Picture Quality & DPI Assistance

JuiceMC · Dec 12, 2014

I've taken pictures throughout my life. I was even in yearbook and helped manage the school website in high school. But over the past couple of weeks I've realized I'm far from a pro when it comes to knowing about cameras. I can definitely use some help and guidance from people who are knowledable. That brought me here!

Anyways, let me get to it. I was recently contacted about submitting some photos to a magazine. The pictures they are intested in are of my garden. I have always taken pictures of my garden and I've have always been impressed with the snaps I took. The magazine informed me that in order to have your picture published in the magazine, you would need a couple things. One, you need a camera that is 5mb+. And two, if you want to get on the cover or have a full page you need to have 300+ dpi. I thought I was in luck because my camera says 5M and 2560x1920 resolution.

Honestly, I wasn't sure what dpi even was. I asked and was informed, "dpi means dots per inch, it measures how the image will come out in print, most people use higher for print and lower on websites as on a website it slows the site down and in print if it isn't high enough the picture will pixelate in print and look dotty poor quality."

I sent a group of images to them thinking my images were up to par. The magazine thought that my camera was good enough from the sample image I sent them before I sent the group of images, so I was surprised when I received a message asking if I edited the pictures because they seemed to be lower quality. I let them know I may have cropped some of them, but I didn't edit them any further then that. I looked at the properties of the pictures and the dpi was showing up as 72.000 instead of the 300.000+ dpi I need. Is this due to my camera or an uploading issue?

I took some iniciative to see if I could fix the dpi with a picture editing program, and yes, I can edit the dpi. The only factor of the image that changes is the file size. Everything else remains exactly the same from what I can tell. I'm waiting to hear back from the magazine to hear if editing the dpi to 300.000 fixes the issue, but like I said, I'm waiting...

That brings me to my question(s). Is my issue with low quality due to the dpi, my camera, or another factor?

Thanks in advance! I've been asking my friends all day who know anything about picture editing, but it seems that most of them are thrown off when it comes to having an image printed out.

The_Traveler · Dec 12, 2014

The magazine editor needs a bit of help.
High quality printing is done at 250-300 pixels/ inch so multiply the anticipated size in inches by 300 and you'll know the optimum minimum size your file should be in pixels.
Changing an image from 72 dpi to 300 dpi is done with the editing software and effects the picture not at all.
if the file size changes you are doing something wrong.
Post a link to a full size file so we can see what you are doing.

JuiceMC · Dec 12, 2014

I attempted to use the program Gimp 2 to change the dpi. Gimp 2 is a free photo editing software since I don't have Photoshop.

You want me to post a full size file link. When you ask for that do you mean a picture that is uploaded or one of the pictures with an updated dpi of 300?

JuiceMC · Dec 12, 2014

I read this article and it helped. It made me believe that I can use the pictures I've taken, but edit the dpi before sending it to the editor. In the info below they state to use the programs Photoshop or Irfanview. I tried to use the program I have called Gimp 2. Do I need to attempt it on Photoshop or Irfanview?

300 dpi? No! Pixels, thats's what it's all about

An example:
A 4 MP camera produces (ratio 3:2) photos of about (rounded) 2300 x 1500 pixels.
When made with a Nikon camera, you read: 2300 x 1500 pixels, 300 dpi.
When made with a Canon camera, you read 72 dpi instead.
(With the newest Canon cameras it’s usually 180 dpi.)
These photos are to be sent to the printshop, and both are to be printed in the same size.

The Nikon photo will be accepted because it is 300 dpi, which is according to the demands of the printshop. The Canon photo will be returned because of its resolution, which is too low, and its too bad quality to print. According to the prinshop, this photo doesn’t meet the requirements because the dpi is far too low to get a good print.MADNESS! THIS IS NO EXCEPTION, THIS IS THE RULE

This is because one doesn’t understand what dpi/ppi really is. That photo by Canon has exactly the same quality as the one by Nikon (perhaps it is even better, f.e. a sharper, better exposure, less noise) and can be printed in the same size as that one by Nikon. Because the Canon photo has the same number of pixels. Only Canon chose at random the number 72 to be put in the dpi-box, while Nikon chose number 300 in the same way. Kodak took 230. Another manufacturer chose 180, etc.

But such a number has no meaning whatsoever. You can rub or cross this number out and replace it by another number (as it is a digital data, you can of course not rub or cross it out really, you must do this by means of Photoshop).

And when you change in case of the Canon photo the number 72 into 300 in Photoshop (or Irfanview) (uncheck the resample-box!), you save this photo and send it to the printer, he/she will say: 300 dpi, perfect photo.

This while the quality of the photo hasnt’ been changed at all! Same exposure, same number of pixels, nothing has changed. Only the number of 72 has been changed into 300. I think the printer (or his preparer) could have done this quicker himself.

The_Traveler · Dec 13, 2014

If you have changed DPI only without the file being resized, probably all is well.
If there is a drastic filesize change, it has been done incorrectly.

KmH · Dec 13, 2014

The magazine cannot be printed like a photo is printed using an inkjet printer or a chromogenic printer (C-print) for display in a frame on a desk or on a wall.
Magazines are usually printed using a half or full web press.

Next - for digital photographs it is ppi not dpi.
Digital image files are input files. Or stated another way a digital camera is an input device
Dpi is an output device resolution value.

If you check GIMP 2, I bet GIMP calls it ppi instead of dpi. I know that the industry standard software - Adobe Photoshop - calls it ppi.
Printing a color image using an inkjet printer requires multiple 'dots' to print just 1 pixel.
Making a C-print doesn't involve any dots, but it does involve using light sensitive paper and development of the image with chemicals.
High quality inkjet printers have as many as 12 different colors and each print color nozzle may eject as many as 175 'dots'.
Some inkjet printers advertise output resolution of 9600 dpi.

The pixel dimensions (image resolution) of a digital photo and the assigned ppi (print resolution) define print size.
The greater the ppi value, the smaller the print - if image resolution is constant.

Assuming a typical 8.5" x 11" magazine cover we can then do some basic math to derive some working numbers.
pixels / ppi = inches
pixels / inches = ppi
inches x ppi = pixels

So 11 inches x 300 ppi = 3300 pixels
8 inches x 300 ppi = 2400 pixels

You mention your 5 MP camera delivers photos that have image resolution (pixel dimensions) of 2560x1920
2560 / 11" = 232.7 ppi
1920 / 8" = 240 ppi

That difference in the ppi indicates photos out of your camera do not have the same aspect ratio as an 8.5" x 11" magazine cover.

8" x 232.7 ppi = 1861 pixels

1920 px - 1861 px = 59 pixels that need to cropped away from the short side of photos from your camera so they have the same aspect ratio a an 8.5" x 11" magazine cover.

JuiceMC · Dec 13, 2014

Thanks for all the info guys. I ended up going and buying a higher quality digital camera. I should have the dpi issue now. When I upload the pictures my dpi is over 350. Thanks for the info / advice.