[fitsbits] reopening of Public Comment Period on the compression conventions

[William Pence]

When using algorithms like PLIO or Rice, which are designed to 
efficiently compress data masks containing a pixel array of ones and 
zeros, it makes no difference what integer data type one uses to 
represent the mask.  The compressed masks will have exactly the same 
size, regardless of the original mask data type. This is because these 
algorithms effectively just record the location of the non-zero pixels, 
so how one represents those non-zero pixels (as a bit, byte, or longer 
integer word) has no effect.

The main reason that support for the NULL_PIXEL_MASK option has not 
(yet) been implemented in CFITSIO is that there are not many use cases 
where this capability is needed.  Given the current set of supported 
compression algorithms, the only time it might be useful is when using 
the H-Compress algorithm in it's lossy compression mode to achieve a 
high degree of compression of integer images (typically with compression 
ratios of 10 to 100).  However, these highly compressed images are 
typically only used to provide a 'quick look' preview of the image, and 
it would be ill-advised to try to do any quantitative analysis on such 
images.  Therefore, there is not much need to exactly preserve the 
location of any null pixels in such highly degraded images.

-Bill

On 1/13/2016 12:48 AM, van Nieuwenhoven, Richard wrote:
> Just a small note to NULL_PIXEL_MASK, it not yet used (shouldn't be
> because there are no implementations available as Bill has not
> implemented it yet). I think it is a waste of space using a byte for
> every pixel to indicate if it is null or not, even if it is compressed
> afterwards. Could it not be seen an array of bits, still compressed
> because most values would be the set. The size of the array would
> indicate that a bit mask was used, so no additional information is
> necessary.
>
> -Ritchie
>
>
>
> Am 2016-01-11 um 15:36 schrieb Lucio Chiappetti:
>> ANNOUNCEMENT:  START OF FORMAL PUBLIC COMMENT PERIOD
>>
>> This is to announce the official reopening of a formal Public Comment
>> Period on the incorporation of the Tiled Image Compression and Tiled
>> Table Compression conventions in the FITS Standard.
>>
>> A previous PCP was held in June-July (started on 16 Jun 2015).
>>
>> We are now re-opening the Public Comment Period to collect comments on
>> the modified text, ONE CONVENTION AT A TIME. When the PCP is over,
>> IAUFWG will vote on one convention in turn, while the next one will be
>> offered for public comments, and so on.
>>
>> The second convention if the list, to be discussed NOW defines the
>> Tiled Image Compression and Tiled Table Compression conventions.
>>
>> The proposed text consists
>>
>> - in the ADDITION of an entire new chapter (10)  to the FITS Standard
>>    Document which describes the two conventions in a common prescriptive
>>    framework.
>> - It also includes the ADDITION of a new non-prescriptive Appendix I,
>>
>> Only minor re-wording were applied w.r.t. the earlier version.
>> Considering that, despite its complexity, the proposal did not receive
>> any substantial objections, I am reopening the PCP for TWO WEEKS (in
>> order to speed up the cumulative prcoess dealing with all conventions),
>> but this can be extended if requested and motivated.
>>
>> The updated draft text is available at
>> http://sax.iasf-milano.inaf.it/~lucio/FITS/Conventions/compression-rev.pdf
>>
>> - the relevant bibliographic references, and appendices C and H.3 will be
>>    updated accordingly at the end of the convention incorporation procedure
>>    (this text is NOT shown but a cumulative draft is available at
>>    http://sax.iasf-milano.inaf.it/~lucio/FITS/Conventions/commonapps-rev.pdf
>>
>> Please review the text carefully and post any comments, criticisms, or
>> suggestions on the FITSBITS mailing list.
>>
>> Supporting material for the PREVIOUS public comment period announcement
>> can be retrieved from the FITSBITS archives
>> https://listmgr.nrao.edu/pipermail/fitsbits/2015-June/002615.html
>>
>> ==================================================================
>>
>> The reopened Public Comment Period starts today 11 January 2015 and will
>> last until 24 January 2016, unless extensions are requested and motivated.
>>
>
>

-- 
____________________________________________________________________
Dr. William Pence    Astrophysicist     William.Pence at nasa.gov
NASA/GSFC Code 662     [Emeritus]       +1-301-286-4599 (voice)
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