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I am a very new user to POVRAY.
I have rendered and saved my image as an uncompressed Targa file. The image
looks great, but it is only 72 ppi. Is there a way to set the ppi during
rendering in POVRAY? How do people generete publication quality images with
POVRAY???
Thanks,
MARKk
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Markk wrote:
> I am a very new user to POVRAY.
>
> I have rendered and saved my image as an uncompressed Targa file. The image
> looks great, but it is only 72 ppi.
The TGA image file format does not contain any resolution information.
Whatever tells you those '72 ppi' has a different source for this value
than the image.
Christoph
--
POV-Ray tutorials, include files, Landscape of the week:
http://www.tu-bs.de/~y0013390/ (Last updated 24 Jul. 2005)
MegaPOV with mechanics simulation: http://megapov.inetart.net/
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Christoph Hormann <chr### [at] gmx de> wrote:
> Markk wrote:
> > I am a very new user to POVRAY.
> >
> > I have rendered and saved my image as an uncompressed Targa file. The image
> > looks great, but it is only 72 ppi.
>
> The TGA image file format does not contain any resolution information.
> Whatever tells you those '72 ppi' has a different source for this value
> than the image.
>
> Christoph
>
> --
> POV-Ray tutorials, include files, Landscape of the week:
> http://www.tu-bs.de/~y0013390/ (Last updated 24 Jul. 2005)
> MegaPOV with mechanics simulation: http://megapov.inetart.net/
OK, let me ask the question this way...if I open the .tga file in photoshop,
and I want to save the file as a 300ppi eps or .psd file, how would one do
this? I know this is not exactly a POV question, but any help would be
appreciated. When I do this...the resulting images are 72ppi.
Tx.
MarkK
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Markk wrote:
>
> OK, let me ask the question this way...if I open the .tga file in photoshop,
> and I want to save the file as a 300ppi eps or .psd file, how would one do
> this? I know this is not exactly a POV question, but any help would be
> appreciated. When I do this...the resulting images are 72ppi.
In GIMP you can just use Image->Scale and specify whatever you need.
Christoph
--
POV-Ray tutorials, include files, Landscape of the week:
http://www.tu-bs.de/~y0013390/ (Last updated 24 Jul. 2005)
MegaPOV with mechanics simulation: http://megapov.inetart.net/
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Markk wrote:
> I am a very new user to POVRAY.
>
> I have rendered and saved my image as an uncompressed Targa file. The image
> looks great, but it is only 72 ppi. Is there a way to set the ppi during
> rendering in POVRAY? How do people generete publication quality images with
> POVRAY???
>
Don't you want to render your image at a higher resolution? An
Photoshop will allow you to change the ppi under
Image->ImageSize | Resolution
but all that it is doing is resizing the image to a larger resolution,
using, I guess, some mode of interpolation. But it really is not
increasing the amount of information beyond what was in the original
image. I suspect the new resolution it chooses relates to the 133 lines
per inch standard of commercial printing?
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Jim Charter wrote:
> Don't you want to render your image at a higher resolution? An
> Photoshop will allow you to change the ppi under
> Image->ImageSize | Resolution
> but all that it is doing is resizing the image to a larger resolution,
> using, I guess, some mode of interpolation. But it really is not
> increasing the amount of information beyond what was in the original
> image. I suspect the new resolution it chooses relates to the 133 lines
> per inch standard of commercial printing?
Sorry to say, but your guessing is not only wrong but also superfluous:
Photoshop has two modes of operation for changing the resolution. This is
easily controlled in the dialog you mentioned with the "Resample Image"
option. Disable it, and Photoshop just changes the resolution, which
effectively changes the image size in real-world units (i.e. centimeters,
inch, etc) without changing any pixel data. On the other hand, if you
enable "Resample Image", Photoshop will interpolate (using the specified
method in the popup menu next to the resampling checkbox) the pixel data
maintaining the same image size in real-world units.
About pixels:
A pixel is nothing more than an atomic unit of color information. It has no
resolution whatsoever, it does not have a unit it is measured in.
The resolution is implicitly defined by taking a (usually rectangular) block
of many pixels, commonly called an image, which is a specified number of
pixels wide and high. You then can define that the width of the image, lets
say it is 1000 pixels, shall be interpreted as being 2 real-world units in
width.
