add support for extracting grayscale images and inline images

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

@@ -0,0 +1,61 @@
+namespace UglyToad.PdfPig.Images.Png
+{
+    using Content;
+    using Graphics.Colors;
+
+    internal static class PngFromPdfImageFactory
+    {
+        public static bool TryGenerate(IPdfImage image, out byte[] bytes)
+        {
+            bytes = null;
+
+            var isColorSpaceSupported = image.ColorSpace == ColorSpace.DeviceGray || image.ColorSpace == ColorSpace.DeviceRGB;
+            if (!isColorSpaceSupported || !image.TryGetBytes(out var bytesPure))
+            {
+                return false;
+            }
+
+            try
+            {
+                var is3Byte = image.ColorSpace == ColorSpace.DeviceRGB;
+                var multiplier = is3Byte ? 3 : 1;
+
+                var builder = PngBuilder.Create(image.WidthInSamples, image.HeightInSamples, false);
+
+                var isCorrectlySized = bytesPure.Count == (image.WidthInSamples * image.HeightInSamples * (image.BitsPerComponent / 8) * multiplier);
+
+                if (!isCorrectlySized)
+                {
+                    return false;
+                }
+
+                var i = 0;
+                for (var y = 0; y < image.HeightInSamples; y++)
+                {
+                    for (var x = 0; x < image.WidthInSamples; x++)
+                    {
+                        if (is3Byte)
+                        {
+                            builder.SetPixel(bytesPure[i++], bytesPure[i++], bytesPure[i++], x, y);
+                        }
+                        else
+                        {
+                            var pixel = bytesPure[i++];
+                            builder.SetPixel(pixel, pixel, pixel, x, y);
+                        }
+                    }
+                }
+
+                bytes = builder.Save();
+
+                return true;
+            }
+            catch
+            {
+                // ignored.
+            }
+
+            return false;
+        }
+    }
+}