+
+            byte[] expected =
+            [
+                82, 85, 134, 255, 87, 90, 139, 255, 81, 84, 133, 255, 87, 89, 139, 255, 89, 91, 141, 255, 81, 83, 133,
+                255, 84, 86, 136, 255, 84, 86, 136, 255, 70, 59, 113, 255, 69, 62, 116, 255, 75, 73, 126, 255, 45, 48,
+                100, 255, 42, 48, 99, 255, 50, 55, 107, 255, 56, 59, 111, 255, 64, 66, 118, 255, 68, 63, 118, 255, 61,
+                56, 111, 255, 70, 64, 120, 255, 67, 62, 117, 255, 61, 56, 111, 255, 68, 63, 118, 255, 68, 62, 118, 255,
+                59, 54, 109, 255, 61, 60, 117, 255, 69, 65, 122, 255, 67, 59, 116, 255, 71, 62, 118, 255, 66, 60, 115,
+                255, 47, 49, 102, 255, 40, 51, 102, 255, 35, 51, 100, 255, 70, 58, 114, 255, 68, 56, 112, 255, 76, 65,
+                121, 255, 68, 58, 114, 255, 66, 58, 114, 255, 71, 64, 119, 255, 62, 56, 111, 255, 67, 62, 117, 255, 77,
+                61, 118, 255, 71, 56, 113, 255, 76, 63, 119, 255, 74, 63, 118, 255, 63, 55, 108, 255, 71, 64, 116, 255,
+                73, 68, 119, 255, 52, 49, 99, 255, 38, 51, 99, 255, 49, 62, 110, 255, 39, 51, 100, 255, 46, 55, 106,
+                255, 50, 55, 107, 255, 63, 62, 116, 255, 67, 60, 116, 255, 71, 60, 116, 255, 67, 58, 112, 255, 68, 61,
+                114, 255, 70, 67, 119, 255, 50, 50, 101, 255, 42, 47, 96, 255, 49, 59, 106, 255, 40, 54, 100, 255, 42,
+                57, 103, 255, 51, 51, 102, 255, 67, 60, 112, 255, 73, 62, 114, 255, 71, 65, 117, 255, 48, 53, 103, 255,
+                45, 55, 104, 255, 49, 55, 105, 255, 63, 63, 114, 255, 68, 59, 115, 255, 71, 59, 115, 255, 73, 59, 115,
+                255, 74, 61, 118, 255, 66, 58, 114, 255, 50, 51, 105, 255, 39, 51, 104, 255, 34, 52, 103, 255, 64, 60,
+                116, 255, 67, 64, 119, 255, 66, 66, 120, 255, 46, 49, 102, 255, 45, 51, 102, 255, 52, 61, 111, 255, 39,
+                51, 99, 255, 41, 54, 102, 255, 42, 54, 100, 255, 43, 53, 99, 255, 47, 55, 103, 255, 51, 56, 104, 255,
+                56, 57, 108, 255, 67, 65, 117, 255, 67, 63, 116, 255, 52, 47, 100, 255, 44, 55, 106, 255, 44, 56, 106,
+                255, 42, 54, 103, 255, 42, 54, 102, 255, 40, 52, 100, 255, 41, 52, 99, 255, 45, 57, 103, 255, 42, 53,
+                99, 255, 38, 54, 95, 255, 39, 55, 97, 255, 47, 64, 105, 255, 37, 53, 95, 255, 37, 53, 95, 255, 46, 63,
+                104, 255, 39, 55, 96, 255, 42, 58, 99, 255, 41, 55, 105, 255, 45, 55, 106, 255, 46, 51, 103, 255, 51,
+                51, 103, 255, 63, 61, 114, 255, 70, 68, 121, 255, 60, 60, 113, 255, 46, 48, 100, 255, 49, 51, 101, 255,
+                51, 52, 103, 255, 58, 58, 109, 255, 69, 66, 119, 255, 64, 60, 113, 255, 61, 55, 109, 255, 70, 62, 118,
+                255, 67, 58, 114, 255, 72, 59, 115, 255, 70, 58, 115, 255, 72, 62, 118, 255, 61, 55, 110, 255, 64, 62,
+                116, 255, 65, 65, 119, 255, 47, 50, 104, 255, 52, 56, 109, 255, 39, 53, 106, 255, 41, 54, 107, 255, 40,
+                50, 102, 255, 45, 51, 103, 255, 64, 66, 117, 255, 62, 61, 112, 255, 67, 63, 114, 255, 53, 47, 98, 255,
