// Given three images, return an image that highlights the differences in common betwen the main image and the first image
// and the main image and a second image.
public static unsafe WriteableBitmap CombinedDifference(this WriteableBitmap unaltered, WriteableBitmap previous, WriteableBitmap next, byte threshold)
{
// Check the arguments for null
ThrowIf.IsNullArgument(unaltered, nameof(unaltered));
ThrowIf.IsNullArgument(previous, nameof(previous));
ThrowIf.IsNullArgument(next, nameof(next));
if (WriteableBitmapExtensions.BitmapsMismatched(unaltered, previous) ||
WriteableBitmapExtensions.BitmapsMismatched(unaltered, next))
{
return(null);
}
WriteableBitmapExtensions.GetColorOffsets(unaltered, out int blueOffset, out int greenOffset, out int redOffset);
int totalPixels = unaltered.PixelWidth * unaltered.PixelHeight;
int pixelSizeInBytes = unaltered.Format.BitsPerPixel / 8;
byte *unalteredIndex = (byte *)unaltered.BackBuffer.ToPointer();
byte *previousIndex = (byte *)previous.BackBuffer.ToPointer();
byte *nextIndex = (byte *)next.BackBuffer.ToPointer();
byte[] differencePixels = new byte[totalPixels * pixelSizeInBytes];
int differenceIndex = 0;
for (int pixel = 0; pixel < totalPixels; ++pixel)
{
byte b1 = (byte)Math.Abs(*(unalteredIndex + blueOffset) - *(previousIndex + blueOffset));
byte g1 = (byte)Math.Abs(*(unalteredIndex + greenOffset) - *(previousIndex + greenOffset));
byte r1 = (byte)Math.Abs(*(unalteredIndex + redOffset) - *(previousIndex + redOffset));
byte b2 = (byte)Math.Abs(*(unalteredIndex + blueOffset) - *(nextIndex + blueOffset));
byte g2 = (byte)Math.Abs(*(unalteredIndex + greenOffset) - *(nextIndex + greenOffset));
byte r2 = (byte)Math.Abs(*(unalteredIndex + redOffset) - *(nextIndex + redOffset));
byte b = WriteableBitmapExtensions.DifferenceIfAboveThreshold(threshold, b1, b2);
byte g = WriteableBitmapExtensions.DifferenceIfAboveThreshold(threshold, g1, g2);
byte r = WriteableBitmapExtensions.DifferenceIfAboveThreshold(threshold, r1, r2);
byte averageDifference = (byte)((b + g + r) / 3);
differencePixels[differenceIndex + blueOffset] = averageDifference;
differencePixels[differenceIndex + greenOffset] = averageDifference;
differencePixels[differenceIndex + redOffset] = averageDifference;
unalteredIndex += pixelSizeInBytes;
previousIndex += pixelSizeInBytes;
nextIndex += pixelSizeInBytes;
differenceIndex += pixelSizeInBytes;
}
WriteableBitmap difference = new WriteableBitmap(BitmapSource.Create(unaltered.PixelWidth, unaltered.PixelHeight, unaltered.DpiX, unaltered.DpiY, unaltered.Format, unaltered.Palette, differencePixels, unaltered.BackBufferStride));
return(difference);
}
// Given two images, return an image containing the visual difference between them
public static unsafe WriteableBitmap Subtract(this WriteableBitmap image1, WriteableBitmap image2)
{
// Check the arguments for null
ThrowIf.IsNullArgument(image1, nameof(image1));
ThrowIf.IsNullArgument(image2, nameof(image2));
if (WriteableBitmapExtensions.BitmapsMismatched(image1, image2))
{
return(null);
}
WriteableBitmapExtensions.GetColorOffsets(image1, out int blueOffset, out int greenOffset, out int redOffset);
int totalPixels = image1.PixelWidth * image1.PixelHeight;
int pixelSizeInBytes = image1.Format.BitsPerPixel / 8;
byte *image1Index = (byte *)image1.BackBuffer.ToPointer();
byte *image2Index = (byte *)image2.BackBuffer.ToPointer();
byte[] differencePixels = new byte[totalPixels * pixelSizeInBytes];
int differenceIndex = 0;
for (int pixel = 0; pixel < totalPixels; ++pixel)
{
byte b = (byte)Math.Abs(*(image1Index + blueOffset) - *(image2Index + blueOffset));
byte g = (byte)Math.Abs(*(image1Index + greenOffset) - *(image2Index + greenOffset));
byte r = (byte)Math.Abs(*(image1Index + redOffset) - *(image2Index + redOffset));
byte averageDifference = (byte)((b + g + r) / 3);
differencePixels[differenceIndex + blueOffset] = averageDifference;
differencePixels[differenceIndex + greenOffset] = averageDifference;
differencePixels[differenceIndex + redOffset] = averageDifference;
image1Index += pixelSizeInBytes;
image2Index += pixelSizeInBytes;
differenceIndex += pixelSizeInBytes;
}
WriteableBitmap difference = new WriteableBitmap(BitmapSource.Create(image1.PixelWidth, image1.PixelHeight, image1.DpiX, image1.DpiY, image1.Format, image1.Palette, differencePixels, image1.BackBufferStride));
return(difference);
}