A real world unit could for example be an inch. In this case, there would
be 1000 pixels to be fitted such that they are two inches in total. Thus,
each pixel is interpreted to be 2 inch divided by 1000 pixel, which equals
500 pixels per inch. You can just as well replace the two by 200, and then
you get 5 pixels per inch. Or you use some other unit to map the pixel
to. The essence is, a pixel has no dimensions, and thus no unit can measure
its size.
In summary: A pixel is just a color information you can interpret to have
any width and any height you like. And that is what is referred to as
resolution.
Thorsten
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> In summary: A pixel is just a color information you can interpret to have
> any width and any height you like. And that is what is referred to as
> resolution.
Good explanation; sadly it seems to be necessary to explain this a little
too frequently.
I've heard of print shops recieving images (must have been in PSD format or
something else that records dpi) and refusing to accept them, saying, "this
image is only 72 dpi, we can't print this." Change the dpi recorded in the
image file to 300 (without actually changing the image data), and they
accept it.
- Slime
[ http://www.slimeland.com/ ]
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Markk wrote:
> I am a very new user to POVRAY.
>
> I have rendered and saved my image as an uncompressed Targa file. The image
> looks great, but it is only 72 ppi. Is there a way to set the ppi during
> rendering in POVRAY?
Okay, this has already been answered quite thoroughly, particularly in
Thorsten's reply, but I'm going to add my own two cents anyway, and
maybe give it a little different slant.
Essentially, the ppi value (or more commonly called dpi--same thing...)
is fairly irrelevant. It is nothing more than a data value in the file
header and is completely independent from the actual image data itself.
(That is, in the graphic formats that support it, which, according to
Christoph, Targa does not.) And it has been pointed out, this value can
be changed with a graphics editor. But I want to emphasize, this
changes that one data value and does nothing to the actual image.
Now, when an image is displayed on a computer screen, this ppi/dpi value
is totally ignored because the screen has a fixed pixel size. The 72
ppi value is usually used as a "generic" average value for computer
screens. Obviously, in reality it varies, nevertheless this value is
used as an average. And this is why 72 dpi is often used by graphics
software as a default value.
However, things change a bit when we come to print the image. Now the
ppi/dpi value _can_ be used -- it might or it might not, depending on
the printing software and the printer's capabilities. If it _is_ used
the print will be this specified "natural" size. But even here, the
printing software will usually have a "print preview" or other means of
adjusting the size (and position) of the printed image, which also makes
the stored ppi/dpi value unimportant.
Now, to your second question...
> How do people generete publication quality images with
> POVRAY???
That's due to the _size_ of the image (in pixel dimensions). More
pixels--higher quality, fewer pixels--lower quality. It's that simple.
The upshot of all this is -- forget about the ppi value. For most
practical purposes this value is totally irrelevant.
-=- Larry -=-
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Well, I've had a lot of problems with a printing shop, because they had a
plotter, but the girl that knew how to use it wasn't there (she was outside
for holidays).
So Slime's problem is very usual, at least for me. The formats is another
problem too. I don't why, but some shops want a .tiff, others a .PSD...
The last year, I needed the print a poster for a congress and I put as a
background a scene with a sky and clouds and I did all the images using
POV-Ray. I decided to give the poster to the printer service from my
university because our project only paid that service. The problem was that
when I saw the poster was awful, all the colors were changed, there were
extrange shadows... And the person from the service said that was my image,
then I printed the image in a shop and, of course, paying the costs from my
pocket and the poster was OK, like on the PC screen.
Regards,
Oleguer
news:430e9362$1@news.povray.org...
>> In summary: A pixel is just a color information you can interpret to have
>> any width and any height you like. And that is what is referred to as
>> resolution.
>
>
> Good explanation; sadly it seems to be necessary to explain this a little
> too frequently.
>
> I've heard of print shops recieving images (must have been in PSD format
> or
> something else that records dpi) and refusing to accept them, saying,
> "this
> image is only 72 dpi, we can't print this." Change the dpi recorded in the
> image file to 300 (without actually changing the image data), and they
> accept it.
>
> - Slime
> [ http://www.slimeland.com/ ]
>
>
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Markk <Markk> wrote:
> I have rendered and saved my image as an uncompressed Targa file. The image
> looks great, but it is only 72 ppi.
How do you know this? POV-Ray certainly doesn't write any PPI info to
the image file (and does targa even support such info?).
And what is PPI in this context anyways? You have a certain number of
pixels in your image file. There are no inches anywhere in a computer
system. How can you compare pixels with inches when there just aren't
none of the latter anywhere?
--
- Warp
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