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Preston_5564C06.fm Page 196 Friday, September 23, 2005 5:13 AM

196 CHAPTER 6 ■ VISION

Figure 6-15. The blue threshold

Still another way to use color is to filter it. So, rather than getting certain color components,
I’ll just show certain colors as greyscale images.

Code Objective
In this section, the objective is to use a color filter to show only the red pixels of an image in
greyscale, where higher reds appear white, and lower reds appear black.

Code Discussion

Here, instead of thresholding, we’re just converting the red components of an image into grey-
scale. See Example 6-17 and Figure 6-16.

Example 6-17. filterColor()
public BufferedImage filterColor(BufferedImage srcImg, Color c) {
int h = srcImg.getHeight();
int w = srcImg.getWidth();

BufferedImage dstImg = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);

for (int y = 0; y < h; ++y) {
for (int x = 0; x < w; ++x) {
int srcPixel = srcImg.getRGB(x, y);
int colorValue = 0;
// gets colors
if (c == null) {
colorValue = getGrey(srcPixel);
} else if (c == Color.RED) {
colorValue = new Color(srcPixel).getRed();