How to change a photo's DPI?

[swcricket98]

Hi everyone! I'm Sylvia. I recently won a photography contest and the administrators have recently requested that I alter the DPI from what is now 480 to 300. How should I go about changing it? Thanks for any help!

[Colin Southern]

Hi Sylvia,

DPI and PPI are one of the most mis-understood things about images. First up, DPI is usually set by the printer and isn't normally changed - so I'm guessing that you're actually talking about PPI (to do with the number of pixels in an image)?

Can you tell us a little more about what it is that you're needing to do - are we talking about a physical print of just an image to be displayed on the internet?

[Macmahon]

Hi everyone! I'm Sylvia. I recently won a photography contest and the administrators have recently requested that I alter the DPI from what is now 480 to 300. How should I go about changing it? Thanks for any help!

Hi Sylvia

I would guess that the reason the admins want to you to change this is that they want to print the image on a printer whose native resolution is some multiple of 300 dots per inch, such as one of the larger format Canon ink jet printers.

However, how you go about it depends what software program you're using to output the image: Photoshop? (Colin's the Photoshop man, he'll be able to help ) Lightroom? Aperture? something esle???

Tim

[Colin Southern]

Hi Sylvia

I would guess that the reason the admins want to you to change this is that they want to print the image on a printer whose native resolution is some multiple of 300 dots per inch,

The problem is Tim, DPI is a function of the printer - not the photo - and it thus out of the photographers control.

[Splatsworth]

I did a beginners photography course a ways back and they touched on printing, photoshop has a setting but for the life of me a can't remember where/how, I think it might have been under image size, the tutor did explain things but me being an er.... "older" student my poor old brain didn't retain it

[Colin Southern]

I did a beginners photography course a ways back and they touched on printing, photoshop has a setting but for the life of me a can't remember where/how, I think it might have been under image size, the tutor did explain things but me being an er.... "older" student my poor old brain didn't retain it

Hi Trev,

You're thinking of PPI, not DPI.

[Splatsworth]

Hi Trev,

You're thinking of PPI, not DPI.

Hi Colin

Ah cheers for the reminder, yet another of my senior moments I can remember we had to submit an image to Proam for printing and as part of that we changed that setting, hopefully thats what Sylvia needs to change.

Trev

[Donald]

Sylvia

It seems like the guys on here are not clear about what it is you are being asked to do. Which makes me think that maybe the Admins weren't clear with you about exactly what they are wanting.

Maybe you can get the admins to send you an e-mail with their precise request, which you can then post up here. That might then allow people a clear answer to the question they are asking.

ps - Welcome to CiC. I hope you'll stick around on the forum and become an active member.

[Fit]

This matches my understanding:

http://www.rideau-info.com/photos/changedpi.html

My HP printer for example has no adjustment for DPI. It only offers whatever the photo's data says.

[Macmahon]

The problem is Tim, DPI is a function of the printer - not the photo - and it thus out of the photographers control.

Yeah. I guessed Sylvia was being asked to adjust ppi to match the dot pitch of the printer. Matching the pixel pitch from the sensor to the dot pitch on a printer is square peg and round hole for the most part. Something gets squeezed from its comfort zone. Nevertheless, most software does it painlessly, if not uniformly well.

Tim

[swcricket98]

Thanks for all of the concern, everyone. This is the exact message:

"Please send us by Monday 5th March 2012 a high res JPEG (300dpi) of this image."

Does this help any? It will be printed and shown at an art gallery.

[rpcrowe]

I have had some of the expected recipients of images ask for 300dpi. I don't think that tey really knew what they wanter OR their printer did not know what to ask for. I provided them with full size images from my 1.6x cameras (I tend to crop minimally) at 240ppi resolution and they appeared satisfied.

[Colin Southern]

It's definitely PPI that they want - not DPI.

Before you can give it to them at 300 PPI you'll need to know what size it's going to be printed. Once you know that someone here could resample it in a few seconds for you.

[Noice]

id wager its the administrators fault. they probably meant PPI as well.
i know i generally use DPI.

at any rate, 480 PPI is excessive.
i would usually set mine to 240-300

[swcricket98]

If I didn't make myself clear, my photo is now 480 DPI. I need it to be 300. I know this because I looked at the photo properties and it said that there. Are you sure she's talking about PPI? How would I go about changing it?

