AWARE [SYSTEMS] Imaging expertise for the Delphi developer
AWare Systems, Imaging expertise for the Delphi developer, Home TIFF and LibTiff Mailing List Archive

LibTiff Mailing List

TIFF and LibTiff Mailing List Archive
May 1997

Previous Thread
Next Thread

Previous by Thread
Next by Thread

Previous by Date
Next by Date

Contact

The TIFF Mailing List Homepage
This list is run by Frank Warmerdam
Archive maintained by AWare Systems



Valid HTML 4.01!



Thread

1997.05.09 15:27 "To ALL TIFF MAILING LIST MEMBERS", by Sanjay G Prabhudesai
1997.05.12 05:44 "Re: To ALL TIFF MAILING LIST MEMBERS", by Rainer Wiesenfarth

1997.05.09 15:27 "To ALL TIFF MAILING LIST MEMBERS", by Sanjay G Prabhudesai

Hello Everybody,

Let me first apologise to all of you for not expressing myself clearly in
my mail I sent yesterday on "Group 4 compression and 256 Colors".

Prior to yesterday's mail, I had sent another mail seeking your expert
advise on suitability of using Group 4 compression for 256 colour images. I
got very educative responses from different people. Once again I thank all
of them for the help.

All the mails clearly indicated that it is not advisable to apply Group 4
compression for colour images as it could lead to expansion instead of
compression. I also recieved explanation for why it happens that way. All
the mails pointed to available alternatives. 

I have a customer who is bent on using Group 4 compression for reasons not
known to me. One of the responses I received a few days ago, indicated the
possibility of using the Group 4 compression with 256 colours, although it
would expand the image rather than compress. The following method was
suggested :

   Treat a 256 color palette image as a "bilevel" image       (multiplying
image width by 8 before applying group 4       compression) 

I was trying this approach. I wanted to figure out if TIFF files generated
in this manner could be understood by other readers available in the
market. I hoped to gain more insight, from this experiment, on the basis of
which I could further disscuss this matter with the customer.

While trying this approach using libTIFF writer I got the following error
message:

 "Bits per sample must be 1 for Group 3/4 encoding/decoding".

I could not figure out how to overcome this problem. Hence I posted another
mail. Unfortunately I did not express myself clearly in that mail.

Once again, I sincerely apologise for not expressing myself clearly and the
inconvenience caused to all of you. I thank you very much for all the
responses and being patient with me.

Regards,

Sanjay Prabhudesai