Hi everyone

I need to create a picture with a specific size and resolution.
I am Linux user so I have a .ini file which contains info like the picture
size in pixels, e.g. :

Width=4000
Height=3200

But, I don't how to set the resolution. I've actually been asked to create a
picture with 300 DPI with a size of 213 x 161 mm

How do I do that ?

Cheers guys

Dav

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Dav_shef wrote:
> I need to create a picture with a specific size and resolution.
> I am Linux user so I have a .ini file which contains info like the picture
> size in pixels, e.g. :
> 
> Width=4000
> Height=3200
> 
> But, I don't how to set the resolution. I've actually been asked to create a
> picture with 300 DPI with a size of 213 x 161 mm
> 
> How do I do that ?

Please read the messages in the thread started with

From: "Markk" <Markk>
Date: Thu, 25 Aug 2005 11:32:03 EDT
Newsgroups: povray.newusers
Message-ID: <web.430de4731026f62e8ebe11d70@news.povray.org>
Subject: Specifying ppi
Xref: news.povray.org povray.newusers:12918


	Thorsten

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In article <web.432ad3458a10e857703346660@news.povray.org>,
 "Dav_shef" <nomail@nomail> wrote:

::Hi everyone
::
::I need to create a picture with a specific size and resolution.
::I am Linux user so I have a .ini file which contains info like the picture
::size in pixels, e.g. :
::
::Width=4000
::Height=3200
::
::But, I don't how to set the resolution. I've actually been asked to create a
::picture with 300 DPI with a size of 213 x 161 mm
::
::How do I do that ?
::
::Cheers guys
::
::Dav

simple : 1 inch = 25.4 mm

213 mm -> 213/25.4 at 300dpi -> 300*213/25.4 = 2515
161 mm -> 161/25.4 at 300dpi -> 300*161/25.4 = 1901


:)
klp

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> I need to create a picture with a specific size and resolution.
> I am Linux user so I have a .ini file which contains info like the picture
> size in pixels, e.g. :
> Width=4000
> Height=3200
> But, I don't how to set the resolution. I've actually been asked to create a
> picture with 300 DPI with a size of 213 x 161 mm
> How do I do that ?

DPI is "irrelevant", what you want to know about from a printing/quality 
point of view is the number of pixels. DPI only comes into the game when
you consider printing an image at a paricular size. For example, your 4000
pixel wide image above, if printed 10 inchs wide will be 400DPI. The exact
same image printed at 20 inchs will be 200DPI.....a clear example of why
DPI as a measure isn't so useful.

The problem is that the printing industry is so steeped in the use of DPI
that they often don't understand what's really going on. So when they give
you a DPI value and an image size you simply multiply them to give the
right number of pixels. So for your example 300DPI at 213mm is
   300 * 213 / 25.4 pixels
or about 2500 pixels. 

Now most image formats do have a DPI setting as part of the file information,
but again it is largely irrelevant except at the point of actually representing
the image on some media. It is the number of pixels that determines the 
(potential) resolution and information content.

-- 
Paul Bourke
pdb(NOSPAM)swin.edu.au

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Dav_shef wrote:
> Hi everyone
> 
> I need to create a picture with a specific size and resolution.
> I am Linux user so I have a .ini file which contains info like the picture
> size in pixels, e.g. :
> 
> Width=4000
> Height=3200
> 
> But, I don't how to set the resolution. I've actually been asked to create a
> picture with 300 DPI with a size of 213 x 161 mm
> 
> How do I do that ?
> 
> Cheers guys
> 
> Dav

You can't set the dpi within POV-Ray itself, but you can do it 
'after-the-fact' with virtually any graphics editing program.  In 
PaintShop Pro, for example, it's a setting in the resize dialog box.
Oops, that's Windows -- I now noticed you said Linux.  In the Gimp, it's 
Image->Print Size.

All this does is change a data value in the header of the image file -- 
it does absolutely nothing to the image itself.

In your requested picture, 213 x 161 mm is 8.39 x 6.34 inches, so at 300 
dpi it's 2516 x 1902 pixels.

      -=- Larry -=-

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Larry Hudson wrote:
> Dav_shef wrote:
...
>> I need to create a picture with a specific size and resolution.
...
>> Dav
> 
> You can't set the dpi within POV-Ray itself, but you can do it 
> 'after-the-fact' with virtually any graphics editing program.
...
>      -=- Larry -=-

I should have also mentioned, as did several others in this thread, that 
the dpi setting is in reality generally irrelevant.  Nevertheless, it 
_is_ possible to adjust it with graphics editing software.  (Sometimes 
it's rather obscure to find, but it's usually in there someplace.)

      -=- Larry -=-

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Paul Bourke wrote:
> The problem is that the printing industry is so steeped in the use of DPI
> that they often don't understand what's really going on. So when they give
> you a DPI value and an image size you simply multiply them to give the
> right number of pixels. So for your example 300DPI at 213mm is
>    300 * 213 / 25.4 pixels
> or about 2500 pixels. 

