[Image-SIG] float rgba list -> Image

Chris.Barker Chris.Barker at noaa.gov
Fri Sep 2 17:55:58 CEST 2011

On 9/2/11 12:33 AM, Ingo Randolf wrote:
> i get the RGBA-list from within blender...

ouch! I'm still amazed when folks write wrappers that use lists of 
numbers for large arrays of data -- it's simple NOT the way to go -- 
painfully slow and memory inefficient. This is what the PEP 3118 buffer 
protocol is for -- I know it's new, but I sure wish folks would use it.

Does Blender not provide a way to get some sort of efficient image 
object? in this case, you may even get better performance writing an 
image to file, and reading it back in with PIL.

> right now i have troubles getting numpy working in blenders bundled python (3.2)... so i could not try this proposal...

what was the problem? a simple "setup.py install" should work fine.

> making tuples out of the list (either with or without value-scaling) is too slow...

did you try making an array.array object? That's in the stdlib at least, 
though the scaling will be slower than numpy


> ingo
> Am 31.08.2011 um 20:51 schrieb Chris.Barker:
>> On 8/31/11 9:27 AM, Christoph Gohlke wrote:
>>> On 8/31/2011 7:21 AM, Ingo Randolf wrote:
>>>> I have a list with float-values describing an image like this:
>>>> [R, G, B, A, R, G, B, A, R, G, B, A, R, G, B, A, R, G, B, A, ... etc.]
>> I can't help but wonder why it's in that data structure to begin with -- as you've seen, it's a pretty painfully inefficient way to do it.
>>>> i played around with putdata...
>> you need it in a binary format that is compatible:
>>> Consider using numpy<http://numpy.scipy.org/>  and Image.fromarray.
>> this is probably the best way, but you can also use an array.array object -- create an array.array of type byte from your list, then pass that in to putdata. (details left as an exercise for the reader)
>> I think working with numbers in Python without numpy would be like working with text using lists of characters, rather than the string object.
>> -Chris
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Christopher Barker, Ph.D.

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