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07-27-2012, 04:14 PM   #1
KnifeMaker
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Upping Resolution

I have a Pentax istDL that I got second hand and have been using it successfully enough for my web site. I 'play' with settings and don't know a thing about digital photography, having taken my last photog class 40 years ago. My "problem" is that a magazine wants to include some of our products in an article and wants some photos with white backdrop. Took some, and they looked fine to me on the computer, but they said they need 300 resolution and all my photos are 72 resolution. I have used *** and RAW settings, but get same reading of 72 resolution when I look at "properties". Can anyone tell me what I can do? I use only Picasa to crop/edit etc.

07-27-2012, 04:56 PM   #2
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DPI is a print setting that's not really associated with what comes out of your camera. If you currently have a 72 DPI image, you need to upsample it by about 5 times to get 300 DPI. In simpler terms, all you have to do is increase the width and height of the image in picassa, and the photo's resolution will go up.

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07-27-2012, 07:21 PM   #3
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DPI, or more accurately PPI, has no direct, innate, correlation to the image size in pixels. Pixels are pixels.

The only time DPI/PPI comes into play is when you are working with prints and measuring the desired photographic print size in inches.

If you have a digital image file that is 4500 x 3000 pixels, that will produce a 15 x 10 inch print if the printer is set to 300 DPI.

To create a bigger print from that image you will either have to use a lower DPI setting on the printer, or upsample the image to maintain the same DPI density...

150 DPI would allow you to make a 30x20 inch print from that 4500x3000 image.
Resampling the image to 9000x6000 pixels would allow you make a 30x20 inch print at 300 DPI.
07-27-2012, 10:43 PM   #4
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QuoteOriginally posted by KnifeMaker Quote
Took some, and they looked fine to me on the computer, but they said they need 300 resolution and all my photos are 72 resolution.
Is your magazine editor telling you this, or are you just going by the meaningless number stored in the Exif? Hopefully anyone running a magazine knows that number is meaningless. The actual DPI figure is not something you can store in a file - it is something that you calculate each time you make a print. Literally, like the term DPI (dots per inch) implies: numer of dots divided bu number of inches. Your DL records images about 3000 pixels wide. If you print it 10" wide, that's 3000/10 or 300 DPI, regardless of the meaningless number in the Exif. So as long as you print it smaller than 10", your image will be the required resolution. The image will only be 72 DPI you happen to print it 3000/72 or about 40 inches wide.

07-28-2012, 08:16 PM   #5
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I, too, find it odd that a magazine's photo editor would tell you this. This person is presumably a professional and should know that the number is meaningless in regards to the image file. It is only meaningful to a printer.

As Marc explained, if your image is 3000 pixels on one side and you print that side on a 10 inch print, the printer will print 300 dpi.

I'm not sure about your camera, but my K10D has no setting for dpi. When I display the EXIF info, there are two settings, "X RESOLUTION" and "Y RESOLUTION" that may be dpi. I've never paid the slightest attention to it, and I've printed up to 16 x 20 prints.

If the editor really, really wants your image to say 72 dpi, you can load and resave the image, using one of the popular photo editors. Most of them let you set the dpi value. There is also a program called exiftools that can change the various exif values directly on the image.

Now, the editor may be telling you, not very artfully, that the 6MP maximum resolution from your camera is not sufficient and that they require 10MP or more.
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