DPI..

Hi all,

I know this may frustrate people to explain this but I just don't get it. I've done my research before asking here too but I really do need it in plain English!

My boss asked myself and my girlfriend to take some photos at their wedding in the summer, they have only just got round to deciding which ones they would like to 'blow up'.

They went to a printers to have this done but unfortunately the printers turned them away saying that the DPI was too small at 72 and to come back when it is 300..

I've been on to Photoshop and adjusted them however I just don't understand why it needed to be done... Sure more dots per inch will make a picture clearer when made larger but where did it get the extra ones from?!

Also, on Photoshop, when changing the image size I selected 'best quality' and that selected 266. Should I select this on all photos they want larger or make them all 300 across the board?

I'm not sure why they couldn't do it themselves but that doesn't matter.

Also, at what DPI do you pros present your clients with to enable them to do whatever they like with the photos?

Thanks in advance

After you downloaded them from your camera, were they saved at 72 DPI? Do you still have the original files (before you converted and saved at 72)?

I'm not a pro, but after I download and do initial processing, I convert and save to the size I want to print, at 300 PPI, (8X10 at 300 ppi, for example), do my final sharpening, and send them off to be printed.

If you're taking an image that's saved at 72, and try to resave at 300, I'm not sure it's going to look very good blown up.

I just download the files to my PC, open them in PS for editing, they are then saved to a separate folder.

Can the edited files not be adjusted to 300DPI now? Am I going to have to open the original files and re-edit them all?

Stuuk1 wrote in post #15571666
I just download the files to my PC, open them in PS for editing, they are then saved to a separate folder.

Can the edited files not be adjusted to 300DPI now? Am I going to have to open the original files and re-edit them all?

If you only saved the processed images at 72, I think you might want to. When your software changes an image from 72 pixels per inch, to 300, it's just making up the extra pixels according to the surroundings. At least that's my understanding. I don't think it will look very sharp.

Just curious. Do you shoot RAW? If I have an image that takes a lot of processing, I convert and save it as a full sized TIFF (after processing). Then it can be sized down/cropped to whatever you want to print.

Well first off pleast take some time and read this "Printing and Enlargement FAQ":

https://photography-on-the.net …/showthread.php​?p=3740438

And then, for a "specific" thread covering "DPI":

https://photography-on-the.net/forum/showthre​ad.php?t=83445

In a nutshell, the print people were likely "old school", dating back to the days before modern digital imaging/printing. Or, they were possible printing with non-digital processing for a print, where having a correct "tag" in the file Exif (300dpi/ppi) matters.

But for "normal" day-to-day printing, that Exif tag really doesn't matter, or at least it shouldn't. In fact, since our Canon cameras "write in" that 72dpi/ppi "tag" automatically, imagine going into that shop with a card of out-of-camera jpegs to have them printed? Would they turn you away? If they have modern digital printers, then if they did they are just showing "old school ignorance"!

Well, there is also the matter of whether it would advantage you to resize your image to 300ppi, that's another thing altogether. In the meantime, the only thing that should matter is that you have an image that you want printed at XxY inches.

However, to appease the old-timers, all you need to do is set the ppi "tag" in the Photoshop Image Size dialog. Open the dialog, turn off the Resample option, leave the dimensions set for Pixels (to avoid confusion) then set the ppi/resolution number to 300 ppi. When you save the final jpeg it will have that in the Exif, but it won't have reized/resampled the image (unless you want that for a specific output).

Stuuk1 wrote in post #15571666
I just download the files to my PC, open them in PS for editing, they are then saved to a separate folder.

I just noticed something:

When checking the Exif of a Canon out-of camera jpeg, the "resolution" shows as 72 (ppi). This is the "old standard" for images being viewed on old low-res monitors. Canon needs to "catch up"...

I then checked a Raw file and the "resolution" figure is blank. In other words, that Exif "tag" gets written as part of the Exif "standard" for image files. Not the 72 part, but the "resolution" part.

I told above how you can change the ppi in Photoshop, just do it prior to saving your final output image. You can also do it in Lightroom, DPP, I presume most editing software lets you change the ppi "tag" as part of saving your file for your final output.

And, once you do this to a file, many if not most editing programs make it "sticky" so that you can, say, do a batch with the same ppi setting.

