Why imwrite doesn't work??

2018 3 1
1 个回答
更新时间：2018 3 1
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I have a .mat file of Lena(greyscale) and i want to use imwrite to trnsfer it to a jpeg file. so i used:
load Lena;
imwrite (Lena, 'lena.jpg')
there is a jpeg file being generated but it is all white (all values are 255). I don't know why is that?

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Stephen23
Stephen23 2018-3-1
@Chen Ji: please show us the outputs of these commands:
class(Lena)
max(Lena(:))
Chen Ji
Chen Ji 2018-3-1
Oh! I worked out caz i found that the input matrix for imwrite should in [0,1] and my Lena element range is in [0,255]. Then i divide each element by 255 and then it worked. It should be a correct solution, right? Thx!!!
Stephen23
Stephen23 2018-3-1
编辑：Stephen23 2018-3-1
"found that the input matrix for imwrite should in [0,1] "
This is not correct: the input range actually depends on the image data class. If you have an image of class double then dividing by 255 may work, see my answer for another solution.
Chen Ji
Chen Ji 2018-3-1
I used the code in your answer and the commend is "double" and 240

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Stephen23
Stephen23 2018-3-1
编辑：Stephen23 2018-3-1

1 个投票

Your image has double values on range [0,255], so you need to scale the values to [0,1] or change the class:
imwrite(uint8(Lena), 'lena.jpg')
imwrite(Lena/255, 'lena.jpg')

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2018-3-1

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