Weird issue with ofImage and masking

advanced
#1

I’m having a really strange issue, I think it has something to do with the way ofImage is set up loading an image or my lack of understanding it…

Basically I am masking an ofImage by using the following code:

  
  
//------------------------------------------------------------------  
void ofxAdvancedImage::mask(unsigned char * pixels, int w, int h) {  
	if(w*h <= width*height) {  
		setImageType(OF_IMAGE_COLOR_ALPHA);  
		  
		for(int i=0; i<width*height;i++) {  
			int thisAlphaPixel=(i*4)+3;  
			myPixels.pixels[thisAlphaPixel] = pixels[i];  
		}  
		  
		//Load the blurred image in  
		if (myPixels.bAllocated == true && bUseTexture == true){  
			tex.loadData(myPixels.pixels, myPixels.width, myPixels.height, myPixels.glDataType);  
		}  
	} else {  
		cout<< "Image is too big to be a mask!" <<endl;  
	}  
}

which I pass in an array of grayscale pixels to use as a mask. Basically if I load in an RGB image and run this code nothing happens. If I change int thisAlphaPixel=(i*4)+3 toint thisAlphaPixel=(i*4) or int thisAlphaPixel=(i*4)+2 or int thisAlphaPixel=(i*4)+1 it will successfully mask that color channel (R,G,B).

So I’m thinking…yea this should work but its not, maybe something I’m doing wrong. Then the bizarreness starts…if I load in a Transparent PNG to my ofImage…it works perfectly fine. This is the only way it works.

I have tried setting the image type before and after loading the image of OF_IMAGE_COLOR (GL_RGBA) as well as the call in the code before applying the changes to the alpha pixels, but nothing works unless the image loaded in originally has an alpha channel.

I feel like something with the way freeImage is being used is preventing the alpha channel from being used when a non-alpha image is loaded in.

Any help would be greatly appreciated!

Thanks to anyone who can help,
-Steve

#2

I think it’s a bug with ofImage – follow where “tex.allocate()” happens, as this sets up the internal data type of the texture – I’d be it’s being set as color, and even though you are uploading alpha data, it’s not going to display it.

(ie, tex.loadData doesn’t change the “internal” representation of the data).

it looks like we need to do some reallocation of the texture if you change the image type. We actually almost always used it to alter the pixels array :wink: so this is the first time we’ve seen it used like that…

take care,
zach