+                49, 54, 101, 255, 51, 56, 104, 255, 43, 48, 95, 255, 50, 55, 102, 255, 49, 54, 102, 255, 42, 47, 94,
+                255, 51, 56, 103, 255, 47, 52, 100, 255, 72, 62, 114, 255, 71, 62, 114, 255, 72, 67, 119, 255, 52, 52,
+                103, 255, 44, 48, 99, 255, 48, 57, 106, 255, 39, 52, 100, 255, 43, 58, 106, 255, 43, 51, 98, 255, 44,
+                52, 99, 255, 48, 57, 104, 255, 46, 55, 102, 255, 41, 50, 97, 255, 45, 55, 101, 255, 49, 59, 105, 255,
+                43, 53, 100, 255, 51, 57, 106, 255, 41, 49, 98, 255, 40, 52, 100, 255, 45, 60, 107, 255, 38, 53, 101,
+                255, 36, 48, 96, 255, 46, 54, 102, 255, 49, 55, 104, 255, 44, 55, 104, 255, 46, 56, 105, 255, 48, 58,
+                107, 255, 41, 49, 99, 255, 43, 50, 100, 255, 52, 59, 108, 255, 50, 55, 105, 255, 50, 55, 105, 255, 43,
+                54, 105, 255, 42, 51, 102, 255, 45, 53, 104, 255, 45, 49, 101, 255, 63, 63, 116, 255, 66, 63, 116, 255,
+                68, 63, 117, 255, 62, 55, 109, 255, 74, 60, 120, 255, 73, 59, 119, 255, 72, 58, 119, 255, 76, 62, 122,
+                255, 74, 60, 120, 255, 71, 57, 118, 255, 75, 61, 121, 255, 76, 62, 123, 255
+            ];
+
+            using (var document = PdfDocument.Open(path, new ParsingOptions() { UseLenientParsing = true }))
+            {
+                var page = document.GetPage(16);
+                var images = page.GetImages().ToArray();
+                
+                Assert.Single(images);
+
+                var image = images[0];
+                
+                Assert.True(image.TryGetPng(out var bytes));
+
+                File.WriteAllBytes("test_a_16.png", bytes);
+
+                using (SKBitmap actual = SKBitmap.Decode(bytes, new SKImageInfo(431, 690, SKColorType.Bgra8888)))
+                {
+                    var pixels = actual.GetPixelSpan();
+                    Assert.Equal(1189560, pixels.Length);
+                    Assert.Equal(expected, pixels.Slice(0, 4 * 200).ToArray());
+                }
+            }
+        }
+
         [Fact]
         public void Issue1156()
         {

src/UglyToad.PdfPig.Tests/Integration/GithubIssuesTests.cs

@@ -39,7 +39,16 @@ public static Span<byte> Convert(ColorSpaceDetails details, Span<byte> decoded,
             var strideWidth = decoded.Length / imageHeight / bytesPerPixel;
             if (strideWidth != imageWidth)
             {
-                decoded = RemoveStridePadding(decoded, strideWidth, imageWidth, imageHeight, bytesPerPixel);
+                if (bytesPerPixel > 1)
+                {
+                    // Fixed thanks to / see discussion at https://github.com/UglyToad/PdfPig/issues/1183
+                    // Unclear what should be done here, we assume we can just remove the trailing bytes
+                    decoded = decoded.Slice(0, imageWidth * imageHeight * bytesPerPixel);
+                }
+                else
+                {
+                    decoded = RemoveStridePadding(decoded, strideWidth, imageWidth, imageHeight, bytesPerPixel);
+                }
             }
 
             return details.Transform(decoded);