Comments on: All about pixel colors: Truecolor and indexed images

By: Shashidhara

Shashidhara — Wed, 21 Jul 2010 08:06:34 +0000

Dear Steve,

Thanks for your inputs. Your comments really helped me solve the problem. I typecasted ‘y’ to unit8 and it works fine.

Thanks again,

Regards
Shashi

By: Steve

Steve — Tue, 20 Jul 2010 11:53:27 +0000

Yuv—Please contact technical support.

By: Yuv Sharma

Yuv Sharma — Tue, 20 Jul 2010 10:15:13 +0000

Dear steve,
I am quite new to matlab, and have this particular problem or question. Can i take a grayscale image and do some calculations on the cell values, say i want to increase the value of cells which has a value below 50 (say) by 10. After doing such calculations i found that although the resulting matrix showed the calculated results but whenever i used imwrite to write it to a file or use imshow, it either shows a totally black or totally white image. I feel I need to convert the resulting matrix to grayscale, I tried mat2gray and some other commands available in the toolbox but with no use. Hope you can help me.

By: Steve

Steve — Mon, 19 Jul 2010 15:01:12 +0000

Shashidhara—You're using an indexed-image syntax to read the image, and then the rest of the code is assuming that the image is in truecolor format. Also, you are initializing y as a double-precision array but then you're assigning uint8 values into it, so you're going to have a dynamic range scaling problem. I'd like to suggest that you take a look at the Introduction section for the Image Processing Toolbox User Guide to get information about image type and data type conventions.

By: Shashidhara

Shashidhara — Thu, 15 Jul 2010 04:58:51 +0000

Dear Steve, Thanks for kind reply. Here is the part of the code that I am working with;


[m,map]=imread('xyz.bmp');
x=m(:,:,1);
y=zeros(size(m));
y(:,:,1)=x;
figure(1);
imwrite(y,'xyz_RED.bmp','bmp');

I would like to display and write an image with varying only in 'black-red' space. But I get blank image filled with red; i.e., image information that is available if I do

imwrite(x,'xyz_red_gs.bmp','bmp');

is not seen (or lost). Could you please help me how I can solve this. Thanks again, Shashi

By: Steve

Steve — Wed, 14 Jul 2010 11:38:27 +0000

Shashidhara—What do you mean by “this doesn’t work”? What exactly did you try, what was the result, and why was the result not satisfactory?

By: Shashidhara

Shashidhara — Wed, 14 Jul 2010 06:36:06 +0000

Dear Sir,

I would like to display RGB planes as separate images with shades of itself. i.e, I break RGB into R,G, and B planes of 8 bit vectors, and now would like to diplay them as a variation of Black to Red, Black to Green, and Black to Blue. Could you please guide me how I can achieve this in MATLAB.

I have tried to take only one plane and cat them with others planes having ‘zeros’, but this doesn’t work.

Thank you,

Shashi

By: Steve

Steve — Wed, 13 May 2009 23:19:29 +0000

Imen—Use makecform and applycform for converting between RGB and LAB. I don't understand your question about regionprops; that function is for computing geometric measurements of image regions.

By: imen

imen — Wed, 13 May 2009 22:11:09 +0000

hi my problem is how to create a function to convert an image RGB to XYZ then XYZ to LAB and make it “executable” it means i can run it and see the result
and i have another problem ich is how to create a nother function for searching an image using the commande regionprops????
i hope i will get an answer from you

By: Steve

Steve — Wed, 15 Oct 2008 19:53:06 +0000

Anurag—Here's a sample:

RGB = imread('peppers.png');
imshow(RGB)
I = rgb2gray(RGB);
figure, imshow(I)
imwrite(I, peppers_gray.png')