Remember, though, that this is different between resizing/resampling to a set ppi...

My god, I never realised this!

I feel pretty stupid... The files sizes at 72dpi as a jpg is still around 5mb so its a fair size photo.

I'm just wondering how it will look if i change it to 300dpi in PS but don't want them to waste their money so may have to pay myself first.

I'm hoping my girlfriend has the original files although not sure if she shot the day in jpg or RAW..

By itself, the DPI number that's embedded in the metadata of the file isn't a real number. It's not something measurable, it's just computed based on the original image and the desired print size. Unless you are going to print, it's meaningless. How many inches are in a file that's sitting on your hard drive?

The two REAL things that matter are:
1) The size (in inches) of the desired print
2) The pixel dimension of the image file.
The DPI is calculated based on those two; OR, often you use the DPI to calculate the pixel dimension that you need for a particular print size. But it's still an imaginary number.

A file that's 2400x3000px that says "300DPI" in the metadata is exactly the same as a file that's 2400x3000px that says "72DPI." That embedded metadata is absolutely meaningless. If you print that file at 8x10, you printed it at 300DPI. If you print it 16x20, you printed at 150DPI. If you print it 4 feet by 5 feet, you printed it at 25DPI. A print service that demands that the embedded metadata say "300DPI" doesn't know what they're doing, and I would find a new print service.

Having said that:
If you're resizing the file in Photoshop to a desired size IN INCHES, and you're letting Photoshop calculate the new pixel dimension based on 72DPI, then you've got files with the wrong pixel dimension.
If you told Photoshop that you wanted 8x10 at 72DPI, it would make you a file that's 576x720. That PIXEL DIMENSION is too small to get a nice print at 8x10 INCHES, regardless of what you embed in the DPI field. If you change the DPI field to 300, and the pixel dimension is 576x720, you still can't print it at 8x10. If I get one of those "Hello My Name Is" stickers, and write "Hulk Hogan" on it, it won't change me into Hulk Hogan when I stick it to my shirt. (I tried, it doesn't work)

If you sent the print service a file that's 576x720 and asked them to print it at 8x10, then they are correct to reject it, regardless of what's embedded in the DPI field of the metadata of the file.

So:
1) Figure out what size in inches you want to print
2) Figure out what pixel dimension you need for that size print
Calculate number 2 based on the printer's required DPI for the print medium. Generally this will be 300 but might be much less if you have a large or forgiving print medium. You can get away with 150dpi or maybe even 100dpi when printing on canvas. You can get away with 20DPI when printing a billboard.

If you RESIZED the pixel dimension of your original files, using 72DPI to calculate the final pixel dimension, then yes you need to re-work them. However, if your files are still the original pixel dimension as they came out of the camera, and they just say "72DPI" in the DPI field, then you don't need to re-work them, you need to find a new printer.

nathancarter wrote in post #15571746
By itself, the DPI number that's embedded in the metadata of the file isn't a real number. It's not something measurable, it's just computed based on the original image and the desired print size. Unless you are going to print, it's meaningless. How many inches are in a file that's sitting on your hard drive?

The two REAL things that matter are:
1) The size (in inches) of the desired print
2) The pixel dimension of the image file.
The DPI is calculated based on those two; OR, often you use the DPI to calculate the pixel dimension that you need for a particular print size. But it's still an imaginary number.

A file that's 2400x3000px that says "300DPI" in the metadata is exactly the same as a file that's 2400x3000px that says "72DPI." That embedded metadata is absolutely meaningless. If you print that file at 8x10, you printed it at 300DPI. If you print it 16x20, you printed at 150DPI. If you print it 4 feet by 5 feet, you printed it at 25DPI. A print service that demands that the embedded metadata say "300DPI" doesn't know what they're doing, and I would find a new print service.

