error-output image black in colour

I have a code below for performing CLD ,i have performed till dct coefficient,ids it correct,please guide,in imshow(J),i get only black colour,please help

my image is rgb 

I=imread('dock.jpg'); 
I=rgb2gray(I)
I=imresize(I,[512 512])% I become lena512
fun = @dct2; %dct2 is assigned as function
J = blkproc(I,[64 64],fun); % blkproc function subblocks the image by 8-8 and usign dct2 function
figure
imshow(uint8(J)) % plot the su

Answer 1

[Image Analyst]

What is the type of J? Is it floating point, or complex? Try

imshow(J, []);

instead.

[Pat]

walter the size is 512x512

the matrix has values

0.0002 0.0000 0.0000 0.0001 0.0001 -0.0000 -0.0000 0.0001

-0.0001 -0.0001 0.0000 0.0000 0.0000 -0.0000 -0.0000 -0.0000

0.0001 -0.0000 0.0001 -0.0000 0.0000 0.0000 0.0000 0.0000

-0.0017 -0.0004 0.0002 0.0004 0.0005 0.0012 0.0003 -0.0001

0.0006 0.0004 0.0001 0.0007 0.0003 -0.0011 -0.0008 -0.0003

-0.0003 -0.0000 0.0002 -0.0006 -0.0010 -0.0006 -0.0002 -0.0007

-0.0002 0.0003 -0.0005 -0.0002 0.0010 0.0004 0.0003 0.0004

[Walter Roberson]

I'm relatively sure that Image Analyst's legal name is not Walter.

imshow(J, [])

should be able to handle negative and positive values mixed.

[Walter Roberson]

By the way, if most of the values are near 0, but one of the values is much more (say near 255), then because the entire range of values must be covered, all of the values near 0 could come out black, and the one much larger value would come out white.

Check max(J(:)) and min(J(:))

[Pat]

max(J(:))

1.1508e+004

min(J(:))

-2.8087e+003

[Image Analyst]

That's fine, just know that imshow is linear - it linearly scales your data between 0 and 255 for display. If you have a really skewed distribution or some real outlier values (like salt and pepper noise), you can either reassign them or run your image through imadjust().

[Pat]

Will i get output as per the link below,since an working on CLD

http://en.wikipedia.org/wiki/Color_layout_descriptor

[Image Analyst]

No. imshow() simply displays the image - it's not a whole complicated image processing technique like that.

[Pat]

walter can u tell how to display image as like that

[Image Analyst]

As like *what*??? We told you how to display images.

[Walter Roberson]

I'm still relatively sure that Image Analyst's legal name is not Walter.

[Pat]

Sorry walter,MR.Image Analyst,as i wikipedia i want those two images ,that i,age divided into 64 blocks,and color representation,if else please can u send the full coding for cld

[Image Analyst]

I've never used CLD so I don't have any code for it, so you're on your own. Walter's right, though it's a very fine and respectable name, my name isn't Walter.

[Pat]

OK Image Analyst