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

[Stéphane Dallongeville]

Hi Melissa,

Thanks for your reply. By alpha information i meant complete transparent 
color, in GIF you can define a specific color index to be transparent 
(defined in section 23.c.viii). I attached an example GIF file with a 
transparent background.
I was expecting an alpha entry set to 0 for the transparent color index 
(and 255 for the others) but maybe there is an other way to retrieve 
this information from Bio-Formats ?
Thanks for the "ExtraSamples" metadata tip, i will try to use it :)

Best Regards,

- Stephane


Le 11/04/2013 22:40, Melissa Linkert a écrit :
> 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/
>>


-- 
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/

-------------- next part --------------
A non-text attachment was scrubbed...
Name: Klocka_transparent.GIF
Type: image/gif
Size: 55800 bytes
Desc: not available
URL: <http://lists.openmicroscopy.org.uk/pipermail/ome-users/attachments/20130412/513ed1b0/attachment.gif>