Resolution and Digital Photography

Recently, a publication was offering to use some of my photos. In their instructions they asked me to make sure the resolution is at least 200 pixels per inch with a minimum of 2400 on the long side.

So, what does that mean and how can that make your photography better?

Resolution is a term used interchangeably when describing the sensor in a digital camera, the size of the electronic file, the display, and the hard copy of the image.

Pixels per inch (PPI) is the measurement used for your digital camera, file and display; while dots per inch (DPI) is the term used when referring to a physical reproduction of you image, such as a print or magazine.

For example, if an image is 1000 x 1500 pixels and set to print at 200 PPI, the result will be a 5×7.5 inch print (12.7×19.05 cm). Changing to 100 PPI will provide a larger print, but will degrade the image.

Generally speaking, more PPI allows for higher quality as well as a larger image that can be cropped and modified.

Keep in mind that while more resolution should provide the capacity for larger and higher quality images it can’t, on its own, override other factors such as low quality lenses, camera shake, or poor focus.

Higher PPI means less enlarging, and thus less loss of image quality.

So, how much resolution is enough?

The answer depends on how the image is being viewed.

A computer monitor needs considerably fewer PPI to show the photo, as it only displays 72 PPI. A print from an inkjet printer will require considerably more.

I often keep three versions of an image I am retaining – the original as captured in RAW, a large TIFF format file for printing and a much smaller JPG file for use on the ‘net and for emails.

If you are having your prints done by a lab, ask them what works best for them.

If you are making your own prints, check the DPI of your printer and how many inks it uses. In my case, my printer is capable of 1440 DPI and uses eight inks to create the print.

Dividing 1440 by 8 gives me 180 DPI, which just happens to be the native resolution of the Sigma camera I use, so they are a good match.

Some believe that 360 DPI is the optimum for printing, others think it should be a bit less.

This creates a case where it may be necessary to make a digital file larger than its original capture in order to make larger prints.

This is commonly called up-ressing (“upping” the resolution). It uses a process called interpolation to add empty pixels, and then assigns them colours based on the original pixels around them.

Software such as Photoshop, Paint Shop Pro, Genuine Fractals, and others, is the best way to do this, rather than an in-camera function. Using the bicubic setting when doing so is the pre-eminent method.

The photo of the mallard ducks accompanying this column was up-ressed 200 per cent; then 17 per cent of the total image was cropped out to get the result you see here.

Larger prints are usually viewed from a distance so the eye doesn’t notice these additions.

As in all things, moderation is the key; don’t ask for more than can be expected.

If the resolution of an image is too low, we see the dots that created it, similar to the high-grain images from film days.

The best way to understand resolution is to use your digital camera and your software often, trying out different things. It’ll make a lot more sense if you actually do the things you read about.

A word to the wise: always save your original digital photo in the resolution in which it was initially captured.

Work on copies of that file to try different resolutions and other manipulations, so that your original is always safely stored to recover if needed.

If you have questions, email them to [email protected] or post them after the column at

I look forward to hearing from you.

Happy shooting and remember to leave the environment as you found it.

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