Re: Problem with converting an NSImage to grayscale
Re: Problem with converting an NSImage to grayscale
- Subject: Re: Problem with converting an NSImage to grayscale
- From: "John C. Randolph" <email@hidden>
- Date: Tue, 30 Aug 2005 07:31:56 -0700
On Aug 30, 2005, at 6:44 AM, Heinrich Giesen wrote:
On 30.08.2005, at 13:06, Arik Devens wrote:
I'm trying to write some code to covert arbitrary RGB and RGBA
NSImage's
to grayscale. I've written a routine, which started out as the
negative
image sample from ImageDifference but I'm running into some odd
problems.
The code works on some images and not others, but I haven't been
able to
figure out why some work and some don't.
John C. Randolph answered:
I wrote the Image Difference sample, and the code I have in there to
dig through the pixel data is no longer necessary. Just use the
monochrome filter from CoreImage. It will be much faster, since the
processing will happen on the GPU.
Maybe that the monochrom filter from CoreImage is faster but it
does not
explain why Ariks code doen't work. Simple answer: his code
(clearly influenced
from the ImageDifference code) is wrong because the ImageDifference
code
is wrong, especially this "digging through the imaga data".
The Image Difference sample is correct, for versions of OS X prior to
Tiger. The point I was making is that it's no longer necessary to do
this at all, since CoreImage has a filter that does the RGB to
grayscale mapping according to the NTSC formula.
-jcr
John C. Randolph <email@hidden> (408) 914-0013
Roaming Cocoa Engineer,
Available for your projects at great Expense and Inconvenience.
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