Walgreen's Photo Developing & DPI

leerkeller

macrumors member
Original poster
Nov 1, 2011
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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?
 

Bending Pixels

macrumors 65816
Jul 22, 2010
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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.
 

leerkeller

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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.

Yahoo! Answers

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Does DPI affect JPEG file size?
Does the DPI have any affect on the size of a saved JPEG?

Example: If I have a JPEG file that is 800x600 and 72 DPI will it take less storage space than an 800x600 300 DPI image?
6 years ago Report Abuse

imadrian...
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DPI stands for "dots per inch", which lets you know what the pic's resolution is going to be. It is not a file type like JPGs are. So a 300 DPI image is going to take quite a bit more space than a 72 DPI pic because there is a lot more info in the file.

Good luck!
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fhotoace

It will take up less storage space however ... The only reason to change the DPI on a JPEG file is to make it smaller for use on the Internet (50k or less) or for sending out as an attachment to an email (100k or less). The original 300 DPI image is what you need to make photographic prints. If you are running out of hard drive space, you are better off saving those images to a CD.

All the camera manufacturers are rushing to make bigger and better digital sensors and as a result the image file sizes are getting larger (6 megapixel camera raw file = about 10mb, 10 megapixel camera raw file = 16mb).

After a shoot I always upload the images from my camera to my computer (1.4 terabytes [1400GB] of hard drive storage) and then make a CD or DVD depending upon how many images I captured and whether they were JPEG only or RAW + JEPEG). That way if I am tired and accidentally overwrite an original file, I have back up.

Hard drives are so cheap now ($79 for a 300gb drive) and DVD-RW drives for under $70 there should be no reason to reduce the quality of your original images.
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?
 
Last edited:

c1phr

macrumors 6502
Jan 8, 2011
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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?
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.
 

leerkeller

macrumors member
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Nov 1, 2011
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Baltimore, MD
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.
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.
 

ChrisA

macrumors G4
Jan 5, 2006
11,609
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Redondo Beach, California
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.


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.
 

leerkeller

macrumors member
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Nov 1, 2011
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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?

from
http://www.vsellis.com/understanding-dpi-resolution-and-print-vs-web-images/
Understanding DPI, Resolution and Print vs. Web Images
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BY SCOTT ELLIS 78 COMMENTS
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Why should you care about understanding DPI & Resolution? Because if you are going to print something (particularly of quality) or are ever tasked with optimizing images for the web, knowing a few basics will save you a lot of time and give you the best results.

Alternatively, if you ever hire someone to develop print materials for you or build you a website, they’ll likely have requirements you won’t understand and not everyone is good at explaining them.

Read on for a simple explanation of what you need to know.

It’s important to begin with a good picture which means the highest resolution and image dimensions you can get. When it comes to source images, bigger is better, because you can go down in size but not up without losing quality.

I use iStockPhoto.com for stock images and take a lot of my own pictures. If you are looking for resources to help you improve your own pictures take a look at Photo Nuts & Bolts.

Definitions:

DPI: Dot’s per inch. The number of dots or pixels in a single inch. The more dot’s the higher the quality of the picture (more resolution, more sharpness and detail,… ).

Resolution: The easiest way I can explain resolution is to say that more resolution means an image displays more detail (or is capable of displaying more detail). Higher DPI means higher resolution. Resolution is not “size”, but it’s often confused with it because higher resolution images are often bigger, but that doesn’t necessarily have to be the case.

Print: 300dpi is standard, sometimes 150 is acceptable but never lower, you may go higher for some situations.

Web: 72dpi or 96dpi.

Let’s see it in action…

If you are sending someone images to use for print (again, that brochure you are having made) and they tell you the images are “too small” odds are the resolution wasn’t high enough. The image might look great and huge on your computer but is actually really small when printed out. To add to the confusion, your monitor resolution will also determine how big the picture appears to you when viewing it on your computer.

A monitor set to 800×600 will show an 800 pixel wide by 600 pixel tall image as a full screen image. On a monitor that is 1600×1200 the image will only take up 1/4 the screen. You might have thought it would take up half, but it’s actually going to be 1/2 as wide and 1/2 as tall (so 1/2 times 1/2 = 1/4). Long story short, the image will look much smaller on that screen even though the image is the same size.

Here are a couple of quick examples to show you the difference, no matter what your monitor resolution, it’s all relative!

The first example below has a lot of detail and is at 300dpi (even though the web is 72dpi this works for our purposes)

The second example is at 72dpi but scaled up to the same size so you can see the difference in detail. The actual image would be about 1/4 the size when you go from 300dpi to 72dpi, but at the same height and width is where you can actually see the difference.


300dpi example

72dpi example


Hopefully this has helped you get a little clearer on the differences between DPI, resolution and why if you have someone do something for you in print there will be different requirements than for the web. It’s also why that digital camera with higher megapixels takes better pictures than one with lower (lenses and other factors being equal), because it gives you more resolution to capture more detail.

Another important note about monitors, even though 72dpi is standard for the web, monitors have slightly different resolutions depending how you have the monitor set and how big the monitor is. For example, a 19″ monitor set to 1024×768 will show 70ppi (pixels per inch, monitors use pixels which are square not round but pixels and dots for the sake of this conversation are otherwise analogous). By comparison, a 19″ monitor set to 1280×1024 will have a resolution of 87ppx which means you fit more on the screen and get more detail, but everything looks smaller.

Side bar: image files with higher resolution (more dpi) will also have a bigger file size because they contain more data. Start with the biggest images you can but when putting images on the web they should be set to 72dpi, it’ll save you a ton of bandwidth and they’ll load faster. Yes, they’ll be smaller than the original but should in most cases be plenty big because of monitor resolution (ppi) sizes.

One last thing, don’t confuse “image size” with “file size.” Image size refers to the dimensions of the image while file size is how much space the image takes up on a hard drive (kilobytes or megabytes).

Any more questions on DPI, PPI, Resolution? Ask in the comments and we’ll try to clarify.
 

leerkeller

macrumors member
Original poster
Nov 1, 2011
97
0
Baltimore, MD
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.
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.
 

MCH-1138

macrumors 6502
Jan 31, 2013
448
543
California
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.
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.
 

Laird Knox

macrumors 68000
Jun 18, 2010
1,766
938
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.

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.
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.

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?
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. ;)