[ome-users] Incomplete colormap with getXBitLookupTable() method.

[Melissa Linkert]

Hi Stéphane,

[CC'ing the ome-users mailing list]

> When i open a GIF file with transparent background i can't recover
> the alpha information from the colormap value with
> get8BitLookupTable() method as it returns only RGB colormap and not
> RGBA ones. Is there any plans of providing RGBA colormap information
> in future ?

The current behavior is correct.  GIF files do not contain alpha information;
see the color table definition (section 19) in:

http://www.w3.org/Graphics/GIF/spec-gif89a.txt

> Also i wanted to know if there some way to know if the 4th channel
> of a TIF image basically contains alpha data or color data ? Thanks.

The presence of a non-zero "ExtraSamples" entry in the metadata table
generally indicates that the last channel is an alpha channel.
Bio-Formats itself doesn't make any distinction between alpha and
non-alpha data.

Regards,
-Melissa

On Thu, Apr 11, 2013 at 12:09:19PM +0200, Stéphane Dallongeville wrote:
> Hi Melissa,
> 
> When i open a GIF file with transparent background i can't recover
> the alpha information from the colormap value with
> get8BitLookupTable() method as it returns only RGB colormap and not
> RGBA ones. Is there any plans of providing RGBA colormap information
> in future ?
> Also i wanted to know if there some way to know if the 4th channel
> of a TIF image basically contains alpha data or color data ? Thanks.
> 
> Best regards,
> 
> -- 
> Stephane Dallongeville
> Unité d'Analyse d'Images Quantitative
> CNRS URA 2582
> Institut Pasteur
> 25 rue du Dr Roux - 75015 Paris - France
> 
> Tel: +33 (0)1 45 68 87 01
> Fax: +33 (0)1 40 61 33 30
> 
> http://www.bioimageanalysis.org/
>