[comp.dcom.fax] Gray scales in a fax card??

apb@cbnewsj.att.com (Amrit Bains) (12/23/90)

In connection with PC fax cards does anyone know if there is something
known as gray scales for the cards.

Amrit Bains
apb@cbnewsj.att.com

hrs1@cbnewsi.att.com (herman.r.silbiger) (12/23/90)

In article <1990Dec22.183648.13079@cbnewsj.att.com>, apb@cbnewsj.att.com (Amrit Bains) writes:
> 
> In connection with PC fax cards does anyone know if there is something
> known as gray scales for the cards.
> 
>

Many standalone fax terminals advertize that they provide up to 16 levels of
gray scale.  However, this is done by using the NSF (Non-Standard Facility) 
field, and is thus possible only if the called machine and calling machine
were made by tye same manufacturer, and both use the same option.

The topic of gray scale is under study in CCITT, and I expect that when a
suitable coding scheme is agreed on, it will be added to fax.

Herman Silbiger
reply to: hsilbiger@attmail.com
 

oeschi@netmbx.UUCP (Johann Deutinger) (12/24/90)

In article <1990Dec22.230350.1588@cbnewsi.att.com> hrs1@cbnewsi.att.com (herman.r.silbiger) writes:
>In article <1990Dec22.183648.13079@cbnewsj.att.com>, apb@cbnewsj.att.com (Amrit Bains) writes:
>> 
>> In connection with PC fax cards does anyone know if there is something
>> known as gray scales for the cards.
>
>Many standalone fax terminals advertize that they provide up to 16 levels of
>gray scale.  However, this is done by using the NSF (Non-Standard Facility) 
>field, and is thus possible only if the called machine and calling machine
>were made by tye same manufacturer, and both use the same option.
>
In my knowlegde many fax manufacturers say grey scale when they mean bi-level
sending of dithered images. This is not greyscaling but simulating the same
effect with more or less dense pixel areas. This lowers the resolution so
character oriented documents may suffer from this treatment too much.

It is compatible to all machines because it is still bi-level coding (black
and white pixels only). For fotos it is quite useful. Real greyscaling is
quite hard to do on a thermal printer. Dithering also takes much more
transmission time because there is a lot of white/black transitions which
is very bad for the usual modified huffman compression scheme.



-- 
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