How do i scan pixel from an rgb image and then if red value is higher than 200 show red only and if its lower = all 3 colors = 0

Answer 1

[David Fletcher]

May not be the best answer - I don't do much image manipulation work

%load and display image
imageData=imread('test.jpeg');
subplot(2,1,1)
imshow(imageData);

%Create mask for red colour data >200
redMask=imageData(:,:,1)>200;

%Apply mask to red channel
red=imageData(:,:,1);
red=red.*cast(redMask,'like',imageData);

%Clear colour data from all channels
imageData=imageData*0;
%Replace red channel with the masked data
imageData(:,:,1)=red;
%Show image with red channel mask mask
subplot(2,1,2)
imshow(imageData);

[Moe Makki]

I need using for loops please .

[David Fletcher]

It is fairly easy to convert this to a for loop solution (or even two for loops), but you should give it a go yourself - after all that is the whole purpose of homework. You will gain nothing by just being handed a solution. Set up two for loops to iterate through the pixels on a colour plane (pixels on the other two colour planes can be checked and adjusted at the same time). Check back if you have problems.

[Moe Makki]

@David Fletcher

originalImage = imread('Colors.jpg');

[rows, columns, numberOfColorChannels] = size(originalImage);

if numberOfColorChannels == 3

for column = 1 : columns

for row = 1 : rows

redValue = originalImage(row, column, 1);

greenValue = originalImage(row, column, 2);

blueValue = originalImage(row, column, 3);

if redValue>200

redValue=255;

greenValue=0;

BlueValue=0;

else if redValue<200

redValue=0;

greenValue=0

BlueValue=0

end

end

end

end

end

imshow('Colors.jpg');

[Moe Makki]

what is wrong in this code

[David Fletcher]

Good try. Just a few things - there is no point in getting the value of pixels in the green and blue layers: they are of no interest, they do not need to be checked. The if statement for checking the red value doesn't need an extra else if clause: either the red value is over 200 or it isn't - there is only need for an if else to cover both situations. When you are assigning colour values, you need to apply them to the image pixels, not to the variables you have assigned to check the values of the pixels. Try this

originalImage = imread('Colors.jpg');
[rows, columns, numberOfColorChannels] = size(originalImage);
if numberOfColorChannels == 3
  
  for column = 1 : columns
    for row = 1 : rows
      redValue = originalImage(row, column, 1);
     
        if redValue>200
            originalImage(row, column, 1)=255;
            originalImage(row, column, 2:3)=0;
        else
            originalImage(row, column, 1:3)=0;
        end
    end
  end
end

imshow(originalImage);

[Moe Makki]

@David Fletcher Thanks for making it clearer

but the output is still the same image

blue and green colors are still there

is it because of the if statement ?

in the workspace i can see the redValue=35

which means the (else) statement should work = all colors = 0 = black image

it still shows the normal image

what do you think is the problem here

[Moe Makki]

[David Fletcher]

Is this still your code, or the code I put down above? When I run my amended code on the image I get the results shown above (which is I believe what you want).

[Moe Makki]

oops my bad there was an error with imshow i replaced it with the same picture

[Moe Makki]

Thanks for your help appreciated.

Answer 2

[Image Analyst]

Try this:

% Find where red value is more than 200.
mask = rgbImage(:, :, 1) > 200;
% Mask the image using bsxfun() function to multiply the mask by each channel individually.
maskedRgbImage = bsxfun(@times, rgbImage, cast(mask, 'like', rgbImage));

[Moe Makki]

@Image Analyst it is possible to use two for loops and if yes how please ? thanks for your answers

[Moe Makki]

originalImage = imread('Colors.jpg');

[rows, columns, numberOfColorChannels] = size(originalImage);

if numberOfColorChannels == 3

for column = 1 : columns

for row = 1 : rows

redValue = originalImage(row, column, 1);

greenValue = originalImage(row, column, 2);

blueValue = originalImage(row, column, 3);

if redValue>200

redValue=255;

greenValue=0;

BlueValue=0;

else if redValue<200

redValue=0;

greenValue=0

BlueValue=0

end

end

end

end

end

imshow('Colors.jpg');

[Image Analyst]

@Moe Makki, Yes, but why would you want to do it that less efficient way? The best answer is the two line snippet I gave you.

[Moe Makki]

@Image Analyst sadly the instructor asked to do it in double for loops . it's not my own choice

[Image Analyst]

In the future, please "Tag" the post as homework if it's homework (I've done it for you now). That tells us not to post full working code, that, if you turn in as your own, may get you into trouble for plagiarism. We wouldn't want you to get into trouble.

[Moe Makki]

@Image Analyst will do thanks for your lovely advice .

Have a great day sir.