Re: [Openexr-devel] scanline order

[Florian Kainz]

Charles Henrich wrote:
> 
> > With ZIP and PIZ compression, pixels are stored in blocks of 16 or 32
> > scanlines, respectively.  With RLE and ZIPS compression, pixels are stored
> > in single-scanline blocks.
> 
> Anyway to alter this value in the writer to write in smaller chunks trading
> off compression for accessability?  32 scanlines seems like a rather huge
> chunk, especially for any "normal" size image?
> 
> -Crh
> 
>        Charles Henrich           Digital Domain          address@hidden
> 
>                          http://www.sigbus.com/~henrich

Hi Charles,

performance depends, of course, on the particular order in which
you are accessing an image's scanlines, but I would guess that
making the scan line blocks smaller would make reading the file 
slower, because seekg() would be called more often.  (When you 
call readpixels(), the probability that the scan line you want 
is in the block that is currently in memory, or in the next block
in the file, increases with the block size.)

Could you provide more details about what you are doing, so that
I can understand your problem better?

Florian