Remove decode parameter application from Stencil color space for consistency

Author: BobLd

src/UglyToad.PdfPig.Tests/Images/PngFromPdfImageFactoryTests.cs

@@ -172,11 +172,12 @@ public void CanGeneratePngFromCcittFaxDecodedImageData()
             var decodedBytes = ImageHelpers.LoadFileBytes("ccittfax-decoded.bin");
             var image = new TestPdfImage
             {
-                ColorSpaceDetails = IndexedColorSpaceDetails.Stencil(DeviceGrayColorSpaceDetails.Instance, new[] { 1.0, 0 }),
+                ColorSpaceDetails = IndexedColorSpaceDetails.Stencil(DeviceGrayColorSpaceDetails.Instance),
                 DecodedBytes = decodedBytes,
                 WidthInSamples = 1800,
                 HeightInSamples = 3113,
-                BitsPerComponent = 1
+                BitsPerComponent = 1,
+                Decode = [1.0, 0]
             };
 
             Assert.True(PngFromPdfImageFactory.TryGenerate(image, out var bytes));

src/UglyToad.PdfPig/Content/PdfImageExtensions.cs

@@ -10,13 +10,7 @@ public static class PdfImageExtensions
         /// </summary>
         public static bool NeedsReverseDecode(this IPdfImage pdfImage)
         {
-            if (pdfImage.ColorSpaceDetails?.IsStencil == true)
-            {
-                // Stencil color space already takes care of reversing.
-                return false;
-            }
-
-            return pdfImage.Decode.Count >= 2 && pdfImage.Decode[0] == 1 && pdfImage.Decode[1] == 0;
+            return pdfImage.Decode?.Count >= 2 && pdfImage.Decode[0] == 1 && pdfImage.Decode[1] == 0;
         }
     }
 }

src/UglyToad.PdfPig/Graphics/Colors/ColorSpaceDetails.cs

@@ -15,12 +15,6 @@
     /// </summary>
     public abstract class ColorSpaceDetails
     {
-        /// <summary>
-        /// Is the color space a stencil indexed color space.
-        /// <para>Stencil color spaces take care of inverting colors based on the Decode array.</para>
-        /// </summary>
-        public bool IsStencil { get; }
-
         /// <summary>
         /// The type of the ColorSpace.
         /// </summary>
@@ -45,11 +39,10 @@ public abstract class ColorSpaceDetails
         /// <summary>
         /// Create a new <see cref="ColorSpaceDetails"/>.
         /// </summary>
-        protected internal ColorSpaceDetails(ColorSpace type, bool isStencil = false)
+        protected internal ColorSpaceDetails(ColorSpace type)
         {
             Type = type;
             BaseType = type;
-            IsStencil = isStencil;
         }
 
         /// <summary>
@@ -278,15 +271,12 @@ public sealed class IndexedColorSpaceDetails : ColorSpaceDetails
         private readonly ConcurrentDictionary<double, IColor> cache = new ConcurrentDictionary<double, IColor>();
 
         /// <summary>
-        /// Creates a indexed color space useful for extracting stencil masks as black-and-white images,
-        /// i.e. with a color palette of two colors (black and white). If the decode parameter array is
-        /// [0, 1] it indicates that black is at index 0 in the color palette, whereas [1, 0] indicates
-        /// that the black color is at index 1.
+        /// Creates an indexed color space useful for extracting stencil masks as black-and-white images,
+        /// i.e. with a color palette of two colors (black and white).
         /// </summary>
-        internal static ColorSpaceDetails Stencil(ColorSpaceDetails colorSpaceDetails, double[] decode)
+        internal static ColorSpaceDetails Stencil(ColorSpaceDetails colorSpaceDetails)
         {
-            var blackIsOne = decode.Length >= 2 && decode[0] == 1 && decode[1] == 0;
-            return new IndexedColorSpaceDetails(colorSpaceDetails, 1, blackIsOne ? [255, 0] : [0, 255], true);
+            return new IndexedColorSpaceDetails(colorSpaceDetails, 1, [0, 255]);
         }
 
