Compare the size of an all-white image in JPEG format with a "typical" photographic image of the same dimensions. At what stage or stages of the JPEG compression process does the white image become smaller than the photographic image? For the next three exercises, the utilities cjpeg and djpeg may be useful and can be obtained from ftp.uu.net/graphics/jpeg. Other JPEG conversion utilities can also be used.
For manual creation and examination of graphics files, the pgm portable grayscale format is recommended; see the Unix pgm(5)/ppm(5) man pages.