Re: [Openexr-user] Details in PIZ compression

[Jack Mak]

Hi Florian,

Thanks for your explanation. I got the big picture. Before I look through the source code, just wonder, are there any documents (papers, standards...) give a detailed description of PIZ compression?

Best regards,

Jack

On Fri, Feb 22, 2008 at 2:39 PM, Florian Kainz <address@hidden> wrote:

For the details of PIZ compression, you'll have to
look at the source code, but here's a brief overview:

The image is split into blocks that are 32 pixels high
and as wide as the image.  The blocks are split into
individual channels.  The bit-patterns that comprise
the half values in each block are re-interpreted as
16-bit integers, and the integers are run through a
lookup table that shapes their distribution such that
comb-like histograms, with spikes separated by wide
gaps, are avoided.  A Haar wavelet transform is applied
to the output of the lookup table, and the output of
the wavelet transform is compacted using a 16-bit
Huffman coder.

PIZ is mathematically lossless because each individual
step is reversible.  The wavelet transform is reversible
because it operates on integers and has no roundoff error.

Florian

Jack Mak wrote:
> Hi Experts,
>
> How does the PIZ compression work? Where can I find reference that
> discusses it in detail? (I checked out the documentations on the
> OpenEXR website, but they does not help.)
>
> Many thanks
>
> Jack
>
>

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