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From Peter Becker <pbec...@dstc.edu.au>
Subject Re: Text rendering changes after upgrade to 1.5
Date Thu, 11 Sep 2003 01:10:19 GMT
Thomas DeWeese wrote:

> Peter Becker wrote:
>
>> Hi all,
>>
>> after someone reported having troubles with my little XWeb program 
>> (http://xweb.sf.net) and rendering SVGs on a 1.4.2 JDK on Linux, I 
>> tried upgrading to Batik 1.5. This seems to fix the problem with 
>> empty results which were reported, but unfortunately the looks of 
>> some buttons rendered for one of my sites (http://tockit.sf.net) 
>> change quite a bit.
>>
>> Since I added the Batik version to XWeb before I figured out that one 
>> should keep track of version numbers I can't tell the version of 
>> Batik I used before -- according to CVS it must be about 17 month 
>> old. Here are some comparisons of PNGs rendered with that Batik, with 
>> Batik 1.5 and the SVG used to create them (kind of -- it is what XWeb 
>> would generate). Total file size is less than 11kb.
>>
>> Example one:
>> - http://www.itee.uq.edu.au/~pbecker/batik/overview_old.png
>> - http://www.itee.uq.edu.au/~pbecker/batik/overview_1_5.png
>> - http://www.itee.uq.edu.au/~pbecker/batik/overview.svg
>>
>> This one looks pretty much the same to the old version in Adobe's 
>> viewer.
>>
>> Example two:
>> - http://www.itee.uq.edu.au/~pbecker/batik/docco_old.png
>> - http://www.itee.uq.edu.au/~pbecker/batik/docco_1_5.png
>> - http://www.itee.uq.edu.au/~pbecker/batik/docco.svg
>>
>> This SVG actually could be better -- at least Adobe's viewer doesn't 
>> really like it.
>>
>> Any explanation for this problem? Anything I can do to avoid it? If 
>> it is a bug -- any hints were to dig in the code?
>
>
>   The problem is caused by our switching to use drawGlyphVector in many
> cases instead of always drawing raw shapes.  Fortunately you can override
> this by saying text-rendering="GeometricPrecision".  This should give
> you the same rendering as before.  You might also try 
> 'optimizeLegability"
> which will shut off anti-aliasing of the text - some people prefer it. 

I don't understand this bit. You changed the code somehow and now the 
text looks quite different. Is this a feature? Or a bug? Is there any 
specification how the text should look like? The thing I found is this 
entry:

  http://www.w3.org/TR/SVG11/painting.html#TextRenderingProperty

which says that the default setting "auto" ... "Indicates that the user 
agent shall make appropriate tradeoffs to balance speed, legibility and 
geometric precision, but with legibility given more importance than 
speed and geometric precision."

So I assume that you changed the tradeoff policy between the Batik 
versions. But I must say that I disagree with the choice -- for the 
purpose of offline-rendering speed doesn't really bother me that much. 
Is there any way that I can set the behaviour for "auto" from the Java 
side of things? I want my Java program to prefer precision over speed 
for any SVG given to it.

>> BTW: it still seems the gamma problem I have is still around. If you 
>> look at http://tockit.sf.net with Internet Explorer you will notice 
>> that the navigation PNGs are of a slightly different colour than the 
>> surrounding bits and pieces. I tracked that down once to the gamma 
>> value in the PNGs which seems to be ignored by most software but IE 
>> (e.g. the site looks good in Mozilla). Is there any new insight on 
>> how to avoid that problem?
>
>
>   From what you have said so far I would say it is a bug in what ever
> other software you used to generate PNG files that they do not include
> a gama chunk.  You could hack Batik so it doesn't generate one but I
> don't think this would be the right approach to take. 

Hmmm... look at this page in IE: 
http://www.itee.uq.edu.au/~pbecker/batik/testColor.html

This is the Batik-rendered PNG on top of HTML background with exactly 
the same RGB values. And it is clearly rendered differently while 
Mozilla produces the same color. As does Adobe's viewer from the SVG.

According to IrfanView the color rendered by IE on screen is 
(76,106,148) instead of the (90,115,156) it should be. I don't have any 
of these problems with other PNGs -- at least I didn't notice although I 
tend to be picky about matching up colors.

But let's not play the blame game -- I don't care whose fault it is, I 
just want the results to be good. At the moment I am not happy with the 
looks of my website in IE -- which I rarely see myself but unfortunately 
IE is still the most common browser, so I have to accomodate for that. 
It seems to be somehow the combination of Batik's rendering of the SVG 
into PNG with IE's rendering of the PNG onto the screen that causes the 
problem -- most programs I tried display the PNG as I want it.

Cheers,
  Peter


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