[Chimera-users] Representation of volume data in memory

Thomas Goddard goddard at cgl.ucsf.edu
Tue Jan 30 16:05:43 PST 2007

Hi Jeff,

I suspect 2-byte integers are not faster to access or compute with then 
4-byte floats on modern CPUs.  But more of the map will fit into the 
CPUs cache which could improve bandwidth and could make computing a 
contour surface faster.  But I don't think that will be significant. 
You would need to test it to know.  Chimera keeps the native data type 
of the map to conserve memory when reading large maps.


Jeff wrote:
> does this mean that a 2-byte integer format of a file will display 
> faster / render triangles faster than the equivalent sized 4-byte float 
> map?
> Thomas Goddard wrote:
>> Hi Jeff,
>>   Chimera keeps volume data in memory using the same numeric value 
>> types that are present in the file, for example, 32-bit float, 16-bit 
>> integer, 8-bit integer.
>>   Volume data is copied only when necessary -- for instance, using the 
>> Gaussian Filter tool creates a floating point copy of the data since 
>> Gaussian convolution of integer data produces a floating point result.
>>     Tom
>> Jeff wrote:
>>> does chimera store all values as float internally (even if the 
>>> original map is in 2 byte integers), making the mode of the MRC file 
>>> irrelevant to chimera's performance?
>>> -jeff

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