The 300 ppi Myth Field Report
by Gary Gray
What is the best resolution to print at? What's the largest good quality print I can make with my xxx megapixel camera?
Time and time again, these questions come up on the internet forums.
Every expert chimes in. Some know, some don't. Some are guessing. Some are responding with what they've read elsewhere.
Traditional wisdom says you print at the native resolution of your camera. In practice, people will often times resize their images for the mythical 300 ppi. I don't know where 300 dpi came from, but that's what you'll hear most often. "DPI" is not the same as "PPI". We're talking Pixels Per Inch.
Is 300 ppi the best resolution to use with an inkjet printer? What is the lowest resolution you can use and still get a suitable print?
For my test image, I've taken a photograph from my catalog, made with a Canon 1DsMKII using a Canon EF 70-200mm f/4 L lens.
Nothing fancy, other than it provides a good range of detail from a fairly sharp lens on a high resolution body.
I've conducted a very simple and basic test using the above photograph. Using Photoshop PS3,
I've re-rezed the image to different PPI settings without sharpening the image and have maintained the 8 x 10 inch aspect ratio.
I've printed a 36 x 30 inch contact sheet from Adobe Lightroom, using no print sharpening and with all 9 images at their resolved ppi's, ranging from 75 ppi up to 416 ppi (native.)
The printer used is a HP Z3100, large format Ink-jet. It is state of the art and in perfect color calibration.
The paper is Premier Photo Luster Micropore, a very good paper, commonly used by large format printers for exhibition grade photographs.
Each file is a PSD formatted file from the original RAW image.
Below is a thunbnail view of the contact sheet containing 9 ea, 8x10 inch images which I'll be using for this discussion.
The resolution of each image is contained in the file name. As you can see, there are 9 images total at the following resolutions.
75 ppi, 100 ppi, 125 ppi, 150 ppi, 175 ppi, 200 ppi, 250 ppi, 300 ppi and 416 ppi (native resolution.)
The process is subjective. I take each photograph and analyze it under a controlled light source using the 416 ppi, native resolution image as a benchmark. My analysis is simply done using a loupe to examine the fine details of each shot and make subjective comparisons for each image. I'll then give my opinion as to what a minimal acceptable dpi would be for my particular setup.
Obviously, you can't see these prints. You'll have to take my word for it.
Looking at the 416 native resolution image, it is crisp and detail is very well resolved on the master 8x10 print. I'm concentrating on the building. Looking at the planks, window and the trees surrounding the building. The rocks and slag on the hillside below the building also give me a good reference point. The detail in the roof of the building is present but approaching saturation.
I began by comparing the 75 ppi image to the 416 ppi image. You never know, I may have underestimated the potential quality at 75 ppi, so I wanted to find out right away.
Results. At 75 ppi, the image, plain and simple, is not very good. To the naked eye, it is fuzzy, as if slightly out of focus and stair-stepping is evident in the sloped tin roof of the old mine building. Right off the bat, it is obvious that an image printed at 75 ppi isn't going to impress anybody. It reminds me of old 35mm enlargements done poorly. The scene is recognizable and the print is representative of the scene, but I wouldn't show it off.
Next up, 100 ppi. A noticeable improvement over 75 ppi, but there is still a visible difference from the 416 ppi print, even with the naked eye. With magnification, the details in the boards in the lower center of the frame are simply blurry but the stair-stepping is greatly reduced from that found in the 75 ppi image.
Next, 125 ppi. Things are looking better. Compared to the 100 ppi print, I'm now seeing a better contrast in small details. The large pine trees are showing much better, the tiny rocks and loose lumber is more crisp looking. Compared to the 416 ppi print, it's not looking too bad but not quite as sharp. The 125 ppi print still appears more soft. It's almost passable though. For a snapshot or something non-critical, I could use it.
Next 150 ppi. At first glance, compared with the 416 ppi print using the naked eye, I can't tell the two apart. Under magnification, you can see a difference. Most notably in the yellow trees behind the old mine building and particularly the yellow tree at the far left-center on the edge of the print. The fine detail in the roof of the building is slightly blurred but present on the lower res image. I could sharpen this image slightly and make it work just fine.
