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Re: PDF Problem

From: Han-Wen Nienhuys
Subject: Re: PDF Problem
Date: Fri, 20 Jul 2007 11:39:27 -0700

2007/7/20, Rune Zedeler <address@hidden>:
You are right - the problem is not really related to this.
I still think that we should change to 1/72 inch instead if 1/72.27 inch
because this way all staff lines will have same distance on paper and on
screen, whereas with 1/72.27 it may seldomly happen that two staff lines

I don't understand this argument. We use exact distances everywhere,
and scale everything in 72/72.27 when we go through postscript.
Actually, lily uses mm internally, so there is still another factor.

Or are you suggesting that we drop 20pt staff and use 20.075pt staffs,
so it fits 72dpi displays better?

For generating the PNGs for the website/doc we use 101 dpi resolution,
which should put the staff lines at an integer number of pixels apart.

> I'm not very enthusiastic about a "optimize for screen" option.  I
> think that the sample image you posted looks horrid.

I agree. But this is how acroread renders pdf files.
I have attached three images.
The first is a screenshot of how a lilypond score looks in acroread

On linux, acroread has 'antialias' option, which changes the
rendering. Perhaps we can recommend people to use this option.

today, the second is a screenshot of how the same score would look with
screen optimization.
The third is a rendering in high resolution and afterwards scaled down.

The discussion of whether the third is better than the two first I start
But the discussion that is relevant here is whether the second (screen
optimized) image looks better than the first (what we have today in

> If you want to
> have certainty that images look like you want them to, you have to
> take control of the rendering process.

I agree, but that is not really possible in all cases.
I think it is a valid point to want to be able to produce pdfs that look
good in acroread - because acroread is what most people use.

My point is that we should not be doing black magic adjustments based
on unverified assumptions on how acrobat renders the page.

> That means that you should
> generate large (high DPI) PNG images and scale them down.

This is generally a bad idea when rendering text - because this way you
will not have any hinting information to generate the image.
(Hinting is the processing of an image to ensure that horizontal and
vertical lines are located on pixel boundaries).
If you turn off hinting you will get gray shadows along some of the
horizontal/vertical lines. On the 3rd attached image notice how the
stems are different. Some of them are thin and black while others are
thick, grey and blurry.

Yes, I know. IIRC we already do setstrokeadjust, which is the
instruction that should cause acrobat to use hinting for lines.

Han-Wen Nienhuys - address@hidden -

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