/// <summary>
/// Analyzes image colors and creates color map.
/// </summary>
private void AnalyzePixels()
{
if (this.firstFrame)
{
// HEY YOU - THIS IS IMPORTANT!
//
// Unlike the code this project is built on, we generate a palette only once, using the data from the
// first frame. This speeds up encoding (building the palette is slow) and makes it so that subsequent
// frames use the same colors and look more consistent from frame to frame, but has an undesirable
// side-effect of getting confused when radically different colors show up in later frames. This wasn't
// a problem with Infinifactory, but if your game uses a deliberately reduced color palette you might
// want to switch back to using per-frame palettes.
//
// This is, of course, left as an exercise for the reader.
// initialize quantizer and create reduced palette
this.nq = new NeuQuant(this.pixels, this.pixels.Length, this.sample);
this.colorTab = nq.Process();
// create the buffer for the displayed pixel data:
this.visiblePixels = new byte[this.pixels.Length];
}
int nPix = this.pixels.Length / 3;
this.indexedPixels = new byte[nPix];
// map image pixels to new palette
for (int i = 0; i < nPix; i++)
{
int r = i * 3 + 0;
int g = r + 1;
int b = g + 1;
// HEY YOU - THIS IS IMPORTANT!
//
// As you may know, animated GIFs aren't exactly the most efficient way to encode video; notably,
// they lack the interframe compression found in real video formats. However, we can do something
// similar by taking advantage of the GIF format's ability to "build on" a previous frame by
// specifying pixels as transparent and allowing the previous frame's image to show through in those
// locations. If a pixel doesn't change much from a previous pixel it will be replaced with the
// transparent color, and if enough of those pixels are used in a frame it will compress much better
// than if you had all the original color data for the frame.
//
// In a game like Infinifactory, where the recording camera is locked and only a small portion of
// the scene is animated, this reduced the size of GIFs to about 1/3 of their original size.
const int ChangeDelta = 3;
bool pixelRequired = this.firstFrame ||
Math.Abs(this.pixels[r] - this.visiblePixels[r]) > ChangeDelta ||
Math.Abs(this.pixels[g] - this.visiblePixels[g]) > ChangeDelta ||
Math.Abs(this.pixels[b] - this.visiblePixels[b]) > ChangeDelta;
int index;
if (pixelRequired)
{
this.visiblePixels[r] = this.pixels[r];
this.visiblePixels[g] = this.pixels[g];
this.visiblePixels[b] = this.pixels[b];
index = this.nq.Map(this.pixels[r], this.pixels[g], this.pixels[b]);
}
else
{
index = NeuQuant.PaletteSize;
}
this.usedEntry[index] = true;
this.indexedPixels[i] = (byte)index;
}
this.colorDepth = (int)Math.Log(NeuQuant.PaletteSize + 1, 2);
this.palSize = this.colorDepth - 1;
}
/**
* Analyzes image colors and creates color map.
*/
protected void AnalyzePixels()
{
int len = pixels.Length;
int nPix = len / 3;
indexedPixels = new byte[nPix];
NeuQuant nq = new NeuQuant(pixels, len, sample);
// initialize quantizer
colorTab = nq.Process(); // create reduced palette
// convert map from BGR to RGB
// for (int i = 0; i < colorTab.Length; i += 3)
// {
// byte temp = colorTab[i];
// colorTab[i] = colorTab[i + 2];
// colorTab[i + 2] = temp;
// usedEntry[i / 3] = false;
// }
// map image pixels to new palette
int k = 0;
for (int i = 0; i < nPix; i++)
{
int index =
nq.Map(pixels[k++] & 0xff,
pixels[k++] & 0xff,
pixels[k++] & 0xff);
usedEntry[index] = true;
indexedPixels[i] = (byte) index;
}
pixels = null;
colorDepth = 8;
palSize = 7;
// get closest match to transparent color if specified
if (transparent != Color.Empty )
{
transIndex = FindClosest(transparent);
}
}
