PPI Question...

kidchill · Mar 12, 2008

Okay, I was shooting RAW/Fine with my D80. I went out shooting with the new D300. I have it set for "loss-less compression RAW 14-Bit." I take that and edit the RAW with an output to 16Bit TIFF (I know it's not true 16bit, but I don't wanna downsize to 8bit until I'm done editing). But, when I pull up the file it's only in 240ppi. This isn't making sense to me. The D80 was outputing 300dpi, so why is the D300 only giving 240ppi? Or am I messing something up?

Big Mike · Mar 12, 2008

PPI is only a value used for how an image is displayed on a monitor. You could change it to 300, to 72, to 25 or to 10,000....it wouldn't make a difference to the actual image (as long as you don't re sample as well).

Usually, you can specify what you want it to be, at the RAW conversion stage...but as I said, you can change it to anything you want.

The important numbers to be aware of...is the size of the image in pixels.

kidchill · Mar 12, 2008

Okay, stupid question. If that's the case then why do we bump it down for web and what level should it be for printing? If it's just an arbitrary assignment of a number, why would it matter for the others? Or is it because we're shifting to jpg for web? What happens for printing? Sorry to slam you with questions, but I was hoping you would see this post....

Big Mike · Mar 12, 2008

A monitor only displays something like 72 or 75 PPI...so any higher than that and it's just a waste for web viewing.

When printing, I do change it to 300 PPI (and re-sample it, to make sure that I have 300 pixels per inch of print size).
This way, I can set it to print at actual size.

I believe that as long as you have a sufficient number of pixels in the image...you don't necessarily have to set the PPI because the printer's drivers can take care of that for you.

Maybe it's just too early in the morning...but I feel like I don't have a good handle on how it all works.

As a test, open an image in Photoshop and open the 'Image size' box. Unchecked the 're-sample' box and then change the PPI. You can change it to anything you want...and all that will change, will be the zoom/magnification level of the image.

Now if you do re-sample the image, that's a different story and you will change the number of actual pixels in the image.

kidchill · Mar 13, 2008

OK. I think I kinda, sorta got it. If I ever have prints done I'll be sending it in to a company 'cause my printer sucks for photos. It just seemed kinda odd that the D300 was outputing less PPI...

djrichie28 · Mar 13, 2008

Even at 240ppi it should still be generating 12.2MP images. Your image dimensions should be larger than if it were to deliver an image at 300ppi. If you use Photoshop and change your PPI to 300, you should see the image dimensions shrink but the pixels should stay the same, but only if you uncheck the re sample box.

In the image size adjust in PS uncheck the re sample box witch will disable the option to change the physical pixels. Start to change the value in the ppi box and you will see the dimensions start to change. You can then set the ppi to 300 and you will see the image width and height shrink in size. Since all it is doing is taking the 12.2MP and all the pixels closer together to get 300 of them to an inch instead of 240, but will bring the dimensions in.

If you leave the re sample box checked, it will keep the dimensions and change the number of pixels, which you won't want if you are upscaling.