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How to get average of a set of images |
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The following Java method takes an array of BufferedImage objects and returns average image
obtained from the array of images.
The main application of image averaging is noise removal. Image noise is mostly unwanted
and manifested in the pixels of an image. It is inherent to digital cameras, and
is generated, in part, by heat and low light conditions, and is often prominent in
long exposures and photographs taken at high ISO sensitivity.
Its effect is analagous to film grain.
When images of an unchanging scene are corrupted by random noise, a sequence of these
images can be averaged together in order to reduce the effects of the noise. This
works because noise perturbs pixel grey levels, and a positive perturbation of a
given magnitude tends to be just as likely as a negative perturbation of the same
magnitude. Hence there is a tendency for these 'errors' in pixel grey level to
cancel each other out to an increasing degree, as the number of averaged
images increases.
Although the example is written for grey level images, you can change the method
for applying it to RGB images easily. You will just need to compute average value for
each channel (Red,Green or Blue channel).
public static BufferedImage average(BufferedImage[] images) {
int n = images.length;
// Assuming that all images have the same dimensions
int w = images[0].getWidth();
int h = images[0].getHeight();
BufferedImage average =
new BufferedImage(w, h, BufferedImage.TYPE_BYTE_GRAY);
WritableRaster raster =
average.getRaster().createCompatibleWritableRaster();
for (int y=0; y < h; ++y)
for (int x=0; x < w; ++x) {
float sum = 0.0f;
for (int i=0; i<n; ++i)
sum = sum + images[i].getRaster().getSample(x, y, 0);
raster.setSample(x, y, 0, Math.round(sum/n));
}
average.setData(raster);
return average;
}
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