Why does imshow() function in Matlab return a blank image?

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Akshra
Akshra 2016-12-8
回答： Kushagr Gupta 2016-12-20
I am trying to perform the inverse stationary wavelet transform on an image, but I can't view the output of the image using the imshow() or image(), they both return a blank figure. I have also tried imshow(Y,[]) this also returns a blank image.
This is what I am trying to do
[A,H,D,V] = swt2(i,3,'sym4'); %input i is an grayscale/intensity image%
Y = iswt2(A,H,D,V, 'sym4') ;
imshow(Y) % the figure is white/blank %
How can I resolve this issue?
  1 个评论
Adam
Adam 2016-12-8
编辑：Adam 2016-12-8
Have you used the debugger to actually look at Y and see if there is anything in it? The most obvious reason why imshow and image return a blank image is because you are giving them blank data to plot.
Also double-check data types.

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回答（1 个）

Kushagr Gupta
Kushagr Gupta 2016-12-20
Another common mistake that can yield to white or black images is a mismatch in datatypes while casting from one to another.
For example:
>> I1 = im2double(imread('coins.png')); % reads an image and converts to double in range 0-1
>> imshow(uint8(I1)) % yields a black image
This happened as the image within range [0 1] was cast into uint8 whose range is [0 255]
A better way to cast, if it is required at all would be:
>> imshow(uint8(I1*255));
But in general it is a good practice to deal with images converted to double datatype using ' im2double ' and doing further processing on these matrices.

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