Creating a binary image with rgb values

I have to genarate a binary image of an ellipse having its inside as white while outside as black.But , the problem i am facing is that whenever the foreground and background of my input ellipse is either light or dark then the binary image becomes all black or all white.

[Adam Danz]

What function and parameter values are you using to create the binary image?

[aditya shrivastava]

redChannel = imag(:, :, 1);
greenChannel = imag(:, :, 2);
blueChannel = imag(:, :, 3);
maxGrayLevelR = max(redChannel(:));
minGrayLevelR = min(redChannel(:));
maxGrayLevelG = max(greenChannel(:));
minGrayLevelG = min(greenChannel(:));
maxGrayLevelB = max(blueChannel(:));
minGrayLevelB = min(blueChannel(:));
%Convert percentage threshold into an actual number.
thresholdLevelR = minGrayLevelR + 0.5*(maxGrayLevelR  - minGrayLevelR);
thresholdLevelG = minGrayLevelG + 0.5*(maxGrayLevelG  - minGrayLevelG);
thresholdLevelB = minGrayLevelB + 0.5*(maxGrayLevelB  - minGrayLevelB);

image_binary = redChannel  > (thresholdLevelR,thresholdLevelG,thresholdLevelB)/3;

image_binary = greenChannel  > max(thresholdLevelR,thresholdLevelG,thresholdLevelB)/3;

image_binary = blueChannel  > max(thresholdLevelR,thresholdLevelG,thresholdLevelB)/3;

[aditya shrivastava]

But ,it is not separating light background on light foregorund.

[Adam Danz]

Have you tried imbinarize()?

Explore the various methods and optional parameters.

[aditya shrivastava]

this function works very well.But, i specifically want the foreground of an image to be white and background to be black.So, i am using not(image) function. Is there any way by which i can know if the center pixel of the image is black or white. If it is white then i wont use not function .Otherwise,i will use not function.

[Adam Danz]

See my answer.

Answer 1

[Adam Danz]

Use imbinarize(). The output can be used to determine whether the center pixel is black (0) or white (1).

BW = imbinarize(. . .)
centerPixelValue = BW(round(size(BW,1)/2),(round(size(BW,2)/2)));