How to change a pixel value of a RGB

I am trying to change a pixel value of a RGB image with the property '512*512*3 double'. I tried like gray scale images below

imagename(100,100) = [0.1,0.1,0.1];

or

imagename(100,100,1) = 1.0;

iamgename(100,100,2) = 0.1;

imagename(100,100,3) = 0.1;

The first one results more than original dimensions.. I have spent hours and so tried now.

The second one results redish image......

I'd be very appreciate with any help. Thanks.

Answer 1

[José-Luis]

 imagename(100,100,:) = [0.1, 0.1, 0.1];

Please read about indexing.

Answer 2

[Image Analyst]

Not sure what you're asking, but as you found out, the second way is correct. A color RGB image is a 3-D array with one color channel for red, one for green, and one for blue. Each color channel by itself is a 2-D image but when combined into an RGB image it becomes a 3-D array which takes 3 indexes, (row, column, colorChannelValue). To set a particular row and column to a value you have to use : and specify all three values

rgbImage(row, column, :) = [redValue, greenValue, blueValue];

Or you can do it one color channel at a time.

rgbImage(row, column, 1) = redValue;
rgbImage(row, column, 2) = greenValue;
rgbImage(row, column, 3) = blueValue;

But you can't do it like you did at first.