How to Achieve Effective Color Quantization for Animated GIFs in Java?

Effective Color Quantization for Animated GIFs

In Java, the quantization algorithm you mentioned (found at http://www.java2s.com/Code/Java/2D-Graphics-GUI/Anefficientcolorquantizationalgorithm.htm) appears to be lacking precision for images with more than 256 colors. To enhance color quantization, consider the following alternatives:

Alternative Algorithms:

• Median cut
• Population
• K-means

Approach for Fast and Efficient Quantization:

• Convert to 15-bit RGB (or 5:6:5 scheme for better results).
• Create a histogram to count pixel occurrences.
• Reorder the histogram to eliminate zero values.
• Sort the histogram to arrange colors in descending order based on pixel count.
• Create a palette of N colors, adding only unique colors from the sorted histogram until the palette is complete.
• Map each color in the original image to the closest color in the palette.
• Recolor the image using the color mapping table.

Sample Code in C :

// Histogram and index arrays
DWORD his[32768];
DWORD idx[32768];

// Recolor mapping table
BYTE recolor[32][32][32];

// Extract 15-bit RGB from 32-bit RGB
cc=((cc>>3)&0x1F)|((cc>>6)&0x3E0)|((cc>>9)&0x7C00);

// Histogram counting
his[cc]++;

// Reorder and sort histogram
for (x=0,y=0;y<32768;y++)
{
    his[x]=his[y];
    idx[x]=idx[y];
    if (his[x]) x++;
}
hists=x;
for (i=1;i;)
    for (i=0,x=0,y=1;y<hists;x++,y++)
        if (his[x]<his[y])
        {
            i=his[x]; his[x]=his[y]; his[y]=i;
            i=idx[x]; idx[x]=idx[y]; idx[y]=i; i=1;
        }

// Create color palette
for (i0=0,x=0;x<hists;x++)
{
    cc=idx[x];
    b= cc     &amp;31;
    g=(cc>> 5)&amp;31;
    r=(cc>>10)&amp;31;
    c0.db[0]=b;
    c0.db[1]=g;
    c0.db[2]=r;
    c0.dd=(c0.dd<<3)&amp;0x00F8F8F8;

    // Find closest color in palette
    int dc=-1; DWORD ii=0;
    for (a=0,i=0;i<i0;i++)
    {
        aa=int(BYTE(c1.db[0]))-int(BYTE(c0.db[0])); if (aa<=0) aa=-aa; a =aa;
        aa=int(BYTE(c1.db[1]))-int(BYTE(c0.db[1])); if (aa<=0) aa=-aa; a+=aa;
        aa=int(BYTE(c1.db[2]))-int(BYTE(c0.db[2])); if (aa<=0) aa=-aa; a+=aa;
        if ((dc<0)||(dc>a)) { dc=a; ii=i; }
    }
    recolor[r][g][b]=ii;
}

// Recolor image using mapping table
pyx [y][x]=lcolor[recolor[r][g][b]];

This approach provides faster and more accurate color quantization. The specific algorithm and parameters to use may vary depending on the input images and desired outcomes.

The above is the detailed content of How to Achieve Effective Color Quantization for Animated GIFs in Java?. For more information, please follow other related articles on the PHP Chinese website!