# 72 dpi ?!



## Rose (Dec 14, 2005)

Hello!

I was just recently told that you cannot (due to poor quality) print an A4 sized photograph a 72 dpi, however i looked at all my files that i have been printing at A4 - with a quality i and my professors at uni thought was more than acceptable- and realised they had a resolution at 72 dpi! I know this has probably been discussed on here before but i was wondering whether i have misunderstood something.  Would people recommend to put the value of 300 dpi into the Resolution dialoge in photoshop (without checking the 'resample image' box) ?

for example images that 'come straight out' of my sony digital camera have this inforamtion:

pixel dimention 14.4 M
Width 2592 pixel
height 1944 pixel

Document size
width 91.44
height 6858 cm

Resolution 72 pixel/inch

Have printed this at A4 and had no trouble so now im confused.. could this be because im printer (canon pixma 4200) simply prints more dpi without me knowing? 

some more knowlege would be appreciated! thank you  










:lmao:


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## Rob (Dec 14, 2005)

Basically this is something which is a bit confusing in Photoshop. You picture looks like it's just about big enough to make an A4 print at 220dpi. Photoshop usually shows the picture at a HUGE size in cm, but at 72dpi. If you were to change the dpi to 300 without checking the resample, then you'll see the maximum size of the image in cm would decrease.

Assuming your document there is 91cm x 68cm (rather than 6858cm!) at 72dpi, then at 300dpi it would be 22cm x 16cm ish which is quite big but not quite A4 size (30cm x 21cm). So it seems likely that your document came out at about 218dpi, which would probably look fine. All numbers are ishy.

Rob


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## Rose (Dec 14, 2005)

so just to clarify, if i set my resolution to 218 dpi (without checking the resample image box) and then print at A4, would i actually see a difference between that print and the one i printed at 72 dpi.?

Only recently did i print an image at 72 dpi which i thought looked pretty bad at A4, but again im not sure whether it was the dpi, or whether it was digital niose (as it was shot with an ISO seeing of 800).

in my cameras instruction booklet is says that if i set my camera to its maximum megapixel setting (4 Megapixel - which i always do) it will print an image at A3! so why do i still get a setting of 72 dpi when i import into photoshop? is there anyway i can change the ppi setting of my camera (have looked and sked many people but they have all said its not possible! )

Is there a way to set the dpi setting for output before i print in the printers settings? However if the image only has a dpi setting of 72, there is probably no point doing that, right?

So as i understand it, my only chance to print at A4 is to change in 'image size' the dpi to 218, but what happens if i want to print at A3 ?? is my camera just not good enough or whats really going on here..?!


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## cecilc (Dec 14, 2005)

Rose said:
			
		

> ...so why do i still get a setting of 72 dpi when i import into photoshop? is there anyway i can change the ppi setting of my camera ...



Don't get hung up on the displayed ppi number of 72 when you open up your image in PS - it's just a number and it's easily changed. It's *NOT* a big deal ..... and there is no way to change that in your camera ..... if it was going to be changed, it would have to be in PS's Preferences section .... you might take a look there and see if there's an option for changing the displayed dpi (or ppi) settings.

What's more important for printing is the pixel depth of your image. And that's just a math problem more than anything else ....

Here's what I mean:

Let's say you open up an image in PS that displays at 72 ppi and the displayed size (at 72 ppi) is 1800 x 2520 pixels. Now, if you print that image at 72 ppi, then you can print an image that's 25" by 35" (1800/72 and 2520/72). But we don't print good stuff at 72 ppi, we print good stuff at 300 ppi. So, if you print that same image at 300 ppi, then you can print a good quality print at 6" x 8.4" (1800/300 and 2520/300).

You can find out what size (at 300 ppi) your image will print at by opening up the "Image Size" option in PS and changing the ppi setting to 300 and *NOT* check the "Resample Image" box at the bottom. To reverse that, to find out what ppi the image will print at for a certain size, in the "Image Size" option just enter your desired size and the ppi number will change to reflect how many pixels per inch will be at that size. Again, leave the "Resample Image" box unchecked.

The "art" has already been taken care of with the photography.

Printing is just math .... multiplication and division .....


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## Big Mike (Dec 14, 2005)

I think you are confusing PPI (pixels per inch) and DPI (dots per inch).  PPI is the resolution of the image file.  DPI is a setting with the printer.

from Bob Atkins



> Display, Printing, DPI and PPI
> There's lots of confusion here so I'll try to go slowly!
> 
> When you display a digital image on a monitor, the only thing that determines the size of the image is the pixel count and aspect ratio. DPI and PPI (and I'll explain them later) mean absolutely nothing. If your image is a 480Kbyte file which is 800 pixels wide by 600 pixels wide, it will display as a full screen image if you are using an 800x600 display. It doesn't matter if your DPI is set to 1 or 1000 or if your PPI is set to 1 or 1000. This is 100% true as far as web display goes and as far as any monitor display goes - unless some software intervenes. For example the IE6 browser will take large images and resize them so they fit on the screen. However DPI and PPI are still ignored. A few advanced page layout programs and advanced image editors may be capable of taking DPI and PPI into account when displaying images.
> ...


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