Re: [Bug 688243] Spurious lines between joined filled rectangles and antialiasing (fwd)

[Daniel J S. <dan...@ie...>]

Petr,

My somewhat limited experience with ghostscript was disappointing.  I appreciate what it does, but it seems less than elegant.  I looked at some of the PostScript code it generates when translating and it appeared bloated in a major way.

I've seen this before with some of your demo examples.  It bewildered me.  Not only were the white lines present, but the color scheme was incorrect for a large percentage of the parallelograms.  But I thought it was fixed since I no longer saw the effect in ghostview after I upgraded to Fedora 3.

This doesn't seem like a problem that should exist as it is described below in the manual.  It sounds to me like it has something to do with the lowpass filter kernel used to rid aliasing.  Perhaps it was originally written to render in a way that stuck them in a corner without a lot of rewrite.

> I'm asking about how to switch GraphicsAlphaBits from within the ps code...

I'd be careful to not add such a thing *unless* it is standard PostScript.

Dan


Petr Mikulik wrote:
> Below is a answer to the bug report by ghostscript people. The 
> referenced bug 687742 refers to ghostscript documentation, where, 
> amazingly, you can read the following:
> 
> -dTextAlphaBits=n
> -dGraphicsAlphaBits=n
>     These options control the use of subsample antialiasing. Their use 
> is highly recommended for producing high quality rasterizations. The 
> subsampling box size n should be 4 for optimum output, but smaller 
> values can be used for faster rendering. Antialiasing is enabled 
> separately for text and graphics content. Allowed values are 1, 2 or 4.
> 
>     Note that because of the way antialiasing blends the edges of shapes 
> into the background when they are drawn some files that rely on joining 
> separate filled polygons together to cover an area may not render as 
> expected with GraphicsAlphaBits at 2 or 4. If you encounter strange 
> lines within solid areas, try rendering that file again with 
> -dGraphicsAlphaBits=1.
> 
> I'm asking about how to switch GraphicsAlphaBits from within the ps code...
> 
> 
> ---------- Forwarded message ----------
> Date: Wed, 27 Jul 2005 13:10:25 -0700 (PDT)
> From: bug...@gh...
> Subject: [Bug 688243] Spurious lines between joined filled rectangles and
>     antialiasing
> 
> http://bugs.ghostscript.com/show_bug.cgi?id=688243
> 
> ------- Additional Comments From ale...@co...  2005-07-27 13:10 
> -------
> Created an attachment (id=1578)
>  --> (http://bugs.ghostscript.com/attachment.cgi?id=1578&action=view)
> foo.ps -- modified sample
> 
> This is an old and rather difficult to fix issue. See the bug 687742 for 
> the
> discussion. gnuplot can try to write adjacent boxes in the single fill
> operation but this is not possible when the bxes have different colors.
> See the modified sample file.
> 
> 
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