RogueStorm Loc: East Sussex, England

I've just read an article on Tom's Guide (www.tomsguide.com) about the size of prints from digital cameras and the correlation between the two. The article went as follows;

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For most people, the highest resolution files they will need will be for the occasional print or photo book. Here’s how you calculate the number of megapixels you’ll need for a printed photograph:
Determine the physical size of your print, such as 4 x 6 inches, 8 x 10 inches, etc. Then, multiply the width by 300, and the height by 300, which will give you the size in terms of pixels. (300 ppi — pixels per inch — is recommended for good-quality prints.) Therefore, an 8 x 10 inch print would be 2,400 x 3,000 pixels.
Multiply the width (in pixels) by the height (in pixels). So for that 8 x 10 inch print, it would be 2400 x 3000, which equals 7.2 million pixels.
Divide the result from step 2 by 1 million, and you have the number of megapixels you need to make a good print. In this case, the minimum resolution you’ll want your camera to have is 7.2 megapixels.
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Using the above calculation I figure that a 9" x 9" print will come out at around 7.29MP. I've chosen a square one to make the comparison below a bit easier.

Working backwards from this, my camera, a Canon 760D, has 24.2 MP; the square root of 24.2 million is (roughly) 4920. Divide this number by 300 and I end up with a maximum print size of around 16.4" x 16.4".

This seems a bit small but it won't be the first time my calculations have gone awry.

Question: Does that sound about right?

I have no desire, or intent to print anything bigger, I'm just curious and continuing my learning process.

Thanks.

jeep_daddy Loc: Prescott AZ

I don't know about that last equation, but the simple matter is that the larger the print, the fewer pixel/inch you need. So a 24x36 or 2 foot by 3 foot image really only needs to be around 200ppi because you won't be standing as close to it when viewing. If you've ever seen a billboard up close, the pixels are very few and far apart but from the road, they look fine. I've even gotten away with 150ppi on some large prints. To see what your cameras pixels are capable of printing at the resolution of 300ppi just look at the exif of any file and do that same math so that you'll know what the native 2x3 format will net you when printing. Your equation showed what a square print would be but cameras have a 2x3 form, not a 1x1 form.

BebuLamar

That sounds about right! If you don't intend to print bigger don't worry. You can print bigger with good result but since you don't, don't worry about it. The 300 PPI was chosen because you can't really print higher than that no matter how many pixels your camera has.

MT Shooter Loc: Montana

It's a "rule of thumb", and a misunderstood one at that. PPI is a sensor measurement and DPI is a printing standard. I have printed hundreds of 24x36 inch images over the years from 16MP Nikon D7000's and they are so sharp you cannot see any pixelization in them even with a magnifying glass! Many samples hang in my store on display for viewing.
That said, the cameras processor, sensor quality, lens used, and operator skill all contribute to the print size capability of any digital image. Also, forget large, sharp prints if you use a cheap UV filter on your lens, just not gonna happen. I have two 44" printers running in my shop and they are operating daily doing large prints for my own sales as well as customers prints and I have yet to have a single complaint of image quality from a single customer.
By the way, the D7000 is 6000x4000 pixels so with your formula the largest print it could yield is 20" x 13.3", and that would be a ridiculous size maximum. I can print that big from a M4/3's camera.

Gary Truchelut Loc: Coldspring, TX

How much difference does it make to print from a jpg or a tiff file? I would think tiff would be better in this case.

GraveyDave

This photo taken with Nikon D300 and a 70-200 f/2.8 lens.
1/400 sec. f/9 ISO 320
The file is 5.36MB and is 488x2848
I was extremely surprised to find this and many others blown up to 4 ft. x 6 ft. in the hanger. You could see every rivet in this test aircraft.
I also shot a billboard for cablevision. The guy I sent it to wanted no more than a 1MB file to receive on his cell.
NO Stepping or ill effects that I, quite honestly, thought would happen under the circumstances so who knows?

camerapapi Loc: Miami, Fl.

I have never agonized about the megapixels of my cameras. The maximum print enlargements I do are 13x19 and none of the cameras I have owned, beginning with the old D100 did ever fail to reach that size.
I am not a good mathematician anyway.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Required ppi is entirely based on the following criteria:

Print size, which implies viewing distance - bigger print, fewer ppi required. The eye's ability to resolve detail diminishes with the distance to the print
Subject - highly detailed or textured subjects generally require a little more ppi than a sunset.
Print surface - a canvas or highly textured fine art paper can get away with less ppi than something printed on glass, metal or a high gloss print.

I have printed and sold 40x60 prints using an uncropped image from a D70S (3000x2000 px) and no one complained about the sharpness, clarity or noise. That would be printed at 50 ppi, which refers to the input resolution of the image before printing. Dpi would refer to the output resolution, or display resolution. Here is an example of one of those images.

For future reference, you might want to bookmark this site:

http://www.photokaboom.com/photography/learn/printing/resolution/1_which_resolution_print_size_viewing_distance.htm

It is accurate, and saves you a lot of head scratching.

(Download)

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Great example! And a nice shot!

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Unless your printer can process 16 bit tif files, probably not much, if any.

Gaddysmom

MT Shooter, "Also, forget large, sharp prints if you use a cheap UV filter on your lens, just not gonna happen;" are you advising us against UV filters, just cheap ones, or, "protective" filters in general? If just cheap ones, what do you recommend?
Thanks in advance.

drizztguen77 Loc: Tualatin, OR

I personally advise against them. I've seen videos where people have tested their ability to protect the lens (by getting old lenses, putting the UV filter on and dropping the lens on an iron rod) and they basically don't protect your lens at all. All they really do is degrade the quality of the picture. Just being careful with your camera and lens to not drop it is a much better option in my opinion.

via the lens Loc: Northern California, near Yosemite NP

Rogue Storm,

Every camera manufacturer sets the dimension size of a print for each of their cameras. This is the size that you will get the very best quality print and provides you with a 1:1 ratio for your print, i.e., no interpolation required to print it (interpolation is a method of constructing new data points within the range of a discrete set of known data points) at 300 ppi. Interpolation means that an algorithm fills in the missing portion of the image when you enlarge it beyond its original, each program may use a different type of algorithm so you may need to find out how your program does this. A general guideline for the best quality print for framing is 300 ppi. If you use the 1:1 ratio you can print at this size. Having said all of that, many images undergo interpolation without any problems. However, if you have an image that is less than ideal, not very sharp, perhaps very dark, lacking sufficient midtones, etc., your image may not turn out ideal when printed larger. When printing larger, using a ppi of less than 300 ppi is considered to be acceptable; your ppi will depend on how large you want your print to be. Adobe routinely sets its software for 240 ppi for all prints, so this is most likely a safe bet when up-sizing a print. The sharpness of the print is also something most people consider when up-sizing, but different people may have different standards for this, as I've seen when viewing finished prints. I have enlarged many a print and used 300 ppi to print and had no problem at all, but I think it's best to use the approach on a case-by-case basis, reviewing your specific print for sharpness, color range, etc. and then determining how that specific print will best print out.

Gaddysmom

Thank you, MT Shooter. I have long realized that the protective value is about nil, but habits begun in high school are hard to break 40+ years later.

via the lens Loc: Northern California, near Yosemite NP

That's what I thought, too, until my tripod fell over in Yosemite recently and the whole thing went down in the brush. I was lucky that the lens was not scratched at all, just smudged heavily. It seems like you just can't win, either way. I know, I know, "don't let go of the tripod." Good advice. If you don't use a uv filter get additional insurance, mine is an add-on to my homeowner's policy and is 0 deductible and I almost had to use it!