internal void Insert(Argb color)
{
if (this.Bits > 0)
{
this.Array[this.Index(color)] = color;
}
}
/// The palette (color-indexing) transform replaces pixels with indices into
/// a palette that is stored before the image data. If the palette is
/// sufficiently small, multiple indices are packed into a single pixel.
internal static Image PaletteTransform(BitWriter b, Image image, Palette palette)
{
b.WriteBits(1, 1);
b.WriteBits(3, 2);
WritePalette(b, palette);
int packSize =
palette.Count <= 2 ? 8 :
palette.Count <= 4 ? 4 :
palette.Count <= 16 ? 2 : 1;
int packedWidth = (image.Width + packSize - 1) / packSize;
var palettized = new Image(packedWidth, image.Height);
for (int y = 0; y < image.Height; ++y)
{
for (int i = 0; i < packedWidth; ++i)
{
int pack = 0;
for (int j = 0; j < packSize; ++j)
{
int x = i * packSize + j;
if (x >= image.Width)
{
break;
}
int colorIndex = palette.Indices[image[x, y]];
pack |= colorIndex << (j * (8 / packSize));
}
palettized[i, y] = new Argb(255, 0, (byte)pack, 0);
}
}
return(palettized);
}
static Argb ClampAddSubtractHalf(Argb a, Argb b)
{
return(new Argb(
Clamp(a.A + (a.A - b.A) / 2),
Clamp(a.R + (a.R - b.R) / 2),
Clamp(a.G + (a.G - b.G) / 2),
Clamp(a.B + (a.B - b.B) / 2)));
}
static Argb ClampAddSubtractFull(Argb l, Argb t, Argb tl)
{
return(new Argb(
Clamp(l.A + t.A - tl.A),
Clamp(l.R + t.R - tl.R),
Clamp(l.G + t.G - tl.G),
Clamp(l.B + t.B - tl.B)));
}
static Argb Average2(Argb a, Argb b)
{
return(new Argb(
(byte)((a.A + b.A) / 2),
(byte)((a.R + b.R) / 2),
(byte)((a.G + b.G) / 2),
(byte)((a.B + b.B) / 2)));
}
internal static uint Hash(Argb argb)
{
uint x1 = argb.ToUInt();
uint x2 = (x1 * 47491) ^ ~(x1 * 41227);
uint x3 = x2 * (x2 << 3) ^ ~(x2 >> 5) ^ (x2 >> 13);
uint x4 = (x3 * 20389) ^ ~(x3 * 28111);
return(x4);
}
internal bool Lookup(Argb color, out int index)
{
if (this.Bits <= 0)
{
index = 0; return(false);
}
index = this.Index(color);
return(this.Array[index] == color);
}
internal static uint Hash(Argb a1, Argb a2, Argb a3)
{
uint h1 = Hash(a1);
uint h2 = Hash(a2);
uint h3 = Hash(a3);
uint x1 = h1 ^ (h2 * 32369) ^ ~(h3 * 39217);
uint x2 = ~(h1 * 40483) ^ h2 ^ (h3 * 42943);
uint x3 = (x1 << 3) ^ (x2 >> 7);
return(x3);
}
static Argb Select(Argb l, Argb t, Argb tl)
{
int pA = l.A + t.A - tl.A;
int pR = l.R + t.R - tl.R;
int pG = l.G + t.G - tl.G;
int pB = l.B + t.B - tl.B;
int pL = Abs(pA - l.A) + Abs(pR - l.R) + Abs(pG - l.G) + Abs(pB - l.B);
int pT = Abs(pA - t.A) + Abs(pR - t.R) + Abs(pG - t.G) + Abs(pB - t.B);
return(pL < pT ? l : t);
}
/// The prediction transform predicts the values of pixels using their
/// already decoded neighbors, storing only the difference between the
/// predicted and actual value. There are 14 prediction modes and which mode
/// is used is determined from an encoded subsample image.