As a member of the pre-press industry, I'm going to take extreme 
umbridge at that! We do understand exactly what's going on. After all, 
it's our livelyhood.

The problem comes from non-printing people not understanding what we 
mean by DPI (and therefore by default, it is our fault for not 
explaining ourselves fully).

These days the correct term is PPI (pixels per inch). It defines the 
number of pixels of data we get in every inch in some output format.

We ask for an image to be at 'at least 300ppi' meaning that we need the 
image to be at 300 *effective* pixels per inch (eppi). That means that 
the internal file tag may say that the resolution is 300ppi but the data 
is all still pixels.

We LIKE the image to have this internal tag as it makes it easier to 
deal with the image once it comes into our page layout application. If 
you provide an image tagged at 72ppi (or untagged), and we need to lay 
it into the page at an eppi of 300dpi, we need pull out our calculators 
and work out that 72/300 ... = 0.24 .. so we can't place the picture any 
larger than 24%.

Later we come back to the layout to make the picture larger (for some 
design reason) and notice that it's at 24% .. so, forgetting that it's 
untagged, we figure we can make it 4 times as large without any 
problems. But of course, we can't. That's why we want the image at the 
correct ppi from the start.

Cheers!
Rick Measham

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Oh come on! It is just a hang over from the early days
of off-set printing. I remember getting black and white
photos printed through screens to get the resolution (in
dpi) that the off set printer could handle without smudging.
In that context it meant a lot. Today it's just dumb.

It should be irrelevant today. You can digitally resize
images to whatever dpi limits your printer has. As you say
your OUTPUT hardware has limitations defined in dpi, just
as it did 30 years ago. So yes, printers have to deal with
dpi, but there's no reason to ask for digital images defined by
both x-y dimensions and "ppi". To do so is either irrelevant
or redundant. The artist doesn't need to know how many square
inches you plan to cover with the pixels, only the number of
pixels.

If I have a 3000x2000 image it means nothing to give
it an internal tag of 72 dpi. If you resize it that internal
tag still means nothing.

The whole thing is so irritating because you need an
additional, and confusing piece of information. What
really upsets digital artists is that print oriented people
will ask for something by only specifying dpi. Completely
meaningless without the number of x and y inches. Then
you say, "yeah, but how large" and repeat the dpi! Augh!

> it makes it easier to deal with the image once it comes into our page 
> layout application

Only because the software was designed for old school
printers who still think in terms of "dpi". Layout workers and
the software could completely disregard "dpi" until the finished
product is sent to the printer. In the old days it was difficult
or sometimes impossible to change an image to a different
resolution. In the analog days if you took a photo screened to
300 dpi and tried to rescreen it to a different odd dpi you would


I say it is an just an old school tradition that print media people
can't get over. It gives them a little convenience (even that
could be handled automatically by software anyway)
at the cost of confusing everyone else with an irrelevant
specification.

But I could be completely wrong. :)
I don't do much print layout :)

"Rick Measham" <rickm*at%isite.net.au> wrote in message 
news:432cdb5e$1@news.povray.org...
> Paul Bourke wrote:
>> The problem is that the printing industry is so steeped in the use of DPI
>> that they often don't understand what's really going on. So when they 
>> give
>> you a DPI value and an image size you simply multiply them to give the
>> right number of pixels. So for your example 300DPI at 213mm is
>>    300 * 213 / 25.4 pixels
>> or about 2500 pixels.
>
> As a member of the pre-press industry, I'm going to take extreme umbridge 
> at that! We do understand exactly what's going on. After all, it's our 
> livelyhood.
>
> The problem comes from non-printing people not understanding what we mean 
> by DPI (and therefore by default, it is our fault for not explaining 
> ourselves fully).
>
> These days the correct term is PPI (pixels per inch). It defines the 
> number of pixels of data we get in every inch in some output format.
>
> We ask for an image to be at 'at least 300ppi' meaning that we need the 
> image to be at 300 *effective* pixels per inch (eppi). That means that the 
> internal file tag may say that the resolution is 300ppi but the data is 
> all still pixels.
>
> We LIKE the image to have this internal tag as it makes it easier to deal 
> with the image once it comes into our page layout application. If you 
> provide an image tagged at 72ppi (or untagged), and we need to lay it into 
> the page at an eppi of 300dpi, we need pull out our calculators and work 
> out that 72/300 ... = 0.24 .. so we can't place the picture any larger 
> than 24%.
>
> Later we come back to the layout to make the picture larger (for some 
> design reason) and notice that it's at 24% .. so, forgetting that it's 
> untagged, we figure we can make it 4 times as large without any problems. 
> But of course, we can't. That's why we want the image at the correct ppi 
> from the start.
>
> Cheers!
> Rick Measham
>

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