Cut out video image by setting pixels alpha?

@Gallo wrote:

hello,

My purpose is to use a kinect to grab an RGB image. And from the depth image, create a mask to keep only an object on the front.

i really don't know how to achieve this but here is the solution that seems logical to me :

From the depth image i apply some threshold and use it to change the alpha of the RGB image... i hope i am making myself clear here... but the purpose here is to make some pixels transparent (basically the background) and keep only the object on the front.

// update()
if (kinect.isFrameNew()) {
    ofPixels depthImage;
    depthImage = kinect.getDepthPixels();

    kinectRGB = kinect.getPixels();

    for (int y = 0; y < depthImage.getHeight(); y++) {
        for (int x = 0; x < depthImage.getWidth(); x++) {
            ofColor c = depthImage.getColor(x, y);
            if (c.getBrightness() > nearClip && c.getBrightness() < farClip) {
                ofColor newColor(kinectRGB.getColor(x, y));
                newColor.a = 255;
                kinectRGB.setColor(x, y, newColor);
            }
            else {
                ofColor newColor(kinectRGB.getColor(x, y));
                newColor.a = 0;
                kinectRGB.setColor(x, y, newColor);
            }
        }
    }
    kinectRGB.update();
}

then

   // draw()
   compo.begin();
   kinectRGB.draw(0, 0);
   compo.end();

where

// compo is an FBO
compo.allocate(640, 480, GL_RGBA);
compo.begin();
ofClear(0);
compo.end();

// kinectRGB is an ofImage
kinectRGB.allocate(640, 480, OF_IMAGE_COLOR_ALPHA);

it doesn't seem to work, i only end up with the full RGB image...

Is it the good way to go ?

Does setting alpha for pixels creates image transparency ?

thanks a lot

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