我正在实现Java PNG编码器。我在对AVG和Paeth过滤器进行编码时遇到了问题。
我知道我的问题出在计算的某处（使用字节进行计算），但是我只是找不到正确的设置来使其工作。
这些是我的过滤器，然后是原始img的图片以及每一个的最终结果。
在此先感谢您提供的任何帮助！
过滤器：
/*
* Filter based on diff with AVG of previous & above pixels. First pixel in
* each line, and the first line, are copied as is.
* pixdat[] = the original img byte array
* @param1: scanLines: 1 line of bytes (line length=width*3 (3b per
* pixel)
* @param2: line: current line in original image data
* @return resulting lines of filtered values (byte array)
*/
protected byte[] filterAVG(byte[] scanLine,int line) {
byte[] temp = new byte[scanLine.length];
temp[0] = scanLine[0];
temp[1] = scanLine[1];
temp[2] = scanLine[2];
double avg;
for (int i = 3; i < scanLine.length; i++) {
avg=(Math.floor((scanLine[i - 3] + pixdat[(line-1)*width*3+i])/2));
temp[i] = (byte) (scanLine[i] - avg);
}
return temp;
}
/*
* Filter based on paeth linear equation; First pixel in each line, and the
* first line, are copied as is. if a=prev pixel, b= pixel above, c = pixel
* above and to the left then: p=a+b-c. answer=the smallest diff between
* pa,pb,pc.
*
* @param scanLines: 1 or more lines of bytes (line length=width*3 (3b per
* pixel)
* @param2: line: current line in original image data
* @return resulting lines of filtered values (byte array)
*/
protected byte[] filterPaeth(byte[] scanLine,int line) {
byte[] temp = new byte[scanLine.length];
temp[0]=scanLine[0];
temp[1]=scanLine[1];
temp[2]=scanLine[2];
for (int i = 3; i < scanLine.length; i++) {
temp[i]=(byte) ((scanLine[i]&0xff-paethPredictor(scanLine, i, line)));
}
return temp;
}
protected int paethPredictor(byte[] temp,int i,int line){
int p,pa,pb,pc;
int a = temp[i - 3], b = pixdat[(line-1)*width*3+i], c = pixdat[(line-1)*width*3+i - 3];
p = (a + b - c); //; initial estimate
pa = Math.abs(p&0xff - a&0xff); //; distances to a, b, c
pb = Math.abs(p&0xff - b&0xff);
pc = Math.abs(p&0xff - c&0xff);
// return nearest of a,b,c,
// breaking ties in order a,b,c.
if (pa <= pb && pa <= pc) return a;
else if (pb <= pc) return b;
else return c;
}