Next 175 ppi. Visibly, it looks identical to the 416 ppi print with the naked eye. Only under magnification can you see the difference and only if you study hard. Mostly, there is a loss of contrast in some fine edges on the lower resolution image. Rocks in the hillside, some of the loose planks, the edges between planks on the building. Very subtile and requiring a very close study. I could hang these two prints on a wall and you couldn't look at them with a naked eye and tell me which was which. With a little sharpening in post processing, you could print all day long at 175 ppi and get a good quality print.
Next 200 ppi. Visibly identical to the 416 ppi print. I really had to look hard with magnification to find a difference. The difference shows up mostly in fine details in shadows and only just a tiny bit. The shadows in the pine trees are where it can be found and only with very close and determined study under magnification. I'd use this print for just about anything if I had too. I feel comfortable with this resolution.
Next 250 ppi. With the naked eye, you can see no difference between this resolution and 416 ppi. Under magnification using my loupe, I can find nothing different in general detail. Tonal graduations are about the same, fine areas in the shadows are the same, edge contrast is identical. It would require a microscope to see a difference.
Next 300 ppi. Same as 250 ppi. There simply is no visible difference between the 416, 300 and 250 ppi prints, either with the naked eye nor with a loupe.
Conclusion...well, I already knew what the conclusion was going to be, as I've made this comparison many times in the past with different photographs. You can get a usable and good quality print down to 150 ppi. With good post processing, the average person isn't going to see what is missing and it would required a very trained eye with a magnifying glass to tell you anything different. In a perfect world, I wouldn't scale my photographs any lower than 175 ppi if I wanted to make prints for sale. This particular image would scale nicely to a 22 x 27 inch print at 150 ppi. With proper sharpening, it would look virtually identical at that size to the same image printed at 416 ppi. Nobody could tell the difference with the naked eye.
So, what does this mean? You may have seen different charts floating around on the internet showing the megapixels of the camera and the quality of the print you can expect at different sizes. Poor, Good, Excellent, these seem to be the most common reference. This means I'm going to give you a chart too. Here's my reference chart. I'm calling a 150 ppi print good, anything above excellent, anything below, poor. You'll have to judge for yourself the quality you get and what you need. What I'm saying here is that with a good quality camera and a good sharp lens, you can expect prints to look good at 150 ppi. Anything more is gravy.
So, if you have a 8 megapixel DSLR (Canon EOS 30D for example), you can reasonably expect a decent quality print at 150 ppi with a print size of about 16 x 24.
If you have a 10 megapixel DSLR (Canon EOS 450D for example), the largest decent quality print size you can expect will be roughly 17 x 26 at 150 ppi.
If you have a 12 megapixel DSLR (Nikon D300 for example), the largest decent quality print size you can expect will be roughly 19 x 28.5 at 150 ppi.
If you have a 16 megapixel DSLR (Canon EOS 1DsMKII for example), the largest decent quality print size you can expect will be roughly 22 x 33 at 150 ppi.
If you have a 21 megapixel DSLR (Canon EOS 1DsMKIII for example), the largest decent quality print size you can expect will be roughly 25 x 37 at 150 ppi.
Keep in mind, these are ball-park figures. You'll hear people tell you they've made 24 x 36 inch prints off their 8 megapixel cameras that look great. We'll maybe they look great, maybe they don't. A lot of this will be determined by the type of image you are printing. You may very well get a portrait shot or other low detail scene to print this large without a discernible loss of quality.
You may be able to do down to 125 ppi or maybe even 100 ppi with some types of images. A lot of this is going to be determined by what the expected viewing distance from the image is going to be. As for me, my expected viewing distance is a loupe. I personally make my decision by what I can see under magnification. If you can't see it with a loupe, you certainly won't see it with the naked eye, at any distance. You can of course re-rez your images to larger sizes using Photoshop. This is tricky business though. I'd recommend rezzing in stages and applying very mild sharpening at each stage. There are a number of tricks for stretching your print sizes, but that's a different matter, one I'll cover at a later date.
Other things that come in to play here are of course, the quality of your original image. Is it sharp and clearly in focus to begin with? What is the quality of the lens used? What is the quality of the printer used? What is the quality of the paper used? All questions that only you can answer when you make your prints or send your images out for printing.
One thing for certain though, using 300 ppi is a myth. You don't need to print at 300 ppi to get a good print and if anybody tells you so, they don't know what they are talking about. You don't even need to play it safe and print at 300 ppi. You're wasting your time and effort if you do so.
For me, this is my approach and it has served me well over the years. Your mileage may vary.