Write a JPEG file to disc.
If three matrices R, G, and B are given the function will write a color image to the disc, where R is the red channel, G the green channel, and B the blue channel of the image.
If only one matrix I is given the function writes a gray-scale image to the disc.
In all cases the data matrices should have integer values between 0 and 255.
If specified, quality should be in the range 1-100 and will default to 75 if not specified. 100 is best quality, and 1 is best compression.