         /// <inheritdoc/>
@@ -321,14 +311,7 @@ internal static ColorSpaceDetails Stencil(ColorSpaceDetails colorSpaceDetails, d
         /// Create a new <see cref="IndexedColorSpaceDetails"/>.
         /// </summary>
         public IndexedColorSpaceDetails(ColorSpaceDetails baseColorSpaceDetails, byte hiVal, byte[] colorTable)
-            : this(baseColorSpaceDetails, hiVal, colorTable, false)
-        { }
-
-        /// <summary>
-        /// Create a new <see cref="IndexedColorSpaceDetails"/>.
-        /// </summary>
-        private IndexedColorSpaceDetails(ColorSpaceDetails baseColorSpaceDetails, byte hiVal, byte[] colorTable, bool isStencil)
-            : base(ColorSpace.Indexed, isStencil)
+            : base(ColorSpace.Indexed)
         {
             BaseColorSpace = baseColorSpaceDetails ?? throw new ArgumentNullException(nameof(baseColorSpaceDetails));
             HiVal = hiVal;

src/UglyToad.PdfPig/Images/Png/PngFromPdfImageFactory.cs

@@ -159,13 +159,28 @@ public static bool TryGenerate(IPdfImage image, [NotNullWhen(true)] out byte[]?
                 else
                 {
                     int i = 0;
-                    for (int col = 0; col < image.HeightInSamples; col++)
+                    if (!image.NeedsReverseDecode()) // TODO - Need to properly implement decode for other numberOfComponents
                     {
-                        for (int row = 0; row < image.WidthInSamples; row++)
+                        for (int col = 0; col < image.HeightInSamples; col++)
+                        {
+                            for (int row = 0; row < image.WidthInSamples; row++)
+                            {
+                                byte a = getAlphaChannel(i);
+                                byte pixel = bytesPure[i++];
+                                builder.SetPixel(new Pixel(pixel, pixel, pixel, a, false), row, col);
+                            }
+                        }
+                    }
+                    else
+                    {
+                        for (int col = 0; col < image.HeightInSamples; col++)
                         {
-                            byte a = getAlphaChannel(i);
-                            byte pixel = bytesPure[i++];
-                            builder.SetPixel(new Pixel(pixel, pixel, pixel, a, false), row, col);
+                            for (int row = 0; row < image.WidthInSamples; row++)
+                            {
+                                byte a = getAlphaChannel(i);
+                                byte pixel = (byte)(255 - bytesPure[i++]); // Inverse decode
+                                builder.SetPixel(new Pixel(pixel, pixel, pixel, a, false), row, col);
+                            }
                         }
                     }
                 }

src/UglyToad.PdfPig/Util/ColorSpaceDetailsParser.cs

@@ -54,11 +54,7 @@ public static ColorSpaceDetails GetColorSpaceDetails(ColorSpace? colorSpace,
                 }
 
                 var colorSpaceDetails = GetColorSpaceDetails(colorSpace, imageDictionary.Without(NameToken.Filter).Without(NameToken.F), scanner, resourceStore, filterProvider, true);
-
-                var decodeRaw = imageDictionary.GetObjectOrDefault(NameToken.Decode, NameToken.D) as ArrayToken ?? new ArrayToken([]);
-                var decode = decodeRaw.Data.OfType<NumericToken>().Select(static x => x.Double).ToArray();
-
-                return IndexedColorSpaceDetails.Stencil(colorSpaceDetails, decode);
+                return IndexedColorSpaceDetails.Stencil(colorSpaceDetails);
             }
 
             if (!colorSpace.HasValue)

src/UglyToad.PdfPig/XObjects/XObjectFactory.cs

@@ -92,7 +92,6 @@ public static XObjectImage ReadImage(XObjectContentRecord xObject,
                     null);
 
                 softMaskImage = ReadImage(maskImageRecord, pdfScanner, filterProvider, resourceStore);
-                System.Diagnostics.Debug.Assert(softMaskImage.ColorSpaceDetails?.IsStencil == true);
             }
 
             var isJpxDecode = dictionary.TryGet(NameToken.Filter, out NameToken filterName) && filterName.Equals(NameToken.JpxDecode);