I'm not sure that this consumes enough cycles to warrant the additional
complexity of doing things differently on a per-backend basis (the
choice to stick with 8-bit colors would have to be made higher than the
backend to see any savings). The pcolor images are an exception, since
that code is common to all backends -- we can do whatever works best.
To see what the "upper limit" on the performance increase would be, I
modified draw_quad_mesh in the Agg backend so that it doesn't look up or
multiply colors at all (it just uses a hard-coded 8-bit black always),
and on the included pcolormesh benchmark, there was no significant
difference (I ran each 3 times, since the difference is so small):
trunk:
5.518 fps
5.530 fps
5.530 fps
trunk (hard-coded color):
5.507 fps
5.567 fps
5.302 fps
I did notice, however, that draw_quad_mesh makes an unnecessary
temporary buffer to convert the floating-point colors to 8-bit color.
Since each color is only converted once, it is slightly faster to do the
conversion on the fly and avoid the heap alloc/dealloc.
trunk (no alloc):
5.630 fps
5.618 fps
5.617 fps
Cheers,
Mike
Eric Firing wrote:
> Michael Droettboom wrote:
>> I think I'm a little confused by the question. From the Python
>> perspective, everything in the Agg backend takes floats. Agg
>> actually has color types for both floating point and 8-bit-per-plane
>> colors, though obviously it's converted to 8-bit-per-plane
>> eventually. But, of course, that is done on the fly without much
>> memory copying, so I'm quite surprised that the speed up is
>> significant... Where exactly is this conversion happening, and how
>> are you now avoiding it? (Is this in code that is not checked in,
>> perhaps?)
>
> I was referring to _image.cpp and the quadmesh code in _backend_agg.cpp.
> Both work directly with agg::rgba8, and can benefit from doing a color
> table lookup directly in 8-bit space instead of using floats and then
> converting.
>
> Eric
>
>>
>> As for the other backends, it's a mixed bag. PDF, PS and Cairo want
>> floats, SVG wants ints. Personally, I just *like* floats better, as
>> it feels more future proof, even though most people aren't using the
>> extra color resolution now. (Of course, if your plot relies on
>> high-resolution color, you probably need to rethink your plot
>> anyway... ;)
>>
>> Cheers, Mike
>
--
Michael Droettboom
Science Software Branch
Operations and Engineering Division
Space Telescope Science Institute
Operated by AURA for NASA
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