[Pythonmac-SIG] CoreGraphics, 10.5

[Erik van Blokland]

Folks,

I've been wrestling with some CoreGraphics stuff, OSX 10.5.2, stock  
Python 2.5.1. I want to load a RGB  image, then load a grayscale  
image, draw one while using the other as a mask. I can build all the  
required objects. I can draw with "masking-like things" happening to  
the image. But the masking appears to be according to a (random) piece  
of memory, rather than the pixels from the mask image.

The RGB image:
	 http://erik.letterror.com/cg/picture.png

The grayscale mask:
	 http://erik.letterror.com/cg/mask.tif

The resulting image:
	 http://erik.letterror.com/cg/results.png

The script:
	 http://erik.letterror.com/cg/cgMaskTestPost.py

The script which draws this file is below. Yellow background, rgb  
image of a neon sign, mask. I get the impression I'm somehow not  
making the right kind of mask. Or perhaps the parameters I'm passing  
to it are wrong. Perhaps the mask image is wrong. I've tried black/ 
white bitmaps, tiff, jpeg, png, grayscale 8 bit, 24 bit. Different  
formats result in different patterns being used as a mask - so there  
is some correlation between the file and the result. Is this anywhere  
close to how it needs to be done?

Any pointers are most welcome, thanks!

Erik van Blokland




#! /usr/bin/python2.5

from CoreGraphics import *
import os

def test():
	testWidth = 1000
	testHeight = 500
	fileName = 'picture.png'		# name of a 8 bit PNG, RGB image
	maskName = 'mask.tif'		# name of an 8 bit, grayscale tiff
	# the paths
	root = os.getcwd()
	filePath = os.path.join(root,fileName)
	maskPath = os.path.join(root,maskName)
	dstPath = os.path.join(root, "results.png")
	
	# data providers for the image and the mask
	img = CGImageImport(CGDataProviderCreateWithFilename(filePath))
	maskProvider = CGDataProviderCreateWithFilename(maskPath)
	imgMask = CGImageImport(maskProvider)
	
	# first, let's find out some things about the mask.
	width = imgMask.getWidth()
	height = imgMask.getHeight()
	bitsPerComponent = imgMask.getBitsPerComponent()
	bitsPerPixel = imgMask.getBitsPerPixel()
	bytesPerRow = imgMask.getBytesPerRow()	
	shouldInterpolate = True
	decode = [0,255]	# not relevant?
	# make the mask
	maskObject = CGImageMaskCreate(width, height,
		bitsPerComponent, bitsPerPixel,
		bytesPerRow, maskProvider,
		decode, shouldInterpolate)
	# now make the image with source image AND mask
	imgWithMask = CGImage_createWithMask(img, maskObject)
	# make a new image to save it all
	ctx = CGBitmapContextCreateWithColor(testWidth, testHeight,  
CGColorSpaceCreateDeviceRGB(), (0,0,0,0))
	# a background color
	ctx.setRGBFillColor(.9, .9, 0, .8)
	ctx.addRect(CGRectMake(0, 0, testWidth, testHeight))
	ctx.fillPath()
	# draw the masked image
	ctx.drawImage(CGRectMake(50, 50, width, height), imgWithMask)
	CGContext_writeToFile(ctx, dstPath, kCGImageFormatPNG)
	print "done"
	
if __name__ == "__main__":
	test()


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