Find color of specific pixels

I'm working with grayscale images and I need to find average darkness of specific regions. The areas are all perfectly circular.
I can't figure out how to determine the color of specific pixels in an image. Does anyone know of a way? I need to process millions of pixels so I would prefer something that can do this relatively quickly. The images are all grayscale, so I only really need to know the darkness of the pixel.
I don't suppose there is any built-in way of doing this that would be more efficient than my computing the average manually?

Ok, it seems that I can use a BufferedImage to acquire the colors of specific pixels. I found a couple methords that seem relavent:
public int getRGB(int x, int y)
public int[] getRGB(int startX, int startY, int w, int h, int[] rgbArray, int offset, int scansize)
The first is pretty staight forward, but I am interested in performance, and the second sounds like it could be better.
I'm not sure about the meaning of the the scansize argument:
scansize - scanline stride for the rgbArray
Am I right in thinking that rgbArray is defined that the value in the first index (after offset) is the upper left corner, the next is the pixel directly to the right of it. When the index become equal to scanline, you are now on the next row of pixels below.
This doesn't make sense to me because it would defeat the purpose of having 'w' (the width).
Now, the other question is whether using the second methord will actually improve performance...I need circular regions, so using a rectangle will waste data. Would I be better off using getRGB(int x, int y)? How about creating a subclass of BufferedImage designed to extract the colors in a circular manner. Actually, is using a BufferedImage the best approach even?

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