Re: [boost] GIL Review

From: Matt Gruenke (mgruenke_at_[hidden])
Date: 2006-11-02 20:13:49

Fernando Cacciola wrote:

>Matt Gruenke wrote:
>  
>
>>Fernando Cacciola wrote:
>>
>>    
>>
>>>Now, off the pixel/color topic.
>>>rom the Quicktime format disccusion: is it possible to supersample
>>>(rather than subsample) an image? That is, to take two or more
>>>consequtive pixels in a row and pretend is just one pixel?
>>>
>>>      
>>>
>>You're talking about a subsampling (or decimating) iterator,
>>    
>>
>
>No, but I can see how the way I expressed it looked like that.
>
>  
>
>>instead-
>>of
>>an interpolating iterator?
>>    
>>
>
>Exactly. The idea was not to skip even or odd pixels (which subsampling 
>does) but to combine them.
>  
>

You mean like a 4:2:2 iterator, which contains two consecutive luma 
samples and a chroma sample (pair)?  Perhaps you could generalize this 
into a multisample iterator, and provided a means of getting the image 
dimensions in terms of multisample steps.  However, I'm not sure how 
useful any of that would be.

>>However, for most purposes where this is desirable, it is probably
>>more efficient to write a routine that resamples entire rows and
>>columns at a time.
>>    
>>
>
>Which is what Ulrich said. It would be interesting the benchmark it though.
>  
>

It would probably be slower, because it would involve redundant channel 
unpacking (certainly, if you're using a large reconstruction kernel) and 
probably redundant loads of reconstruction kernel coefficients.

Matt