changing from 72 dpi to 600 dpi
Brian Bethard
Hello:
I have 5 graphics, all of
which have a size of
72 dpi X 72 dpi.
If I now want to change them
all to 600 dpi (for printing),
how can I do this and still
maintain the nice smooth
clean antialiased look?
I've tried going into
->image ->scale image, but
when I try resizing them,
they start to "grow" in
size and they lose their
crisp sharp look.
Are they different ways
to re-set the dpi to 600?
Any help would be ap-
preciated.
Brian
Jim Townsend
>
> 12/13/01
>
> Hello:
>
> I have 5 graphics, all of
> which have a size of
> 72 dpi X 72 dpi.
You're misreading the information.. The display shows PIXELS per inch (ppi), not DOTS per
inch (dpi) The pixel per inch rating is special, for special applications. The fact
that it is there confuses a lot of people.
> If I now want to change them
> all to 600 dpi (for printing),
> how can I do this and still
> maintain the nice smooth
> clean antialiased look?
Your software (the printer driver you have installed) will read the PIXELS in the image
and change them to the DOTS it lays on the paper. This is almost always a function of
the PRINTER DRIVER, not the image.
If you have a picture that is 1200 pixels wide, and you've set your printer to print the
image 4 inches wide, then there will be a relationship between width and pixels. In this
case you've supplied 1200 / 4 = 300 pixels per inch of printed output.
If you've set your printer to print at 600 dpi, your printer will STILL put 600 dots per
inch on the page despite the fact there were only 300 pixels per inch used to supply the
image information. Your printer driver 'smooths' things out through interpolation as it
converts pixels to dots.
Remember.. no pixels appear on the page.. All you see are the dots who's color and
position were determined from the pixels.
> I've tried going into
> ->image ->scale image, but
> when I try resizing them,
> they start to "grow" in
> size and they lose their
> crisp sharp look.
Set your printer to it's maximum resolution. Concentrate on the print size of the image
(ie 4 inches) then print. If you don't have enough pixels to make a good print, then
you're stuck.. You can't get pixels from nowhere by changing the pixels per inch box.
Print smaller..
Leonard Evens
<bri...@ixpres.com> wrote:
I've been having a hard time figuring out what you are talking about
since you are using terms incorrectly, but I think I've figured out what
you have been doing. You have an image with pixel dimensions 72 x 72
pixels. This is an absolute measurement. No per inch is involved. It
is also a pretty small image, so it is unlikely you are going to be able
to print it and get anything sensible from it.
If I'm right, when you went into the scale image window, then the top of
it showed the pixel dimensions as 72 x 72. You then increased that to
600 x 600 and pressed okay. If you do that, the Gimp will resize the
image to that size, but it will have to interpolate an awful lot of
pixels to do that. Also, anything in the original image will be
magnified by a factor of 600/72 = 8.33. If the original image had lines
in it which didn't have any antialiasing built in, you should see obvious
stairstepping in such lines in the enlarged image.
I'm not sure what the best way to approach your problem is, but let me
give you some general information.
What the Gimp works with is an image which has a specified size in
pixels. Depending on what you tell it to do, it will show that with
appropriate magnification (or zoom factor) so it will fit nicely on the
screen, but that doesn't change anything in the image.
When you go to the scale image window, if you change the dimensions of
the image, it will interpolate extra pixels if you increase the
dimensions and it will average existing pixels to decrease the number of
pixels. The first of these certainly should be avoided if at all
possible since it is bound to degrade the image.
The lower part of that window as best I can tell is purely advisory. If
you increase the resolution figures in the lower window, it will give the
corresponding size in inches of a printed image with that resolution.
As best I can tell, that information is not used by the gimp print
plugin, which allows you to set all that information separately.
Finally, there is no need to send 600 ppi to a printer. Each pixel in
the image needs several dots in the printer. Most authorities agree
that it is pointless to print much over 300 ppi for a typical high
quality inkjet printer, which may in fact claim to deliver 1440 or even
2880 dpit. Probably 240 ppi suffices.
So you should let us know what size you want the final printed image to
be, and perhaps we might be able to suggest what you should do. But it
still seems like a hard nut to crack to get anything reasonable out of a
72 x 72 pixels image, unless you would find something like a 1/2 x 1/2
inch printed image acceptable.
--
Leonard Evens l...@math.northwestern.edu 847-491-5537
Dept. of Mathematics, Northwestern Univ., Evanston, IL 60208
Mark T
are making more pixels, but not providing more information to populate them.
A grid of 8x8 black pixels at 600 dpi doesn't print any different from a
single black pixel at 72dpi - and that is what happens when you upsample.
The image won't look very different from the original at the same size,
because there is nothing to fill in the fine detail.
There are some interpolation programs, like Fractal Explorer, which use
mandelbrot geometry to 'guess' what the finer detail should be - It's pretty
impressive with avoiding the jagged edges that you would otherwise have, so
so in other areas.
I know it works with Photoshop and PSP - not so sure about it working with
GIMP.
Mark
"Brian Bethard" <bri...@ixpres.com> wrote in message
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