how do i find out the dpi of a an image on my i mac

Paul, you might take a look at Graphic Converter, I thnk it'll do what you want.

http://www.lemkesoft.com/content/188/graphicconverter.html

Paul Bell1 wrote:

Can anyone please tell me how I find out the dpi of an image on my intel iMac?

I dont have Photshop. I just need to lnow what the dpi is and if its not the right size then maybe make it bigger (if thats possible)

Thanks,

P

With respect to digital images dpi is a meaningless value that can be anything you want it to be. Changing dpi has absolutely no effect on the image, none at all. The only place it ever comes into play is when printing which, from your comment 'if its not the right size...', I believe is your intended use. In printing dpi can be used to 'scale' the image directly. In older print engines this can be an assest. In modern printing systems it isn't really necessary to use dpi to scale images on the printed page but it may still be a convenient way to do so.

Any program that can display image metadata will likely have the capability of displaying and in some cases changing the x and y resolution of the image--also called dpi.

I use ExifChanger for editing EXIF metadata, and ExifExtreme or iExifer when I just wish handle image metadata without bringing up Photoshop CS6, Aperture, Lightroom, or iPhoto. ExifChanger, ExifExtreme, and iExifer are all available in the Mac app store for less than $10 each.

I'm sure there are other apps or methods available--as shown by a simple Google search for 'Mac image metadata'.

Preview should give you the info - with the image selected in Preview do Command+I and it gives you the image data.

Edit: If it's for print reproduction they'll likely need the image in CMYK format rather than RGB.

Paul Bell1 wrote:

Thanks crh24.

You're right it is for printing. It's only a a couple of posters from a pic. The printers say they need 300DPI. I think I've managed to do something in Preview so will see if thats good enough for them.

If not will get that App.

Thanks again.

P

I just checked...the DPI fields can not be modified by ExifChanger...don't know why.

In your case I would just download and install exiftool--a free tool for several platforms written by Phil Harvey. You can then change the dpi with a simple commandline from a Terminal window. For example, if your image file is exift.jpg and it already has the fields for x and y resolution (if not then it takes a separate command to first create them) the Terminal command line would be:

$ exiftool -Xresolution=300 -Yresolution=300 exift.jpg

Good question - without additional software I don't know that you can, although I'm happy to be corrected. I've not used Graphic Converter so I don't its scope/features. In the past I would have used Photoshop (full version). Maybe the printer will do the conversion for you - or perhaps you know someone with the full fat PShop that'll do it for you. It only takes a few moments.

I believe it can be done in Pixelmator as well.

Maybe one of the applications listed here will suit your needs

http://www.marcofolio.net/features/top_15_free_mac_apps_for_graphic_designers.ht ml

Paul Bell1 wrote:

No problem crh24. Thanks for your help anyway.

P

I just edited my last post to include information on exiftool a free program that will do exactly what you wish. You might wish to re-read it.

I've duplicated it here:

In your case I would just download and install exiftool--a free tool for several platforms written by Phil Harvey. You can then change the dpi with a simple commandline from a Terminal window. For example, if your image file is exift.jpg and it already has the fields for x and y resolution (if not then it could take a separate command to first create them) the Terminal command line would be:

$ exiftool -Xresolution=300 -Yresolution=300 exift.jpg

If you just execute:

$ exiftool exift.jpg

Then lots of basic EXIF info, including resolution, is displayed. You might need to put the path info with the file. I didn't need to because I changed my working directory to that of the file.

If you are looking for a free alternative to Photoshop look at

Gimp

http://gimp.lisanet.de/Website/Download.html

You can't just resize an image using Preview.

Resizing an image will change its dimensions, but not the DPI/resolution.

Images on the Internet are usually at computer screen resolution of 72 DPI. Some images in the web might be at 150 DPI depending on the type of website it is.

Just resizing an image will make the image worst as you are only making the available pixels in the image larger and more spread out causing an even blurrier image.

You need an image editor that will increase the number of pixels in an image as you increase the size.

This is called interpolation. You are adding artificial pixels to an image to boost its DPI resolution.

These pixels are created from the surrounding existing pixels in an image.

Done correctly, you can get a pretty sharp image from a low DPI image.

Done incorrectly, you can make the image very ugly, blurry and look very out of focus.

You minimize this effect by increasing the DPI of an image in small increments. I use 50 DPI increments.

Some users use even smaller DPI increments like 25 DPI or smaller.

I have a certain amount of impatience, so I use a larger upscale amount. I still get pretty good results that are more than just acceptable. Some user are just more particular about how much detail and sharpness they want their final image to be. I feel increasing the resolution of an image to 300-350 DPI using 50 DPI increments is a good compromise. My own user preference.

You can't just change a low res 72 DPI image by just changing the DPI to 300 DPI.

All you are doing is spreading out and enlarging the available pixels.

This will make the image worse than it already is.

You need to add additonal pixels to a image by using resampling/interpolation.

And to have this be successful, you need to resample the image in small DPI increments until you reach the desired print resolution of 225, 300 or 350 DPI.

MichelPM wrote:

You can't just change a low res 72 DPI image by just changing the DPI to 300 DPI.

<...>

I'm assuming you intended to say "change a low res 72 DPI image to a higher res image...". Nobody said that. The OP just want's to know how to make it so that his print company will accept the image file. It would be a pretty primitive print company if they mandated that the dpi have a meaningful value in relation to print size the OP desires, but there are a few that work that way. The fact that he mentioned CMYK increases that likelyhood a bit.

How to modify an image to make a large scale print from a low res image file is another subject but you've done a good introduction to the technique in a previous post.

Print scaling isn't hard or complicated, just basic math intensive.