Seems like the size of our photos shouldn’t require that much thought, right? If Photoshop or Photoshop Elements only had buttons that, boom, made your image a 4×6 or an 8×10, everything would be easy. Unfortunately, it’s more complicated than that. I know this because I had to figure this stuff out for myself once, and because people come to this website every day looking for answers to questions about:
- Photo Resolution
- Maximum Print Size
- Cropping photos
- Resizing photo
- Aspect Ratio
Each of these topics is related to the others, and you can’t understand one without understanding them all. Use the infographic below as a cheatsheet. And if you want more info, read below it for tips, explanations of key terms and links to articles that will deepen your understanding.
Pixel Size – Each photo we take is “born” with a set amount of pixels in it. My camera, for example, is 20 megapixels. That means that each full-size photo I take with it has 20 million pixels.
Print Size – The size that you’d like to print your photo at. For instance, 16×20 and 4×6 are both examples of print size.
Resolution – Resolution ties pixel size to print size. It tells you how many pixels from your digital file end up in each inch of your printed image.
I have 20 million pixels in my photos and I can cram each and every one of them into a 4×6. Or I can stretch them out into a 16×20.
My 20 megapixel photos are about 5400 pixels wide. If I print a photo at 6 inches wide, each inch is 900 pixels wide (5400 pixels divided by 6 inches equals 900). In other words, the resolution is 900 pixels per inch. (Locate your image’s pixel width by going to the Image menu in Photoshop or Elements and selecting Image Size or Resize/Image Size.)
However, if I print that 20 megapixel photo at 20 inches wide, my resolution is 270 pixels per inch (5400/20=270).
Why is resolution important to printing? Take this concept to the extreme. Say that my image is only 1000 pixels wide. If I print it at 4 inches wide, each inch will have 250 pixels in it (1000/4=250). My eyes can’t discern 250 separate pixels across one inch, so the print quality looks good.
However, if I print that same image at 40 inches wide, each inch will have only 25 pixels (1000/40=25). I would be able to see those individual pixels. When our eyes can see pixels, that image is low quality or pixelated looking. To print an image, you need to have enough pixels that those tiny points of detail will be so small that we can’t see where one ends and the next begins. Click here to see a pixel-ly low-resolution photo.
High Resolution – High resolution photos are required for high quality prints. Your printer or print lab will tell you the minimum resolution required. Most printers require between 200 and 300 pixels per inch minimum resolution.
Unless you have reduced the resolution of your image, it is already high resolution, and you can’t, for purposes of this article, increase its resolution. In addition to decreasing resolution using the resizing technique described below, you can also decrease it by saving a file as a JPG while you work. You should save files as PSDs during your edits, and convert them to JPGs only when you need to send to the print lab or post online. Learn more about saving file types here.
Low Resolution – Low resolution photos upload more quickly and display more easily on the internet. They do not print well. 72 pixels per inch is the optimal resolution for posting digitally. We resize in order to create a low resolution photo.
Resizing – Resizing reduces the number of pixels in your photo without visibly removing any part of the photo. (For purposes of this article, you can’t increase pixels in a photo.) We can use the term “Resize” synonymously with “Downsize.”
We resize or downsize our photos to make them easier to share on the internet. Resizing removes pixels to make the photos “weigh less.” They will upload and download more quickly and presumably look better on sites like Facebook that likes to resize photos for us if they are too “heavy.” This article shows you how to create a low resolution file.
Cropping – Cropping reduces the number of pixels in your image by visibly cutting off edges of a photo. We crop in order to recompose or make the image fit a specific aspect ratio. Cutting off these edges deletes all pixels associated with this part of the image.
While editing, I only crop to recompose my image. This means that I only crop if I want to cut out something distracting on the periphery or if I want to change my subject’s place in relation to the photo. For instance, I might want my subject to conform to the rule of thirds rather than being centered. Read this tutorial to learn how to crop in Photoshop Elements.
Aspect Ratio – Aspect ratio is the proportion of an image’s width to its height.
Aspect ratios can come in many sizes. For instance, in terms of aspect ratios, a 4×5 is the same as an 8×10, which is the same as a 16×20. You can print the same image at any of those sizes without cropping. I know they are the same aspect ratio because multiplying 4×5 times 2 gives me 8×10. And multiplying 8×10 by 2 gives me 16×20.
Aspect ratio is the reason that all your glass baking dishes don’t nest inside each other. Even though all of your dishes might be rectangles, the proportions of each side are different. Your longest one might be more narrow than a smaller dish.
Going from one aspect ratio to another in photography requires cropping. Most of our cameras shoot in a 2:3 aspect ratio, which creates the standard 4×6 print. If I want to print my 4×6 at a larger size, I can double it to make an 8×12. But if I want that enlargement to fit in my 8×10 frame, I need to crop off those extra two inches. See this concept in action here.
What aspect ratio should you use for the photos you give your clients? I never change my aspect ratio unless I am about to print the photo. And then, I only change the aspect ratio of the file I’ve uploaded to the print lab. I never change the aspect ratio of the file on my computer. Keeping your photos at their original aspect ratios will give you and your clients maximum flexibility in printing.
Maximum Print Size – Since photos are born with a set number of pixels and you can’t create more, there is a limit on the maximum size at which you can print your photo with good quality. To identify your maximum print width, identify your photo’s width in pixels and divide it by the minimum resolution required by your printer. This will tell you your maximum print width. For instance, if I send my 5400 pixel-wide photo to a printer that requires a 200 ppi minimum resolution, my photo can’t print wider than 27 inches. (5400/200=27). This article contains a shortcut to determine how large your image can print.
Two Important Parting Tips:
- When your print lab tells you to send a high resolution file, they aren’t asking you to change the file. The file is “born” as high res as it’s going to get. They are, however, asking you not to reduce the resolution or downsize the image before sending it.
- The Image Size dialog box under the Image menu in Photoshop or Elements will tell you a resolution for the photo. This number is meaningless for purposes of printing. Regardless of what the resolution field in the Image Size dialog box says, you do not need to change it before printing. If I send a file with all 20 of my megapixels and tell the print lab to print it as a 4×6, the resolution will automatically be 900 ppi because all 20 million pixels are being squeezed into 6 inches across. It I ask the print lab to print it at 16×20, it will automatically print at 270 ppi because those 20 million pixels are going to be stretched across 20 inches.
Whether you use Elements or full Photoshop, the concepts related to photo size work the same way. If you need more help with cropping, aspect ratio or resolution, check out my Photoshop Elements workshop where you can ask all the questions you’d like until it clicks.