When using imread, changed the background colour of image?

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Samyukta Ramnath
Samyukta Ramnath 2013-7-14
I had an image of a red cross with a background colour of white, after I used imread, it returned an image with a black background. Why is this? And, does it have anything to with the file format? (.png) This is messing with the entire program.

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Image Analyst
Image Analyst 2013-7-14
Extract the color channels and see what the values are
% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
Then pick a row and column that's in the background and see what they are
r = redChannel(row, column)
g = greenChannel (row, column)
b = blueChannel (row, column)
Tell us what your values are.
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Image Analyst
Image Analyst 2013-7-15
If it's a uint8 image, the values should be integers going from 0 to 255. If you have a double image (floating point) then all values must be in the range 0-1 if you want to display them with imshow(). [0,0,0] is pure black. [0,0,1] is pure blue. [1,1,1] is pure white. Any transparent pixels in your PNG image will show up in the "BG" color. Maybe your background is not really transparent like you thought.
Samyukta Ramnath
Samyukta Ramnath 2013-7-16
This makes sense, because when I try the same thing (setting the background color for another image), it gives an error.

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