Pixel access starts at zero
Last updated at 4:47 am UTC on 11 March 2017
Print the following
(Form fromUser) colorAt: 0@0
Example of results
(Color r: 0.796 g: 0.796 b: 0.796)
Note that pixel access starts at 0@0
"Return the color in the pixel at the given point. "
colorFromPixelValue: (self pixelValueAt: aPoint)
depth: self depth
January 04, 2004 Boris Gaertner relied to the following questionf from Martin Kuball
Question: I'm trying to do some image processing in Squeak. I load an image into a Form and than use a BitBlt peeker to examine pixel values. After some hacking I > noticed that the indexing is not 1-based as in other Smalltalk methods. Is > this on purpose or a bug?
Answer: > This is not a bug. In a Form, pixel coordinates run from
0 to: form width - 1
in the horizontal and from
0 to: form height - 1
in the vertical.
This is Smalltalk tradition, but it is not mentioned very often. In the blue book, we read on page 383 (reprint of May 1983):
"A display object represents an image that has a width, a height, an assumed origin at 0 @ 0, and an offset ..."
Recipe: Access a JPEG file pixel by pixel