When using imread, changed the background colour of image?

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Samyukta Ramnath 2013-7-14

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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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Answer 1

Image Analyst 2013-7-14

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在 MATLAB Online 中打开

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 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 2013-7-16