/// <inheritdoc/>
protected override void OnFrameApply(ImageFrame <TPixel> source, Rectangle sourceRectangle, Configuration configuration)
{
float threshold = this.Threshold * 255F;
Rgba32 rgba = default;
bool isAlphaOnly = typeof(TPixel) == typeof(Alpha8);
var interest = Rectangle.Intersect(sourceRectangle, source.Bounds());
int startY = interest.Y;
int endY = interest.Bottom;
int startX = interest.X;
int endX = interest.Right;
// Collect the values before looping so we can reduce our calculation count for identical sibling pixels
TPixel sourcePixel = source[startX, startY];
TPixel previousPixel = sourcePixel;
PixelPair <TPixel> pair = this.GetClosestPixelPair(ref sourcePixel);
sourcePixel.ToRgba32(ref rgba);
// Convert to grayscale using ITU-R Recommendation BT.709 if required
float luminance = isAlphaOnly ? rgba.A : (.2126F * rgba.R) + (.7152F * rgba.G) + (.0722F * rgba.B);
for (int y = startY; y < endY; y++)
{
Span <TPixel> row = source.GetPixelRowSpan(y);
for (int x = startX; x < endX; x++)
{
sourcePixel = row[x];
// Check if this is the same as the last pixel. If so use that value
// rather than calculating it again. This is an inexpensive optimization.
if (!previousPixel.Equals(sourcePixel))
{
pair = this.GetClosestPixelPair(ref sourcePixel);
// No error to spread, exact match.
if (sourcePixel.Equals(pair.First))
{
continue;
}
sourcePixel.ToRgba32(ref rgba);
luminance = isAlphaOnly ? rgba.A : (.2126F * rgba.R) + (.7152F * rgba.G) + (.0722F * rgba.B);
// Setup the previous pointer
previousPixel = sourcePixel;
}
TPixel transformedPixel = luminance >= threshold ? pair.Second : pair.First;
this.Diffuser.Dither(source, sourcePixel, transformedPixel, x, y, startX, startY, endX, endY);
}
}
}
protected PixelPair <TPixel> GetClosestPixelPair(ref TPixel pixel, TPixel[] colorPalette)
{
// Check if the color is in the lookup table
if (this.cache.ContainsKey(pixel))
{
return(this.cache[pixel]);
}
// Not found - loop through the palette and find the nearest match.
float leastDistance = int.MaxValue;
float secondLeastDistance = int.MaxValue;
var vector = pixel.ToVector4();
var closest = default(TPixel);
var secondClosest = default(TPixel);
for (int index = 0; index < colorPalette.Length; index++)
{
TPixel temp = colorPalette[index];
float distance = Vector4.DistanceSquared(vector, temp.ToVector4());
if (distance < leastDistance)
{
leastDistance = distance;
secondClosest = closest;
closest = temp;
}
else if (distance < secondLeastDistance)
{
secondLeastDistance = distance;
secondClosest = temp;
}
}
// Pop it into the cache for next time
var pair = new PixelPair <TPixel>(closest, secondClosest);
this.cache.Add(pixel, pair);
return(pair);
}
/// <inheritdoc/> public bool Equals(PixelPair <TPixel> other) => this.First.Equals(other.First) && this.Second.Equals(other.Second);