Pixel values in grayscale images

[kedarm]

Hi!

This is just something I am trying out. The idea is to get a little familiar with Python and its image processing capabilities before building any application. I am having some doubts on the jpeg compression type. I am using the graphics module.

>>> import graphics

To start with, I created a (blank) grayscale image and saved it (right away) with the following commands :

>>> im = graphics.Image.new((200,200),"L")
>>> im.save("D:\\blank.jpg", quality=100, bpp=1, compression="no"

As expected, this gave me a blank image. However, when I check its pixel values, it doesn't give me a single byte, but gives me a triplet (RGB values?)

>>> im.getpixel((23,123))
(255,255,255)

I also tried loading the newly created image into another image and checked the pixel values :

>>> bg = graphics.Image.open("D://blank.jpg")
>>> bg.getpixel((23,123))
(255,255,255)

My question is, if the image is a grayscale image, why is the pixel value a triplet, and not a byte? Shouldn't the output for a grayscale image be something along the lines of :

>>> bg.getpixel((23,123))
X (where X is a number between 0 and 255)

Thanks
Kedar

[mrblombe]

getpixel is an undocumented function, which always returns a rgb-triplet.

A grayscale image has identical values of red, green and blue thus being gray.
Therefore the resulting (255, 255, 255) is correct as the getpixel function always returns a tuple with red, green and blue values regardless of display mode i.e. bit amount.

More in this thread.

[kedarm]

Thanks..

I guess I accidentally stumbled upon the same method in a totally different way! Lucky me!

Thanks..