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Re: Bitmap objects


From: Willem Rein Oudshoorn
Subject: Re: Bitmap objects
Date: 29 Jan 2002 08:33:24 +0100
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.1

Pete French <address@hidden> writes:
> 
> Thats the conclusion I came to in the end. Almost all the bits are there, you
> just need to re-build the _bitmap_combine_alpha function (carefully) to
> use them all.
> 
> Thanks for the copy of the documentation for DPSimage by the way, most useful.
> I dont think I ahve that anywhere - got the "purple book" but it
> doesnt seem to be doumented in there. I have the red book too whhich I can
> take a look at as well.

The documentation for the postscript operator image is to be found in the
red book (Section 4.10)
> 
> On the other hane the argumenst to DPSimage do seem to be missing a couple
> of fairly vital parameters. One is the number of bytes per row. 

Actually that is not missing.  The data sources should
be considered as a continuous bitstream with highorder bits first.
However, every row of te source image starts at a character boundary.

> either. Does xgps support somewhere a "current colourspace" that can
> be read ? I havent noticed anything, and certainly the image objecst
> do not seem to set any colourspace before trying to draw themselves.

First of all, I do not think that the colourspace is a paramater
to the image operators.
Second, I can't remember seeing a colourspace in the xgps backend
at all.

However, the image dictionary actually has a required parameter
`Decode' which is an array and contains 2 values per (colour) component.

These values specify the minimum and maximum value of this colour component
and the values from the data source should be mapped in to this 
range.
 
> PS: is the general feeling that bitmaps should be displayed as speedily as
>     possible, or is a certain amoount of speed worth trading for a more
>     faithful rendering of the original ?

There is the parameter `Interpolate' that defaults to false
which might be used to switch between fast / faithfull.

Wim Oudshoorn.

P.S.: Sorry, I forgot to read section 4.10 so I missed 
the Decode and Interpolate parameters in my first mail.



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