72 dpi Hi-res?

bethtphotos · 04-01-2009, 04:17 PM

I recently photographed some products for a catalog and print job with my Pentax K10D. The resulting photos were recorded as 72 dpi, with a size of 3592 x 2572 pixels.

The client has come back to me complaining that these are lo res images, not hi res, as is evidenced by the dpi.

I understood that these were hi res images. Am I wrong? and if so, how can I create hi res images for my client. If I'm right, how can I explain this so my client will understand?

Thanks for your help.

Jim Royal · 04-01-2009, 04:46 PM

The photos are indeed high-resolution. If they were printed at 72 dpi then that would be a low resolution print -- an enormous one, because the printed photo would be 50 inches across.

The DPI refers only to the printed resolution, and that value can be set to any number you like. It has nothing to do with the actual resolution of the photo, and it can be changed without affecting a single pixel in the image.

If you have Photoshop, you can make this change in the Image Size dialogue box. Make sure Resample Image is turned off when you change the DPI value.

flyer · 04-01-2009, 05:14 PM

For printing, they are low-res. Ask your customer the printed size of the pictures, and size them accordingly at 300 DPI. For the printing process, they can use anything from 133 DPI up to 300 DPI on the presses, but to be able to integrate everything in the pre-press dept, they"ll need 300 DPI or more.

**Marc Sabatella** · 04-01-2009, 05:40 PM

Your client has no idea what he is talking about, but unfortunately, his confusion is common, the dpi fgure recorded in the file has absolutely no relevance whatsoever. The 72dpi number means nothing. All that matters is how many pixels there are. If there are 3000 pixels and you print it 10", there are 3000 / 10 = 300 pixels per inch, simple as that.

But if he cannot accept that, simply find a program that lets you change that 72 to whatever number he wants it to be. it won't have the slightest effect on anything, but if it makes him happy, smile and accept his money.

Jim Royal · 04-01-2009, 08:59 PM

Originally Posted by flyer

For printing, they are low-res.

Flyer, those are 10 megapixel images. It is misleading to call them low-resolution just because the dpi value is low. They will print just fine.

bethtphotos · 04-02-2009, 05:36 AM

Thanks for the feedback. I've printed photo cards & photo books with these resolutions in the past, and had beautiful results, so I'm just not sure what the issue is, although perhaps the file was compressed in email transmission (thats certainly possible).

I'm taking Jim's advice: opened the file in Photoshop, changed the dpi to 300 with an unchecked Resample box. Then I've both emailed the file & sent a copy on a DVD, so that I can then take Marc's advice to smile & take the money.

Thanks Again!

emalvick · 04-02-2009, 11:27 AM

This is a little aside/rant, but isn't a camera recording 72 dpi by default a bit of a joke...

72 dpi is supposedly the screen resolution, but when does any software actually use the 72 dpi to actually view an image or for any other purpose?

In other words, why do cameras (or even software if that's the case) record 72 dpi to the images in the first place? It seems it would make more sense if a camera just defaulted to 300 dpi. At 300 dpi, even my original 2 MP camera would have been fine at its 1200 x 1800 resolution for a 300 dpi 4 x 6 (the most common print size people order).

Jim Royal · 04-02-2009, 01:34 PM

Emalvik: If you were to print your 2MP images (which had a setting of 72 dpi) at the size of 4x6, they would look exactly the same as printing a 2MP image with a setting of 300 dpi at a size of 4x6.

The DPI value inside the file is only a suggestion as to how software should handle the file, for example, how the photo would be imported into a desktop publishing application.

DPI is meaningless without also referring to printed dimensions. A 2 MP image printed at a size of 4x6 actually has a printed resolution of 300 dpi. DPI is meaningless until the photo is actually output onto paper. A 2MP image printed at 72 dpi would be 25 inches across.

**Marc Sabatella** · 04-02-2009, 02:21 PM

Originally Posted by bethtphotos

Thanks for the feedback. I've printed photo cards & photo books with these resolutions in the past, and had beautiful results, so I'm just not sure what the issue is, although perhaps the file was compressed in email transmission (thats certainly possible).
]

No, it's just that the camera sticks the number "72" into the EXIF information of the file where it's supposed to pick a resolution. The number is, as I've said, completely meaningless, but there's got to be something there, so the camera picks 72, which happens to be a traditional resolution for viewing on screen. That doesn't mean the picture can only be viewed on screen, though. If you print it, it will come out what whatever resolution you get by dividing the number of pixels by the size of the print.

The best analogy I can imagine is a car came with a picture of its dashboard in the user manual, and in the manual, that picture shwoed it going 72MPH. Thast doesn't mean your car is actually going 72MPH at all times; it's just a picture for demonstration purposes and the speedoment had to be reading *something*! Similarly, the resolution figure stored by the camera in the EXIF is not the *actual* resolution; it's just a number stored there because there is a palce to store a number so it's got to put *something* there.

