When using imread function, the blank area automatic as 255. How to turn the pixel of blank area as empty?

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Mei Synn Tan 2017-5-3

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rgb_image = imread('13100 IP.jpg');

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Walter Roberson 2017-5-3

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That is not possible with .jpg files. .jpg files can only store integral values, and cannot store an Alpha channel.

If you want to store information about which positions are empty, you will need to use a different image file format; in particular imwrite() PNG image file and either the 'alpha' or 'transparency' options. It is also possible to create alpha channels in TIFF images if you use the Tiff() class.