Walgreen's Photo Developing & DPI

Discussion in 'Digital Photography' started by leerkeller, Jun 12, 2013.

  1. leerkeller macrumors member

    Nov 1, 2011
    Baltimore, MD
    Walgreen's has an advertised special of $0.10 per 4"x6" print if you buy 50 or more. I was planning on having about 300 photos printed out. My question arises from the DPI tags on the photos. Just about half have an image dpi of 72, while the rest are 300 dpi. Do I need to go into photoshop and change the tags on the 72 dpi photos to 300 dpi? Since there is no batch function that allows me to change the print size without resampling the image it will take quite a bit of time to modify 150 photos individually. The photos all have a resolution of 4,288 x 2,848. So that leads to my question, will there be a difference in quality or any difference between the photos tagged at 72 dpi vs those tagged at 300 dpi?
  2. Bending Pixels macrumors 65816

    Jul 22, 2010
    Are the 72dpi images also sized at 4,288x2,848? They might print ok.

    I'd suggest running a test print on your home printer using decent photo or heavy matte paper to see how they look first.
  3. leerkeller, Jun 12, 2013
    Last edited: Jun 12, 2013

    leerkeller thread starter macrumors member

    Nov 1, 2011
    Baltimore, MD
    The whole DPI thing makes my head spin. Right when I think I understand it, something comes along to disprove what I learned. Like the Question/Answer from Yahoo pasted below. I thought the DPI value in JPEGs only had relevance in regards to printing the photos and had no bearing on how they appeared on a monitor or their file size. Guess I was wrong on that.

    There is one other issue with DPI that confuses me. Why is it that better quality cameras generally assign higher DPI values to the photos they take. Among the three cameras used in my family the trend appears. Photos taken with my Nikon D5000 DSLR have an image DPI of 300 pixels/inch. My compact Canon Powershot A1100 assigns an image DPI of 180 pixels/inch. Finally my sister's el cheapo Fuji Finepix J30's images have a DPI of 72 pixels/inch. Is there some benefit to having a higher native/default DPI? Does some kind of image degradation occur or is it less than ideal to adjust an image's DPI through software?
  4. c1phr macrumors 6502

    Jan 8, 2011
    Since this is an Apple website, perhaps this analogy will help a bit.

    DPI and PPI (pixels per inch) are very similar, not identical, but let's assume they are for the sake of this comparison.

    If you look at a MacBook Pro and a Retina Pro side by side from a normal distance, the Retina looks a bit better, but they're pretty similar. Now if you pressed your nose into each screen, the Retina would still look decent, while the normal Pro would lose a good bit of detail. (This would be the case with an iPad 2 and a Retina iPad as well)

    This is because the Retina versions have a lot more smaller pixels, so you need to get even closer before the quality of the image starts to break down. The regular Pro (or iPad 2) has less pixels, and the pixels are much larger.

    Photo printers will print around 300 DPI, so a 300 DPI image should print fine to a size up to whatever resolution the camera recorded. An image at 72 DPI would need to be printed at a smaller size, so that the less dense dots in the file can be placed closer together on paper. If you were to print a 72 DPI image really large, you have less dots to work with in the image, so they are much more spread out on the page.
  5. leerkeller thread starter macrumors member

    Nov 1, 2011
    Baltimore, MD
    So will a 72 dpi 4,288 x 2,848 pixel image printed at 4"x6" by Walgreens be visibly inferior to a 300 dpi 4,288 x 2,848 printed at 4"x6" by Walgreens?

    I figure it will take at least an hour to adjust 150 images from 72 dpi to 300 dpi with GIMP. I would like to know if I am wasting my time doing that.
  6. ChrisA macrumors G4

    Jan 5, 2006
    Redondo Beach, California

    NO. All that matters is the number of pixels and the print size. Your prints will be printed at whtever DPI the printer machine can do. The machine will resample whatever file you have to the machine's native resolution. You have enough pixels to suport up to about 700 pixels per inch. But the machine may not be able to do that and you get 30, 400 ot 600 (I don't know which, depends on the machine)

    As soon as you specify a print size the "pixel per inch" tag is meaningless.
  7. leerkeller thread starter macrumors member

    Nov 1, 2011
    Baltimore, MD
    I just read this and I am like getting a headache. It confuses me and runs counter to what I know about DPI. The guy who wrote it seems to be someone who knows what he is talking about and in the 78 comments about the page there are no corrections about the information provided. So is what he says correct?

  8. leerkeller thread starter macrumors member

    Nov 1, 2011
    Baltimore, MD
    Isn't it best to change the photo to 300 dpi at home without using resampling, rather than have them resample the image at walgreens.
  9. MCH-1138 macrumors 6502


    Jan 31, 2013
    Why not try it and see?

    Take one photo and make two copies. Leave one at 72dpi and convert the other to 300dpi. Take the two files to Walgreen and have them printed at 4x6.
  10. Laird Knox macrumors 68000

    Jun 18, 2010
    For the most part you don't have to worry about DPI, PPI or LPI when printing. I am willing to bet that you would get the exact same print from Walgreen's if you set the DPI at 72, 240, 300 and 600 while maintaining the 4,288 x 2,848 pixel dimensions. They are going to use automated software that re-sizes and crops the image to the proper dimensions. In fact, that size image will be a bit over 700 dots (pixels) per inch when printed at 4x6.

    Where you will see the biggest difference is if you use the display at print size option in Photoshop or Lightroom. In that case you need to know the PPI you are printing at and the DPI of the monitor. If you have those set correctly then you will get a 1:1 image on screen at print size. (Incidentally, this is a good view to use when you are sharpening an image for output.)

    When I print off my local printer I set set my dimensions and let the DPI auto adjust without resizing. Typically this will result in a crazy DPI number like 283.6 or 592.4 but it is still a much larger dot than the ultimate resolution of the printer (4800 x 2400 DPI).

    You don't have to worry about the specifics unless you get into offset printing (CMYK). Since an offset print is made by four (or more) individual print processes you run into issues of moire patterns if the registration is off slightly (and it will be). As a result offset printing is done differently and concerns LPI (lines per inch) and screen angles. This is a whole different world of hurt you don't want to get into.

    Bottom line is: Don't stress over the PPI/DPI settings unless the printer demands a certain format. Only then should you re-size your image. Otherwise send them the highest resolution image you have and let them deal with the details. Daily Walgreen's gets 72 and 300 dpi prints. Their workflow will give you the best print they can depending on the resolution of your image file and not the DPI setting.

    If you can avoid re-sampling an image then by all means don't do it.

    Yes and no. If you use "display at print size" in your software then you need three things set correctly: image size (4x6), printer target DPI (300) and screen DPI (often 72 for Mac and 96 for Win but not always and adjusted for screen size). When all of these are setup correctly then you will get a true 1:1 preview of your image.

    Since you generally don't have to sweat the details of DPI too much it really doesn't make a difference in your workflow. Your primary concern is with the dimensions (MP) of the image.

    Apple set the 72 DPI bar with the original Macs. This was the first mass market WYSIWYG system. The 9" screens were 72 DPI and displaying things at 100% gave you a 1:1 view of what would come out of the printer.

    The first (again first mass market) laser printers were 300 DPI. This value has stuck in market even though today's printers are much higher resolution. This is the number most often cited for use when printing.

    Some other companies that make both cameras and printers optimized their camera's DPI settings to match what they felt was best for their printers. 240 is a common value in this regard, but you will find many others as you noted above.

    In closing, if you are using a printing service that isn't giving you the full resolution of your image file regardless of the DPI setting then it is time to find another printer. ;)

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