[Colin Southern]

If I didn't make myself clear, my photo is now 480 DPI. I need it to be 300. I know this because I looked at the photo properties and it said that there. Are you sure she's talking about PPI? How would I go about changing it?

DPI (DOTS Per Inch) is the physical number of dots of ink that a printer lays down on the paper as it's printing the image -- it's not a property that can be applied to a photo in electronic form. Many folks say DPI when they're really meaning PPI (PIXELS Per Inch) though (I often make the mistake myself).

Just when you thought it couldn't get any more confusing ...

A given PPI can only be stated if the size of the image is also stated (on the computer) - it's simply the number of pixels contained in each dimension of the image divided by the size of the image (in inches). So if - for example - your image is currently 480 PPI - and you've told your processing program that the image is 6 inches by 4 inches - then that would mean that the image had 2880 x 1920 pixels. One way to "change" the 480PPI to 300PPI would be to simply print the image 9.6 x 6.4 inches in size. If it were desired to keep the image at 6 x 4 in size then one would have to reduce the number of pixels to only 1800 x 1200.

Hope that's not too hard to understand. It does confuse a lot of people (more than it should I feel). The thing is that good folks see existing figures like "480" in a program but don't understand that the figure they're seeing is relative to the size of the image specified; so until we know what size the image is to be printed, it's not possible to know how many pixels are going to be needed to print it at the requested resolution.

To make matters worse - as a general rule (and printing fine art for galleys walls is one of the things I do for a living) - figures like "300" are a minimum quality indicator (albeit an excessively high one in my opinion) - if an image is set to something higher then it doesn't matter (it won't be visible anyway so not needed, but no harm anyway).

In summary, (a) we need to know the printed size, and (b) what they're asking for is wrong (ppi needed not dpi) and unnecessary (assuming the image is already set for the correct size) then 480 is better than 300.

As a case in point, here's 2 versions of the same image - the fist is saved as 10 PPI and would measure 60 x 75 inches if printed - the 2nd is saved at 1000 PPi and would measure 0.6 x 0.75 inch if printed ...

[Macmahon]

If I didn't make myself clear, my photo is now 480 DPI. I need it to be 300. I know this because I looked at the photo properties and it said that there. Are you sure she's talking about PPI? How would I go about changing it?

Sylvia

Firstly, congratulations on having had an image selected for a gallery. Well done!

If you're using a program like Lightroom you choose 'export'; then select JPEG Maximum Quality under 'file format', and 300 ppi under 'image size'. The software will do the rest as it creates the file to send.

If you're using Photoshop, look at http://www.youtube.com/watch?v=7YDsJszDiBI. I'd do this procedure on a copy of your image, because you won't be able to get back to your original after you've completed this. That process is the same as Photoshop Elements.

If you are using some other software, the routine should/might be similar: maybe 'save as' rather than export.

If you can't find a ppi adjustment in the dialog, I'd just go for saving/exporting JPEG Max Quality, and Image size maximum. The administrators' printing software should/will probably resample automatically if it has to.

However, all this said, I wonder what has prompted them to specify 300 ppi since their printing software will almost certainly be able to resample assuming you provide enough data (max size, max quality). As Colin says, someone on this forum could resample in a few seconds but so should the 'administrators' be able to if they know what they are doing and/or why they need 300ppi.


Tim

[Colin Southern]

If you're using a program like Lightroom you choose 'export'; then select JPEG Maximum Quality under 'file format', and 300 ppi under 'image size'. The software will do the rest as it creates the file to send.

The problem is though Tim that we don't know what size the photo is to be printed; if it's currently set to 6 x 4 & is resampled to 300PPI - and they want to print the image as a 12 x 8 - then it'll only be 150PPI. So if the OP can just tell us the printed size then we can fix the problem in a couple of seconds.

[swcricket98]

I have emailed the woman with some of your questions and am hoping for a reply soon. I will keep you posted.

[Macmahon]

The problem is though Tim that we don't know what size the photo is to be printed; if it's currently set to 6 x 4 & is resampled to 300PPI - and they want to print the image as a 12 x 8 - then it'll only be 150PPI. So if the OP can just tell us the printed size then we can fix the problem in a couple of seconds.

Yes. But Sylvia said her current files was 480 ppi, and I guessed, possibly foolishly, that they want the same sized image.
What could be more of a concern is that no colour space is mentioned. If the 'administrators' aren't capable of downsampling it's entirely possible equipment either isn't properly colour managed. Let's hope the image is a black and white!

Tim