With the car, your actual speed is determined by how hard you press down on the gas pedal and has *nothing* to do with what the speedometer reads in the picture in the manual. With the camera, the resolution is determined by how big you print the image and has *nothing* to do with what number is recorded in the EXIF.

*khardur* · 04-02-2009, 03:32 PM

my company has a "pre-press" department. They evaluate artwork supplied by our customers and tell them whether it's okay or not. In the past few years we started printing digital photos on cards. They started rejecting photos because they were 72dpi. I had to explain to them that this is standard for a jpg from a digital camera, and what they need to worry about is the pixel dimensions, not the dpi.

It took half an hour to get them to say "oooohhh.."

*graphicgr8s* · 04-02-2009, 09:41 PM

Originally Posted by khardur

my company has a "pre-press" department. They evaluate artwork supplied by our customers and tell them whether it's okay or not. In the past few years we started printing digital photos on cards. They started rejecting photos because they were 72dpi. I had to explain to them that this is standard for a jpg from a digital camera, and what they need to worry about is the pixel dimensions, not the dpi.

It took half an hour to get them to say "oooohhh.."

Time for your prepress people to find another line of work. And no, I am not available.

*khardur* · 04-03-2009, 03:35 AM

Originally Posted by graphicgr8s

Time for your prepress people to find another line of work. And no, I am not available.

hah.

I wasn't quite so harsh on them as you would be. They've been working exclusively with 1-bit line art and fonts for their entire graphic lives, and for those the requirements are much stiffer than with printing photos. So I can understand why they were confused.

Andreas · 04-03-2009, 04:17 AM

I quote from an earlier post of mine (slightly edited) from another thread:

72 DPI is the number of actual physical pixels in an inch on the original Macintosh screen in 1984: that particular screen, combined with a fixed resolution, had 72 screenpixels on 1 inch. Therefore Apple could say that they were truely WYSIWYG: if a font was 14 points on paper (= 14/72 of an inch), it was shown at the same size on that particular screen from 1984.

Since screens now come in varying sizes, can display various resolutions and, on top of that, the visual part of it can be scaled, this number has no meaning nowadays. Except that there is a convention that says: we'll pretend that our screen shows 96 pixels per inch (Windows) or 72 pixels per inch (Apple), although it does not, and if we represent a 14 point font on screen (14 point = 14/72 inch on paper), we will use 14/72 * 96 = 19 pixels for that on screen (Windows) or 14 pixels (Apple) (I'm talking about font height here).

So it's not about high or low resolution screens (it's just Windows/Apple), it has nothing to do with physical reality (except the 72 on that one rigid Macintosh screen in 1984: these were dots per inch on screen) and best of all, it's only for text fonts.

emalvick · 04-03-2009, 12:08 PM

Originally Posted by Jim Royal

Emalvik: If you were to print your 2MP images (which had a setting of 72 dpi) at the size of 4x6, they would look exactly the same as printing a 2MP image with a setting of 300 dpi at a size of 4x6.

The DPI value inside the file is only a suggestion as to how software should handle the file, for example, how the photo would be imported into a desktop publishing application.

DPI is meaningless without also referring to printed dimensions. A 2 MP image printed at a size of 4x6 actually has a printed resolution of 300 dpi. DPI is meaningless until the photo is actually output onto paper. A 2MP image printed at 72 dpi would be 25 inches across.

I understand that... My point was why bother putting 72 dpi into an image in the first place, which confuses plenty of people. Nothing really needs that value, but that is especially the case of monitors, which apparently it matches up with (the 1984 example posted), and as just shown that even varies. I only say they should put 300 dpi into it by default because for the person who doesn't know better, 300 dpi gives a better indication of a real printed image size than 72 dpi, which I bet very few people purposely use.

*graphicgr8s* · 04-03-2009, 02:33 PM

Originally Posted by khardur

hah.

I wasn't quite so harsh on them as you would be. They've been working exclusively with 1-bit line art and fonts for their entire graphic lives, and for those the requirements are much stiffer than with printing photos. So I can understand why they were confused.

Yeah I'm pretty bad. I don't think I could work for me. I get people that come in and put 2 spaces after a period. So long, don't let the door hit yopu on the way out. I've been in this business way too long. I need to retire but I am not old enough nor wealthy enough. I need to hit lotto. Problem is I would still do graphics work. Here's one for you. I get "designers" coming in and they want 2 spot colors. Did you do it in Pantone colors? Yes. File is CMYK with no spot channels. Try talking to them about it and they have no clue what a spot channel is or how to create it. And these are the "pros".