changing the rgb values of the pixels in a jpg image

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roshana
roshana 2011-4-6
编辑： Walter Roberson 2017-7-16
J=imread('A.jpg');
for i=1:r
for j=1:c
J(i,j,1)=newrgb(1,1);
J(i,j,2)=newrgb(1,2);
J(i,j,3)=newrgb(1,3);
end
end
%%newrgb is a matrix with 3 rgb values.
when I check the newrgb matrix, it has double values larger than one,i guess 1 to 255.
I know imread gives me values of uint8, but i tried converting the newrgb values to uint8, or even converting the rgb of my image to double, but the result is a white picture, what should i do?
thank you
  1 个评论
Poornakant
Poornakant 2017-7-15
Hello Roshana, I'm working on something similar to this question of yours. Changing the RGB values of a pixel to get a specific curve of an image. I'm new to MATLAB coding could you please help me with the method you've used to sort your problem. Thank you.

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回答（3 个）

Walter Roberson
Walter Roberson 2011-4-6
Replace your 3 existing assignments with
J(i,j,:) = newrgb .* 255;
  2 个评论
roshana
roshana 2011-4-6
still not working. you see the rgb values of J are in uint8.when I divide the newrgb values by 255, instead of multiplying, it gives me a maroon picture. in case of multiplying it is only a white page
Walter Roberson
Walter Roberson 2011-4-6
What value range is newrgb ? And what data class is the variable?

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roshana
roshana 2011-4-7
newrgb values are between 1 to 100, and of type double.
  1 个评论
Walter Roberson
Walter Roberson 2011-4-7
If J is uint8 and your newrgb values are in the range you indicate, then your original code will set the entire block J(1:r,1:c,:) to be the color indicated by newrgb. If r and c are the size of J then the result would be a monochrome picture. If the values in newrgb are all the same, then the monochrome picture would be a shade of gray.
After you assign the values, look at J(1,1,:) to see whether the values match the (rounded) values of newrgb .

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roshana
roshana 2011-4-7
the problem is solved. it seems matlab kept the previous wrong answer in the memory in a way. I came to know this when I changed my image, the result was still the previous image, I totally changed the variable, and it works. Maybe because I used J as image variable, and j as the loop variable ...
Thank you

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