how to make the background of an image transparent?

I'm having a bird image with white background..and i need to make the background transparent so that i can add it to a block of the sky image naturally. Can anyone please help me to do it in Matlab..Thanks in advance..

[Daniel Shub]

This might be related to this question or are you trying to take an image (say a png file), process it, and create a new image (also a png file)?

[Daniel Shub]

EDIT Moved answer to comments john-john said: how can we help or suggest you.. you didn't post your picture =)

Answer 1

[Image Analyst]

Extract color channels of each RGB image:

% Extract the individual red, green, and blue color channels.
redChannel = rgbBirdImage(:, :, 1);
greenChannel = rgbBirdImage(:, :, 2);
blueChannel = rgbBirdImage(:, :, 3);
skyRedChannel = rgbSkyImage(:, :, 1);
skyGreenChannel = rgbSkyImage(:, :, 2);
skyBlueChannel = rgbSkyImage(:, :, 3);

For each color channel, threshold

bird = greenChannel < threshold; % Create binary mask image.

Then do the replacement:

skyGreenChannel(bird) = greenChannel(bird); % Replace with bird pixels.

Then recombine:

compositeImage = cat(3, skyRedChannel, skyGreenChannel, skyBlueChannel);

Answer 2

[Walter Roberson]

Create a logical array BirdMask that is true for pixels that you want to continue to show, and false for background pixels. Display the sky image first. Then

image(BirdImage, 'AlphaData', BirdMask)

[Raseen Akhtar]

How would I get the logical array BirdMask?