Why doesn't 100% zoom in Adobe Reader draw things at the correct size?

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5 total messages Started by Chris Shearer Cooper Thu, 30 Sep 2010 15:23

Author: Chris Shearer Cooper
Date: Thu, 30 Sep 2010 15:23

23 lines
2139 bytes

I have a very simple PDF file that changes the effective resolution
from 72 dpi to 96 dpi (and the origin from bottom-left to top-left)
and then draws a line 96 units long:

        q 0.750000 0 0 0.750000 0.000000 1456.500000 cm

        q 1.000000 -0.000000 -0.000000 1.000000 48.000000 -48.000000
cm
        0.0 0.0 1.0 RG 1 w 1 J 100 -125 m 196 -125 l S Q

        Q

The line is 96 units long, apply the transformation and it should be
72 units long in the default coordinate system, which would be exactly
1 inch.

But when I view this PDF in Adobe Reader 8 on my screen (Windows XP)
at 100% zoom, the resulting line is almost 1.25" long.

Wassup?

Thanks,
Chris

Re: Why doesn't 100% zoom in Adobe Reader draw things at the correct size?

Author: bugbear
Date: Thu, 30 Sep 2010 15:59

31 lines
2800 bytes

Chris Shearer Cooper wrote:
> I have a very simple PDF file that changes the effective resolution
> from 72 dpi to 96 dpi (and the origin from bottom-left to top-left)
> and then draws a line 96 units long:
> 
>         q 0.750000 0 0 0.750000 0.000000 1456.500000 cm
> 
>         q 1.000000 -0.000000 -0.000000 1.000000 48.000000 -48.000000
> cm
>         0.0 0.0 1.0 RG 1 w 1 J 100 -125 m 196 -125 l S Q
> 
>         Q
> 
> The line is 96 units long, apply the transformation and it should be
> 72 units long in the default coordinate system, which would be exactly
> 1 inch.
> 
> But when I view this PDF in Adobe Reader 8 on my screen (Windows XP)
> at 100% zoom, the resulting line is almost 1.25" long.
> 
> Wassup?

Use a longer line. to get better test data.

The most obvious thing thats wrong is that you have dot-pitch set
wrong "somewhere".

I have *NO IDEA* where dot pitch is configured on XP,
or even if it *is* configured.

   BugBear

Re: Why doesn't 100% zoom in Adobe Reader draw things at the correct size?

Author: Chris Shearer Cooper
Date: Thu, 30 Sep 2010 16:17

48 lines
3129 bytes

On Sep 30, 9:59 am, bugbear <bugbear@trim_papermule.co.uk_trim> wrote:
> Chris Shearer Cooper wrote:
> > I have a very simple PDF file that changes the effective resolution
> > from 72 dpi to 96 dpi (and the origin from bottom-left to top-left)
> > and then draws a line 96 units long:
>
> >         q 0.750000 0 0 0.750000 0.000000 1456.500000 cm
>
> >         q 1.000000 -0.000000 -0.000000 1.000000 48.000000 -48.000000
> > cm
> >         0.0 0.0 1.0 RG 1 w 1 J 100 -125 m 196 -125 l S Q
>
> >         Q
>
> > The line is 96 units long, apply the transformation and it should be
> > 72 units long in the default coordinate system, which would be exactly
> > 1 inch.
>
> > But when I view this PDF in Adobe Reader 8 on my screen (Windows XP)
> > at 100% zoom, the resulting line is almost 1.25" long.
>
> > Wassup?
>
> Use a longer line. to get better test data.
>
> The most obvious thing thats wrong is that you have dot-pitch set
> wrong "somewhere".
>
> I have *NO IDEA* where dot pitch is configured on XP,
> or even if it *is* configured.
>
>    BugBear

New PDF code:

        q 0.750000 0 0 0.750000 0.000000 1456.500000 cm
        q 1.000000 -0.000000 -0.000000 1.000000 48.000000 -48.000000
cm
        0.0 0.0 1.0 RG 1 w 1 J 100 -125 m 580 -125 l S Q
        Q

That line is 480 units long, times 0.75 is 360 units at 72 dpi = 5.00"

On-screen at 100% it's showing up as almost 6 1/8" long, at 72 dpi
that's about 441 units long.

Chris

Re: Why doesn't 100% zoom in Adobe Reader draw things at the correct size?

Author: Matti Vuori
Date: Thu, 30 Sep 2010 16:46

17 lines
2153 bytes

bugbear <bugbear@trim_papermule.co.uk_trim> wrote in 
news:aNedncBGDrVDLjnRnZ2dnUVZ8gCdnZ2d@brightview.co.uk:
> 
> I have *NO IDEA* where dot pitch is configured on XP,
> or even if it *is* configured.

As far as I know, it isn't... XP believes it is 96.

But Adobe Reader itself has a DPI setting... and there is no reason to 
think that it is set correctly. Mine has two options: either a) system 
default - 96 or b) a "modified resolution", which in my case is chosen and 
set to 110 -- and I have no idea where that comes from; I have never set it 
myself.

Anyway, Windows - or any Windows application - has no knowledge of the real 
size of the screen so any DPI value is just guesswork and usually used just 
to scale text and not to configure the technical system.

Re: Why doesn't 100% zoom in Adobe Reader draw things at the correct size?

Author: bugbear
Date: Fri, 01 Oct 2010 08:51

13 lines
2299 bytes

Matti Vuori wrote:
> bugbear <bugbear@trim_papermule.co.uk_trim> wrote in 
> news:aNedncBGDrVDLjnRnZ2dnUVZ8gCdnZ2d@brightview.co.uk:
>> I have *NO IDEA* where dot pitch is configured on XP,
>> or even if it *is* configured.
> 
> As far as I know, it isn't... XP believes it is 96.
> 
> But Adobe Reader itself has a DPI setting

Where? (no really, I don't know)

    BugBear

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