在Photoshop中，有一种滤镜可以让图像看起来像是历经岁月，呈现出微微泛黄的效果。这种图像特效在英文中被称为Sepia Tone Effect,直译过来的意思就是黄褐色特效。其基本处理算法如下：
1. 首先对图像重新计算RGB值，计算公式如下：
```java
int fr = (int) (((double) tr * 0.393) + ((double) tg * 0.769) + ((double) tb * 0.189));
int fg = (int) (((double) tr * 0.349) + ((double) tg * 0.686) + ((double) tb * 0.168));
int fb = (int) (((double) tr * 0.272) + ((double) tg * 0.534) + ((double) tb * 0.131));
```
2. 对图像计算出来的新的RGB值根据随机权重与旧值混合。计算随机权重的代码如下：
```java
private double noise() {
return Math.random() * 0.5 + 0.5;
}
```
混合颜色的代码如下：
```java
private double colorBlend(double scale, double dest, double src) {
return (scale * dest + (1.0 - scale) * src);
}
```
经过以上处理后，图像呈现出了黄褐色的效果。
```java
package comgloomyfish.filter.study;
import java.awt.image.BufferedImage;
public class SepiaToneFilter extends AbstractBufferedImageOp {
@Override
public BufferedImage filter(BufferedImage src, BufferedImage dest) {
int width = src.getWidth();
int height = src.getHeight();
if (dest == null) {
dest = createCompatibleDestImage(src, null);
}
int[] inPixels = new int[width * height];
int[] outPixels = new int[width * height];
getRGB(src, 0, 0, width, height, inPixels);
int index = 0;
for (int row = 0; row < height; row++) {
int ta = 0, tr = 0, tg = 0, tb = 0;
for (int col = 0; col < width; col++) {
index = row * width + col;
ta = (inPixels[index] >> 24) & 0xff;
tr = (inPixels[index] >> 16) & 0xff;
tg = (inPixels[index] >> 8) & 0xff;
tb = inPixels[index] & 0xff;
int fr = (int) colorBlend(noise(), (tr * 0.393) + (tg * 0.769) + (tb * 0.189), tr);
int fg = (int) colorBlend(noise(), (tr * 0.349) + (tg * 0.686) + (tb * 0.168), tg);
int fb = (int) colorBlend(noise(), (tr * 0.272) + (tg * 0.534) + (tb * 0.131), tb);
outPixels[index] = (ta << 24) | (clamp(fr) << 16) | (clamp(fg) << 8) | clamp(fb);
}
}
setRGB(dest, 0, 0, width, height, outPixels);
return dest;
}
private double noise() {
return Math.random() * 0.5 + 0.5;
}
private double colorBlend(double scale, double dest, double src) {
return (scale * dest + (1.0 - scale) * src);
}
public static int clamp(int c) {
return c > 255 ? 255: (c < 0) ? 0: c;
}
public String toString() {
return "Sepia Tone Effect - Effect from Photoshop App";
}
}
```