Having said that:
If you're resizing the file in Photoshop to a desired size IN INCHES, and you're letting Photoshop calculate the new pixel dimension based on 72DPI, then you've got files with the wrong pixel dimension.
If you told Photoshop that you wanted 8x10 at 72DPI, it would make you a file that's 576x720. That PIXEL DIMENSION is too small to get a nice print at 8x10 INCHES, regardless of what you embed in the DPI field. If you change the DPI field to 300, and the pixel dimension is 576x720, you still can't print it at 8x10. If I get one of those "Hello My Name Is" stickers, and write "Hulk Hogan" on it, it won't change me into Hulk Hogan when I stick it to my shirt. (I tried, it doesn't work)

If you sent the print service a file that's 576x720 and asked them to print it at 8x10, then they are correct to reject it, regardless of what's embedded in the DPI field of the metadata of the file.

So:
1) Figure out what size in inches you want to print
2) Figure out what pixel dimension you need for that size print
Calculate number 2 based on the printer's required DPI for the print medium. Generally this will be 300 but might be much less if you have a large or forgiving print medium. You can get away with 150dpi or maybe even 100dpi when printing on canvas. You can get away with 20DPI when printing a billboard.

If you RESIZED the pixel dimension of your original files, using 72DPI to calculate the final pixel dimension, then yes you need to re-work them. However, if your files are still the original pixel dimension as they came out of the camera, and they just say "72DPI" in the DPI field, then you don't need to re-work them, you need to find a new printer.

This is fantastic, thank you..

I just need to find how to resize the original jpg file... Ill have a play in photoshop at some point, luckily its only 10 images!

Big learning curve this one..

Ok,

I just spoke to the boss and he says that he doesn't want the print any bigger that 24 inches in width..

Do I literally need to just open photoshop with the original picture, edit how I like but before I save, go to image size de-select the (I forgot what it's called..) select 300dpi and select the width as 24 inches?

Do I need to select the height or will that work itself out?

I'm struggling...

If you keep "Constrain proportions" checked, then the height will work itself out. If you un-check that box then you'll get an image that is stretched like silly putty - you're making it wider but not taller. Leave that box checked.

24 inches at 300DPI is going to make a relatively large file (7200 pixels on that edge). IMO, you can get by with less than 300DPI if you're printing at 24 inches. But if that's what the printer wants, so the boss doesn't run into any more hassles, then that's what the boss gets.

Thank you so much guys, this has cleared up a hell of a lot.

Ill go back to the drawing board with the original file which I believe with be a jpg, and have a go at saving that at 300dpi ( http://www.theprintspa​ce.co.uk …xt=print-file-preparation ) this is the company he is using I believe...

Ill do as you say and leave the necessary boxes checked and unchecked and see how I get on.

Thanks again and sorry for wasting your time in something I feel I really should have known.

Stuuk1 wrote in post #15572001
Ok,

I just spoke to the boss and he says that he doesn't want the print any bigger that 24 inches in width..

Do I literally need to just open photoshop with the original picture, edit how I like but before I save, go to image size de-select the (I forgot what it's called..) select 300dpi and select the width as 24 inches?

Do I need to select the height or will that work itself out?

I'm struggling...

O.k., the math is really simple. A 24 inch wide print and you want to have 300 pixels per inch. So you need an image that is 24 X 300 pixels wide. 7200 pixels. That is more than a 60D image which is 5186 pixels wide so you are going to have to resample to get it up to 7200. Therefore, be sure the Resample box is checked. 60D images are 2:3 in aspect ratio (if you haven't cropped it), the same shape as a 16 x 24 print. That height will need 4800 pixels.

After resizing the image it may need sharpening.

That is the DIY way of handling it. The simpler alternative is to not resample and not change anything but the DPI tag and let the printer worry about resizing the image while printing it.

If it were me I would run, not walk, away from that printer and find one who knows what he's doing.

What are the dimensions of the images (in pixels)?

In PS, untick the"resample" box, then put in 300ppi (and don't touch the other boxes). That won't alter the image, only the ppi tag.

If you're going for smallest filesize, you could resample the image to a smaller size.
If the image is (a bit) too small for the desired print size, I'd leave the resampling (upsampling) to the lab, because their software will probably do a better job.

Edit; Everything Elie says.

Stuuk1,

You have encountered a printer who is an absolute moron. Sadly, they are abundant in the world of printing.

As Nathan explained, the DPI number is a meaningless piece of metadata that does not make an image printable or not printable. And anyone in the printing business who doesn't understand that shouldn't be in the printing business.

If I encountered a print shop that thought the DPI value was important, I would go to a different print shop.