Re: Weird Problem With CGImage

FROM : Jean-Daniel Dupas
DATE : Fri Apr 25 20:45:47 2008

Le 25 avr. 08 à 18:12, David Duncan a écrit :

> On Apr 25, 2008, at 7:51 AM, Carter R. Harrison wrote:
>

>> 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.

>
> This seems to be related to the CGImageCreateWithImageInRect() call, 
> but I can't imagine why. CGDataProviderCopyData() seems to work 
> perfectly with an original image in my limited testing, so please 
> file a bug (and let me know what the bug number is).
>


I didn't find any documentation about CGDataProviderCopyData() except 
this comment in the header:

/* Return a copy of the data specified by provider. Returns NULL if a
  * complete copy of the data can't be obtained (for example, if the
  * underlying data is too large to fit in memory). */

What is the expected output format of the data it returns ?