Each pixel records an intensity level from 0 to 255 for each of the red, green, and blue channels. Since there are three channels per pixel, the total image size is 3 times 3.3 Mpix, or close to 10 megabytes. It takes 8 bits to represent a number up to 255 as a byte, so the camera is said to operate in 24-bit mode. However, such large files are slow to manipulate and would rapidly fill your memory card. The camera therefore gives you the option of compressing image files as they move into the buffer.
File compression has two great advantages.
Since the image files are smaller, you can store more on a single memory card. For bird photography, an equally important benefit is that you can take more photos in rapid succession if the files are smaller. This process takes several agonizing seconds during which the camera is unresponsive. However, if the image files are small, several can fit into the buffer before it flushes. Because birds are dynamic, you may capture several interesting poses as the bird moves, looks around, tends to nestlings, etc.