[Smush]

Hey,

I'm trying to make an Automator workflow to change a batch of images to 300 DPI

Is this possible?

Thanks

[Old Toad]

300 dpi at what size? It's all a number game. A 1600 x 1200 pixel x 300 dpi file is the same as a 1600 x 1200 x 72 dpi file except for the print size. Still the same number of pixels overall in the image.

How are you going to use the file and what print size do you want to end up with? In Photoshop or Photoshop Elements when you change the dpi of a file in the Size pane the print size automatically changes to fit. But the total pixels does not change.

[Smush]

Hmm, it will be used to convert lots of different images for print.

The images are currently 72dpi

Thanks for the reply.

[Old Toad]

All you really need to do is make sure the size ratio of the files is correct for the size of the print. The printing applications will then apply all of those pixels into the print size. A 2272 x 1515 pixel file will print a 4x6 at about 378 dpi. So if the files are cropped to the right size ratio that's all you need to do. UNLESS you're trying to print at a larger size than the file's pixel dimensions can provide at 300. Then you'd have to extrapolate up to achieve the 300 dpi with an application like Photoshop.

[kkthompson]

But it there a way to do what he's originally asking? Change the DPI of a file without changing the number of pixels?

[Old Toad]

Originally Posted by kkthompson 

But it there a way to do what he's originally asking? Change the DPI of a file without changing the number of pixels?

If you take the pixel dimensions of the ile and divide each by 300 you'll get the largest sized print at 300 dpi that can be printed. If that size is too small then there's essentially nothing you can do to put more pixels in the picture to get 300 dpi at the larger size.

If the size to be printed is less than the exact 300 dpi size the print application will print at a higher dpi than 300.

If you really want to have an exact 300 dip file then first a print size must be decided upon. Crop the photo to that size's ratio, i.e. 1.5 for a 4x6, 1.4 for a 5x7, etc. Then multiply the largest side by 300. For a 5x7 that would b e 2100 pixels. Next reduce the pixel dimension of the image file to 2100 for the largest side of the image. Then you will have a 300 dip image file for a 5x7.

However it's a lot of extra work for no benefit. Just crop for the print size and print.