Re: Weird Problem With CGImage
Re: Weird Problem With CGImage
- Subject: Re: Weird Problem With CGImage
- From: Jean-Daniel Dupas <email@hidden>
- Date: Fri, 25 Apr 2008 17:57:15 +0200
Using CGImageRef is not a realiable way to access pixel data of an
image.
You should create a CGBitmapContextCreate() instead and draw the part
you want in this context.
http://developer.apple.com/qa/qa2007/qa1509.html
Le 25 avr. 08 à 16:51, Carter R. Harrison a écrit :
This bug in my code has been driving me nuts for days, but I have
finally isolated the issue - only problem now is I don't understand
what I'm doing wrong.
I have a CGImage that I want to get the raw data bytes for. My code
is below:
CGImageRef sectionToCache =
CGImageCreateWithImageInRect(backingStore, CGRectMake(x, y, cx, cy));
NSLog(@"CGImage to cache has dimensions %d x %d and %d bytes per
row", CGImageGetWidth(sectionToCache),
CGImageGetHeight(sectionToCache),
CGImageGetBytesPerRow(sectionToCache));
CFDataRef dataRef =
CGDataProviderCopyData(CGImageGetDataProvider(sectionToCache));
NSLog(@"Length of cachedImage data: %d", CFDataGetLength(dataRef));
When the code runs, the log spits out the following:
CGImage to cache has dimensions 417 x 234 and 1668 bytes per row
Length of cachedImage data: 6672
What is killing me here is that the CGImage has dimensions 417x234
and 1668 bytes per row. That to me means that the CFDataRef that I
am obtaining should be 390,312 bytes (234 x 1668). But the
CFDataRef is only 6,672 bytes which is nowhere close to what I think
I should be getting. So I must be doing something wrong in trying
to get the bitmap data, but I'm not sure what else to do and I even
found some Apple docs with an example doing the exact same thing
that I am doing. Can anybody provide some insight on this? Thanks
everybody.
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