# iMac 17" Monitor dpi?

Discussion in 'Macintosh Computers' started by Rhobes, Dec 11, 2004.

1. ### Rhobes macrumors 6502

Joined:
Oct 28, 2004
Location:
Missoula,MT
#1
Hello all....

I have an iMac (OS 10.3.6) with the 17" LCD display that I have set on 1440x900 resolution. I'm assuming it dosen't matter what the resolution is set at, the monitor should still display at the same dpi???

What is the monitors dpi?? I don't see it anywhere in my Apple information. My PhotoShop user Guide says "most newer Mac monitors are 96 dpi & the older ones are 72 dpi.

Knowing the monitor dpi will help me in understanding the optimal resolution to use while creating & printing to my 720 dpi Epson.

Thanks for any info on this..........

2. ### Daveman Deluxe macrumors 68000

Joined:
Jun 17, 2003
Location:
Corvallis, Oregon
#2
Measure the vertical length of the display with a ruler. Divide 900 by the number of inches. That's the resolution in DPI.

3. ### Daveman Deluxe macrumors 68000

Joined:
Jun 17, 2003
Location:
Corvallis, Oregon
#3
Heck, I just did it for you using basic algebra.

100 dpi.

4. ### Rhobes thread starter macrumors 6502

Joined:
Oct 28, 2004
Location:
Missoula,MT
#4
O.K that seems to work for the 1440x900 monitor resolution. The screen measures 14.4"x9". 900/9"=100 & 1440/14.4"= 100 dpi. The text books state the newer Macs should be ~100 dpi, so yes this works. But.............

Lets say I set my monitor to 800x600. Following the above method I now find: 600/9"= ~67 & 800/14.4"= 56 dpi. Here is a 10 pixel(dot) difference between the two lengths, so do I now have a 67 dpi or a 56 dpi monitor or the 100dpi from above????

Yet the texts always mention monitor dpi as a fixed element, thats what I don't understand, in the first case you have a very logical 100dpi monitor across the vertical & horizontal axis. In the 2nd case you have unacceptable values for dpi varing by 10 points between the axis (56 & 67 dpi) & these are greater than 30 dpi less than the first case.

So,.... I take it that dpi "IS" dependent on set monitor resolution, & the text editors are always refering to the highest resolution a moitor can make??

In this situation, if I wanted to print a known dpi to a photo printer for optimal results I should do my photoshop work at the 1440x900 monitor resolution which works out to a nice 100 dpi Vertically & horizontally, sound correct??

Thanks Rhobes.....

5. ### Daveman Deluxe macrumors 68000

Joined:
Jun 17, 2003
Location:
Corvallis, Oregon
#5
That's an interesting question, but I know the answer.

A LCD monitor has what's called a "native resolution". That's the actual number of horizontal and vertical pixels the LCD physically has--in this case, 1440 horizontally and 900 vertically. That works out to 100 dpi.

This means that the aspect ratio--the ratio of the horizontal to the vertical resolutions: is 1.6:1.

Taking your example of 800x600, the aspect ratio is 1.33:1. That's where you run into the problem you stated. To place nonnative resolutions on monitors, most computers use interpolation to stretch each individual pixel out so that each logical pixel covers more than one physical pixel. This tends to be blurry since it's rare for each logical pixel to cover an integer number of physical pixels.

In OS X, widescreen resolutions are very commonly encountered. When using a 1.33:1 aspect ratio, you have two options. You can set it for 800x600, where the horizontal and vertical dpi are equal but you have black bars on the right and left side of the screen, or you can use the "800x600 (stretched)" option, where it stretches the 800 width out to fill the entire space of the monitor. That's when you get the problem with "56 and 67 dpi" that you mentioned.

Hope this helps.

6. ### zim macrumors 65816

Joined:
Jan 5, 2002
#6
ppi (pixels per inch) not dpi (dots per inch).

7. ### decksnap macrumors 68040

Joined:
Apr 11, 2003
#7
I don't understand the connection between your monitor's dpi and the dpi of your file in Photoshop as far as printing is concerned. As long as you know the dpi of your file in Photoshop, you'll know what kind of quality print you are going to get. That's between Photoshop and your printer- nothing to do with your monitor.