internal static Image PredictTransform(BitWriter b, Image image)
{
b.WriteBits(1, 1);
b.WriteBits(0, 2);
int tileBits = 4;
int tileSize = 0;
int blockedWidth = 0;
int blockedHeight = 0;
while (tileBits < 2 + 8)
{
tileSize = 1 << tileBits;
blockedWidth = (image.Width + tileSize - 1) / tileSize;
blockedHeight = (image.Height + tileSize - 1) / tileSize;
if (blockedWidth * blockedHeight < 2000)
{
break;
}
++tileBits;
}
b.WriteBits(tileBits - 2, 3);
var blocks = new Image(blockedWidth, blockedHeight);
var residuals = new Image(image.Width, image.Height);
var accumHistos = Enumerable.Range(0, 4).Select(_ => new Histogram(256)).ToList();
for (int y = 0; y < blockedHeight; ++y)
{
for (int x = 0; x < blockedWidth; ++x)
{
int bestPrediction = 0;
double bestEntropy = PredictEntropy(image, tileBits, x, y, 0, accumHistos);
for (int i = 1; i < PREDICTIONS.Count; ++i)
{
double entropy = PredictEntropy(image, tileBits, x, y, i, accumHistos);
if (entropy < bestEntropy)
{
bestPrediction = i;
bestEntropy = entropy;
}
}
blocks[x, y] = new Argb(255, 0, (byte)bestPrediction, 0);
PredictBlock(image, residuals, tileBits, x, y, bestPrediction, accumHistos);
}
}
ImageData.WriteImageData(b, blocks, false);
return(residuals);
}
/// Computes all the histograms from an image.
static List <Histogram> ComputeHistograms(Image image,
Palette paletteOrNull, out bool hasAlpha)
{
var histos = Enumerable.Range(0, (int)HistogramIdx._COUNT)
.Select(_ => new Histogram(256)).ToList();
Argb previous = new Argb(255, 0, 0, 0);
hasAlpha = false;
for (int i = 0; i < image.Pixels.Length; ++i)
{
Argb pixel = image.Pixels[i];
if (pixel.A != 255)
{
hasAlpha = true;
}
Argb delta = pixel - previous;
previous = pixel;
histos[(int)HistogramIdx.RED].Hit(pixel.R);
histos[(int)HistogramIdx.GREEN].Hit(pixel.G);
histos[(int)HistogramIdx.BLUE].Hit(pixel.B);
histos[(int)HistogramIdx.ALPHA].Hit(pixel.A);
histos[(int)HistogramIdx.DELTA_RED].Hit(delta.R);
histos[(int)HistogramIdx.DELTA_GREEN].Hit(delta.G);
histos[(int)HistogramIdx.DELTA_BLUE].Hit(delta.B);
histos[(int)HistogramIdx.DELTA_ALPHA].Hit(delta.A);
histos[(int)HistogramIdx.RED_MINUS_GREEN].Hit((byte)(pixel.R - pixel.G));
histos[(int)HistogramIdx.BLUE_MINUS_GREEN].Hit((byte)(pixel.B - pixel.G));
histos[(int)HistogramIdx.DELTA_RED_MINUS_DELTA_GREEN]
.Hit((byte)(delta.R - delta.G));
histos[(int)HistogramIdx.DELTA_BLUE_MINUS_DELTA_GREEN]
.Hit((byte)(delta.B - delta.G));
if (paletteOrNull != null)
{
histos[(int)HistogramIdx.PALETTE].Hit(paletteOrNull.Indices[pixel]);
}
}
return(histos);
}
/// Computes the predicted value for a single image pixel given the
/// prediction mode.
static Argb Predict(Image image, int x, int y, int prediction)
{
if (x == 0 && y == 0)
{
return(new Argb(255, 0, 0, 0));
}
else if (x == 0)
{
return(image[x, y - 1]);
}
else if (y == 0)
{
return(image[x - 1, y]);
}
int i = y * image.Width + x;
Argb top = image.Pixels[i - image.Width];
Argb left = image.Pixels[i - 1];
Argb topLeft = image.Pixels[i - image.Width - 1];
Argb topRight = image.Pixels[i - image.Width + 1];
return(PREDICTIONS[prediction](top, left, topLeft, topRight));
}
private int Index(Argb color)
{
return((int)((uint)(color.ToUInt() * 0x1e35a7bd) >> (32 - this.Bits)));
}
internal void AddChain(Argb a1, Argb a2, Argb a3, int index)
{
int i = (int)(Argb.Hash(a1, a2, a3) % this.Chains.Count());
this.Chains[i] = new Chain(this.Chains[i], index);
}
internal Chain GetChain(Argb a1, Argb a2, Argb a3)
{
return(this.Chains[(int)(Argb.Hash(a1, a2, a3) % this.Chains.Count())]);
}