Explain this to me about cropping and dpi...

eric-holmes · Jun 17, 2010

My photo lab has this printed on their website. I don't understand the reasoning for leaving the dpi blank. I just always put in 300.

Oh Crop... So your camera files are a 4x6 format (or you could say 6x9 or 8x12) and you need an 8x10? Well, you either squish that file by changing the dimensions of it to 8x10, and yes this will make your picture look really distorted and funny looking, or you decide what part of the file you are willing to part with and set the crop because obviously, somethings gotta give. If you crop in Photoshop instead of the ordering software, always, always, always, leave the resolution blank. Dont put 250, or 300, or 600. That will just make the file bigger (not better) and will compromise quality and waste your time. Not cropping at all means that you are confident that our automatic "center" cropping will work for the print size(s) you want.

Big Mike · Jun 17, 2010

They are talking about the PPI, not DPI....and the PPI doesn't matter. As long as the file has a sufficient number of pixels, the print should be OK.

Garbz · Jun 18, 2010

The above is half good advice. But the radius of the halo depends entirely on the image size being printed and the resolution of the original. If you create a 1px halo on a 16mpx image that is printed at 6x4 it wouldn't be visible at all. That said if you create a 1px halo on a 5mpx image printed 30x20 then it would look ugly as sin.

This is why it's important to get proofs at the original crop size.

Anyway back to the OP. When you print something the PPI (not DPI as incorrectly used by a lot of people) along with the resolution determines the print size. This is how some printing companies do things. Others will take the opposite approach. They will take any resolution and you tell them what size you wanted it printed and they'll work out the PPI for you.

Garbz · Jun 19, 2010

I know how it works, I was just saying it needs to be tailored to suit the image. I'm not sure about others here but I find I rarely dictate my print sizes by DPI, rather I dictate the PPI by print size.

You take two images with different resolutions (result of cropping or whatever) unless you resize them to a common standard PPI value every time you need to go in and adjust the sharpening method. I think most people here will let the resultion define their PPI value and i.e. print a 6x4 uncropped at 648PPI and a cropped image at 6x4 at maybe 320PPI or something non-uniform. I don't know anyone who goes and resizes all their images for a constant PPI value when they print, actually from what I've seen of discussions there's a consensus that resizing shouldn't be done unless you need to upscale to meet a minimum PPI value.

Not saying your sharpening is a bad thing or not needed, quite the opposite, I fully agree it's a great idea. Just that you shouldn't always zoom in and make the halo 1-2px since a pixel on the image changes on the print based on your PPI.

Dwig · Jun 19, 2010

Garbz said:
...Just that you shouldn't always zoom in and make the halo 1-2px since a pixel on the image changes on the print based on your PPI.

It doesn't when you use the work flow Graystar describes.

With that workflow you create a resampled image sized to the exact print size you are going to print at the optimal PPI for your printer (600ppi in his example). You then, and only then, do the final sharpening. When working that way the 1-2px sharpening halo he describes is appropriate for that print.

This work flow requires that you save a master copy of the image before the resampling and final sharpening. This master image would then be used to create a different resized & resampled image anytime you wanted to make a different sized print or use a different printing device since the final sharpening requires that the image be resampled specifically for the desired print size and printing device before the final sharpening is done.

Garbz · Jun 19, 2010

Yeah I get that. I was pointing out that the sharpening is important, and can be done to fit in with anyone's workflows too. Not everyone goes out and resizes all their images to exactly 600PPI.

I'm discussing options here and not saying any one way is better than any other.

By the way the word you're looking for is "acutance" The measure of a distinctiveness of a line. Haloing created due to sharpening improves this acutance.

I agree that Nik Sharpener is a good tool for that job. I use it myself.

GeneralBenson · Jun 19, 2010

Lots of good info here for someone who is about to print a bunch of stuff for an art gallery... Keep arguing!

Hardrock · Jun 23, 2010

So is something that you do if you only print your own images? I ask because 99.9% of my printed photos come from Mpix. I do not have my own photo printer. So should I be looking into doing this before sending to Mipix?

Garbz · Jun 24, 2010

I just too would like to add that the effect not only depends on the printer, but also on the person doing the printing.

I had a situation like that one day when I got a proof back, gave it the OK and then received an image which looked nasty. They bumped the sharpness and contrast. When I took it back and showed them how it didn't look at all like the proof they explained the just had a new person start and he was different from the person who sent the proof (their excuse anyway, but just watch out for people fiddling with your stuff).