Re: Default dpi

It is my understanding that DPI is used to scale the image
for printing.  
Monitor display size is based on the number of pixels in the
image.

My monitor is 1280 x 1024 pixels. My 3 MP digital camera
creates an image  
2048 x 1536 pixels with a default 72 DPI. Viewed through
Irfanview without  
alteration, the screen displays roughly 60 percent of the
image. I have to  
scroll to see the rest.

Resizing only the DPI, which is really setting the print
scale, has no  
effect on the display. Resizing the number of pixels does
change the size  
of the displayed image.

When it comes to printing without alteration, using the
default 72 dpi,  
the dimensions on paper would be 28.4 x 21.3 inches.
Changing the DPI to  
scale the picture, for example, at 300 dpi, the 2048 pixel
width converts  
to 6.8 inches; the 1024 pixel height to 5.1 inches.

What I am not clear about is what PageStream does with an
image that is  
sized (in PaintShop, for instance) to a print size of say 4
by 5 inches at  
300 dpi. Does PGS retain those settings. Suppose the image
is sized to 4  
by 5 inches at 600 dpi. Until I print the PGS document, I
haven't  
specified a dpi, so does PGS have a default dpi that it uses
within the  
file until I print it? My point is that each time an image
is resized  
(pixels removed or added), it becomes somewhat degraded. If
I bring the  
image into PageStream at the dpi that it
"expects," then further resizing  
would occur only if I print at some other resolution.

-- 
Best regards,
____
  /om    jojfrostverizon.net

On Sun, 09 Mar 2008 11:41:19 -0400, Don Cox <doncoxenterprise.net> wrote:

> On 09/03/08, Henry G Belot wrote:

...

>> Usually, a paint program will let you
>> change the dpi.
>
> As will almost every image processing program.
>
>> Not that upping it is likely to improve anything
if
>> the original is 72, I suppose.
>
> It doesn't change the data. It changes the scale at
which it is printed
> or displayed.


 
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Hi Tom,

I think you are confusing issues here. I'll be as clear and
concise as I 
can, and if something needs more details let me know.

A typical paint program simply displays dots from a picture
as dots on 
the display in a 1:1 (or if you zoom in, 2:1, 3:1 etc). Very
simple to 
display and very fast.

PageStream on the other hand scales a picture to the frame
you specify 
(to put it as simply as possible). So if you have a
2"x2" frame, and you 
have inside that box a 2000x2000 pixel image, that the
effective 
resolution of that picture is 1000dpi. If you print that
page out at 
200%, then the 2"x2" frame will print as a
4"x4" frame and the effective 
resolution of the image would be 500dpi. Of course, once the
image is 
actually rastered for the printer the resolution is
"fixed" at the 
resolution that you are printing at.

Really, the only time the DPI of an image matters to
PageStream is when 
importing it. If you don't use drag paste to set the size of
the frame 
to place the image in, the frame for the picture is created
for you 
based on the dpi and number of pixels in the image. So if
you have a 
camera picture that says it is 72x72 dpi and it is 3600x3600
pixels, it 
will import it in a 50"x50" frame. At least until
the next release  
Now, in the next release it will not import it more than 75%
of the 
visible page/window, just to confuse things more 

Deron

> It is my understanding that DPI is used to scale the
image for printing.  
> Monitor display size is based on the number of pixels
in the image.
>
> My monitor is 1280 x 1024 pixels. My 3 MP digital
camera creates an image  
> 2048 x 1536 pixels with a default 72 DPI. Viewed
through Irfanview without  
> alteration, the screen displays roughly 60 percent of
the image. I have to  
> scroll to see the rest.
>
> Resizing only the DPI, which is really setting the
print scale, has no  
> effect on the display. Resizing the number of pixels
does change the size  
> of the displayed image.
>
> When it comes to printing without alteration, using the
default 72 dpi,  
> the dimensions on paper would be 28.4 x 21.3 inches.
Changing the DPI to  
> scale the picture, for example, at 300 dpi, the 2048
pixel width converts  
> to 6.8 inches; the 1024 pixel height to 5.1 inches.
>
> What I am not clear about is what PageStream does with
an image that is  
> sized (in PaintShop, for instance) to a print size of
say 4 by 5 inches at  
> 300 dpi. Does PGS retain those settings. Suppose the
image is sized to 4  
> by 5 inches at 600 dpi. Until I print the PGS document,
I haven't  
> specified a dpi, so does PGS have a default dpi that it
uses within the  
> file until I print it? My point is that each time an
image is resized  
> (pixels removed or added), it becomes somewhat
degraded. If I bring the  
> image into PageStream at the dpi that it
"expects," then further resizing  
> would occur only if I print at some other resolution.
>
>   


-- 
Deron Kazmaier - supportpagestream.org
Grasshopper LLC Publishing - http://www.pagestream.org
PageStream DTP for Amiga, Linux, Macintosh, and Windows



 
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Deron:

> ...I think you are confusing issues here....

And I'm now more confused than ever. Be that as it may...

> ...A typical paint program simply displays dots from a
picture as dots on 
> the display in a 1:1 (or if you zoom in, 2:1, 3:1 etc).
Very simple to 
> display and very fast.
>   

If that's "typical," I've never had or used a
typical paint program. My 
programs present each image on the screen in a window large
enough to 
show the entire picture. In essence, they have already
zoomed in or out 
as the image was loaded and the Title Bar for the image
normally shows 
you that expressed as a percentage of the full size;
"PICT1018  35%" or 
"Foobar100%." If you zoom with the manual tools, the
percentage changes 
accordingly overfilling the screen or shrinking the window
when necessary.

> ...[In] PageStream[,] if you have a 2"x2"
frame, and you 
> have inside that box a 2000x2000 pixel image, that the
effective 
> resolution of that picture is 1000dpi.

In my case, "effective" resolution needs
clarification. I'm sure you're 
not saying that the image within PageStream has been
degraded in the way 
that it would be if I saved it from a paint program at a
lower 
resolution. I've recovered images that were saved in PDFs
created by 
PageStream, and the full size image is there at its
"native" resolution 
even though it was much larger than in the original document
or the 
resulting PDF. From this I infer that PageStream
"scales" the image. It 
does not "convert" it to another size. So, yes,
within the document it 
can never have more detail than 1000 pixels and I believe
that's what 
you mean by "effective" resolution?

> ...If you print that page out at 
> 200%, then the 2"x2" frame will print as a
4"x4" frame and the effective 
> resolution of the image would be 500dpi. Of course,
once the image is 
> actually rastered for the printer the resolution is
"fixed" at the 
> resolution that you are printing at.
>   

So, once it's in a document, the printer can never work with
the 
original resolution of the source picture. Whether we
enlarge or shrink 
the page at print time, the image is scaled? But if we scale
up the 
original document within PageStream by changing page and
point sizes and 
doubling the size of the Object Frame, the printer will have
more 
"effective" resolution to start from. Is that
right?

> ...Now, in the next release it will not import it more
than 75% of the 
> visible page/window, just to confuse things more 
>   

Or it may confuse things less at least for those using Place
in Center. 
Either way, it's like the paint programs that retain the
full image in 
memory at full resolution, but display it more conveniently.
Right?

HB


 
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