problem after divide image

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wissa amer
wissa amer 2013-6-10
Hello all .. This code to divide the image into blocks, each block 4 * 4 pixels and then find the average of the values of pixels in each block and then put the new values in the image matrix (a) The problem : after storage and display picture shows me a white image why? and Storage in the matrix are not taken properly The value of the average for the first block stored in the last position of the new matrix (a)
if true
I = imread('4.png');
Range_Image=rgb2gray(imread('4.png'));
[m n]=size(Range_Image); Nbrx = floor(m./4);
Nbry = floor(n./4); Nd=1;
for i=1:Nbrx
for j=1:Nbry
Mat=Range_Image((i-1)*4+1:i*4,(j-1)*4+1:j*4);
sumpixel=sum(Mat(:));
avg= floor(sumpixel/16);
a(i,j)=avg;
% subplot(Nbrx,Nbry,Nd); imshow(Mat)
% Nd=Nd+1;
end
end
end

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回答（2 个）

Iain
Iain 2013-6-10
编辑：Iain 2013-6-10
Sounds like either your number format is saturating.
Cast the image as double or single before averaging.
Alternatively use "imagesc" instead of imshow.
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wissa amer
wissa amer 2013-6-10
thank you soo much ..
Iain
Iain 2013-6-11
To cast it as double:
dbl_version = double( Range_Image );

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Image Analyst
Image Analyst 2013-6-10
uint8 images clip at 255 so it you add up 16 uint8 pixels, chances are they will sum to more than 255 and so it will clip at 255. You need to cast to single or double first. Then, if you want values in the same range, you need to divide by 16. Either way, if you want to display it you'll have to use [] as the second argument to imshow(). You can cast back to uint8 if you want the averages to be uint8, like if you want to save the small images or something.
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wissa amer
wissa amer 2013-6-10
imshow(a,[]) i do that.. rigth or wrong
Image Analyst
Image Analyst 2013-6-11
That's right. But like I said, you need to make sure a is of the right type to handle a sum, like uint16 or double, or single.

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