DPI

[Jimmy Clay]

Hello, I'm trying to get my head around the DPI (Dots per Inch)
concept. It's easy in theory, but I don't feel easy about it. What
I'm doing is preparing a manuscript that will be printed. It has some
graphics in it that are supposed to be set to 300 DPI. I'm trying to
figure out if they are or not.

So just as an example, I have a graphic that I created and saved from
Powerpoint 2007 to a TIFF format. I opened the TIFF file with the
graphic viewer InfanView and got the following information about the
file:

It is 5" X 5"

Resolution is 96 X 96 DPI (this is how InfanView shows the
information)

Size is 480 X 480 Pixels (this is also how InfanView shows the
information)

So, 96 X 96 = 9216. Does that mean this file has a DPI of 9216?

But 480 X 480 = 230400 pixels would be the total pixels for the
graphic. There are 25 square inches, so 230400 / 25 =9216 PPI.
That's the same result as the 96 X 96 DPI.

I'm I right to think that InfanView is giving the "DPI" term a
different meaning than it has when that term is used for graphics that
are to be printed?

Thanks for the help.

 

[Summer]

Your printer laser or inkjet or postscript equipped will determine the dpi
output 600-2400 dpi these days. All tiifs jpegs etc are scanned in at low
resolutions for better results. dpi (dots per inch) is to the human eye and
it means you cannot without a magnifying glass recognise that the dots per
inch are not actually joined together if the document is printed at 600 dpi
or above (being 1200 and 2400 dpi).

So if you are sending your doc to a Printer they will print it at the
correct resolution - if you want to print the document it is dependent on
the printer's dpi capability. These days most printers in the last few years
are 600 dpi minimum in quality print mode (the usual default mode).

I think you need not be concerned at all just send of your Word document to
the printer company.

Hope this helps.

 

[macropod]

Hi Jimmy,

This is really easy!

All you need to do is divide the image's pixel width by the required DPI and the number you come up with is the maximum size the
image should be when pasted into Word.

Taking your "480 X 480 Pixels" image as an example, if you paste that into Word, it should be made no larger than 1.6*1.6"
(4.064*4.064cm).

If that's not large enough, you should use IrfanView or a good graphics editor to resize the image.

To find out how much you need to resize it to, simply take the required dpi (300) and multiply that by the required print width (eg
for a 5" wide print, the required image width would b 5*300=1500 pixels).

Cheers

 

[Helmut Weber]

Hi Jimmy,

http://www.scantips.com/no72dpi.html

http://www.rideau-info.com/photos/mythdpi.html
Pay special attention to the chapter:
"The horrible DPI mistake".

--
Greetings from Bavaria, Germany

Helmut Weber, MVP WordVBA

Win XP, Office 2003
"red.sys" & Chr$(64) & "t-online.de"

 

[CyberTaz]

.... Especially the "DPI vs PPI" topic!

<mini-rant>
It has always frosted me that software developers & "authorities" who should
know the difference - and in fact probably *do* - use the terms
interchangeably [i.e., incorrectly]. It horribly perpetuates the confusion.
<end mini-rant>

Regards |:>)
Bob Jones
[MVP] Office:Mac

 

[Jimmy Clay]

I appreciate the responses and I believe the fog is starting to lift.I
believe there were several things that confused me. I will relate them
because it might help others and to make sure I really do understand.

1. I was not sure if dpi meant dots per square inch or not. But it's
my understand that is not what it means. What 300 dpi means is that
going up one single column of dots, there are 300 of those dots per
inch. And go across for one single row of dots, 300 dpi means there
300 of those dots on that one row per inch.
So if I have column of 300 dpi and a row of 300 dpi that's 90,000 dots
per square inch, but it's only 300 dpi.

2. Another thing that confused me is the way InfaView changes the size
in inches of the graphics when the dpi setting is changed. For
example, If i have a graphic that has the following statistics:
300 dots by 300 dots (I don't mean dpi, I mean the total size of the
graphic is 300 dots up and 300 dots across.)
3.125 inches by 3.125 inches in size
96 dpi

If I change this to 300 dpi, the size in inches changes to 1 inch by 1
inch (because the graphic started out with only 300 dots by 300 dots
and those are all squashed down to a size of 1 inch by 1 inch).

So once I change the dpi setting to 300, I have to go back to the size
setting and change it back to 3.125 by 3.125. And when I do that, that
changes the size of graphic in total dots (not just dpi, but the total
number of dots) to 937 by 937. (3.125 x 300 = 937.5.)

3. And that brings me to the next thing that confused me. Once I make
these changes, and I view the changed graphic in Irfanview, using the
fit window to image option, the file is always larger than expected,
much bigger than 3.125" X 3.125". But that's because IrfanView ignores
the inch setting. Instead if the graphic has 937 dots going up one row
and 937 dots going across one rows, Irfanview sees those dots as
pixels and makes the graphic on the screen of my computer 937 pixels
high and 937 pixels wide, and completely ignores the size in inch,
which would be the size at which the graphic would print. So the size
of the graphic on the screen of your computer, does not indicate the
size of the graphic when printed.

I have a few more questions but I'm going to put them in their own
post.