Question

I have a raw image where each pixel corresponds to a 16 bits unsigned integer. I am trying to read using the PIL Image.fromstring() function as in the following code:

if __name__ == "__main__":
    if (len(sys.argv) != 4):
        print 'Error: missing input argument'
        sys.exit()

    file = open(sys.argv[1], 'rb')
    rawData = file.read()
    file.close()

    imgSize = (int(sys.argv[2]), int(sys.argv[3]))

    # Use the PIL raw decoder to read the data.
    #   - the 'F;16' informs the raw decoder that we are reading a little endian, unsigned integer 16 bit data.
    img = Image.fromstring('L', imgSize, rawData, 'raw', 'F;16')

    im.save('out.png')

The PIL documentation informs that the first argument of the fromstring() function is ‘mode’. However, looking at the documentation and googling I wasn’t able to find details about what that argument really means (I believe that it is related to the color space or something like that). Does anyone knows where I can find a more detailed reference about the fromstring() function and what the mode argument means?

Answer 1

The specific documentation is at http://effbot.org/imagingbook/concepts.htm:

Mode

The mode of an image defines the type
and depth of a pixel in the image. The
current release supports the following
standard modes:

• 1 (1-bit pixels, black and white, stored with one pixel per byte)
• L (8-bit pixels, black and white)
• P (8-bit pixels, mapped to any other mode using a colour palette)
• RGB (3×8-bit pixels, true colour)
• RGBA (4×8-bit pixels, true colour with transparency mask)
• CMYK (4×8-bit pixels, colour separation)
• YCbCr (3×8-bit pixels, colour video format)
• I (32-bit signed integer pixels)
• F (32-bit floating point pixels)

PIL also provides limited support for
a few special modes, including LA (L
with alpha), RGBX (true colour with
padding) and RGBa (true colour with
premultiplied alpha).