Back to Basics: Resolution Simplified, Part 1

By Arthur H. Bleich–

Resolution goes hand-in-hand with almost every aspect of digital photography– from image capture to the final print. If you want your photographs to be the best they can possibly be, it’s necessary to have a basic understanding of it.

At first, it may seem confusing because many who try to explain it often use the wrong terminology or throw lots of numbers around which only makes things worse. This is my shot at making it easy to grasp by trying to get it down to the bare essentials.

 Camera Resolution– Measured In Pixels

Unlike conventional cameras that require film to record pictures, a digital camera’s imaging surface is made up of tightly packed rows of tiny, light-capturing electrical elements (think of them as miniature lenses). When an exposure is made, they capture light and color information which is then converted into the squares (pixels) that form an image which is then saved to a memory card.

sensor-sizes-on-two-cameras

Two cameras with different-sized sensors, but capable of producing the same number of pixels. Camera resolution is described by the total number of image pixels it can produce– not by pixels-per-inch.

The more pixels the resulting image has, the higher its resolution will be– resulting in a photograph with excellent detail. In rough terms, think of low and high resolution as gravel compared to sand; one’s coarse, the other’s fine.

Very early digital camera sensors could only yield low resolution pictures– typically made up of 640 horizontal by 480 vertical pixels for a total of 307,200 pixels (arrived at by multiplying the two dimensions).

As technology improved millions of light-capturing sites could be embedded in sensors and the Megapixel (MP) age evolved. So a camera rated today, say, at 16MP will have a sensor that can capture 16 million pixels worth of information to form a single image.

Camera sensors of different sizes can produce pictures that have the same number of pixels. So if you were to measure the pixel potential of each camera sensor by the inch, the number would vary. That’s why digital camera resolution is always expressed in terms of the total number of pixels it can produce, not in pixels-per-inch. On the other hand, measuring image resolution when printing,  is a whole different ballgame.

Print Image Resolution– Measured In Pixels-Per-Inch (ppi)

Unlike camera resolution, that measures pixels as a fixed number, image resolution is measured in pixels-per-inch (or ppi) and changes with the size of your photo.

For example, imagine a 4×5-inch digital image on a piece of rubber. If you stretch the rubber to an 8 x 10 inch size, each of the pixels in the image gets bigger. If you keep increasing the size of the photo by stretching even more, pixel sizes will continue to increase until you can see each individual pixel, resulting in an image that looks jagged and blocky.

To look at it another way, it’s like viewing solders in a tight formation from the air. They all look nicely packed together. But if they begin to spread out to occupy a larger space, their number stays the same but you begin to see the more space between them.

garden-sharp

This image looks fine when printed at a moderate size. There are enough pixels-per-inch to give it smoothness.

Let’s say that at 4 x 5 inches, 300 pixels were lined up along each inch of the rubber print, resulting in 1200 pixels on the 4-inch side (4-inches x 300 pixels) and 1500 pixels on the 5-inch side (5-inches x 300 pixels).

If you stretch the image to 8 x 10 inches, the pixels get bigger allowing only 150 of them to fit along an inch of space. Nevertheless there are still the same 1200 pixels on the 8-inch side and 1500 pixels on the 10-inch side– only the size of the print has changed making each pixel bigger and easier to see.

So the total number of pixels stays the same, regardless of the image size, but the number of pixels-per-inch (ppi) becomes less as the image size increases and vice-versa.

Here’s the bottom line: Small prints of the same photo will have more (and smaller) pixels to the inch ( and thus a higher ppi number); larger-sized prints of the same photo will have bigger pixels and less of them to the inch (a lower ppi count).

garden-pixelated

When the entire image (or part of it as shown here) is greatly enlarged it begins to disintegrate (or pixelate) because there are not enough pixels-per-inch to give it smoothness. It needs a higher ppi value (more pixels-per-inch) to achieve better quality.

Generally speaking, you need more pixels-per-inch when printing large photos or you will begin to see the image begin to break down into individual pixels instead of appearing smooth. But you don’t necessarily need a camera with an ultra-high pixel count. A camera with as few as 6MP (or even less) will yield an image with enough pixels to output excellent 11×14-inch full-frame prints on your printer.

However, if you want to print very big images or frequently crop your images to blow up just part of them, you’ll need a higher resolution camera to give you an adequate number of pixels-per-inch so that individual pixels won’t begin to show and mess up your image.

In Part 2 we’ll discuss printer resolution (measured in dots-per-inch), how to add more pixels if you need them and what the best settings are to use when you print. 

 

 

18 Comments

  1. These articles have really helped me understand camera and printer resolution.
    If a full frame sensor and a partial frame sensor had the same MP would you expect the output quality to be the same?

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    • Not necessarily. The light-capturing elements on the full-frame sensor would be larger and thus able to produce more dynamic range and better low-light capabilities. In practical terms, though, you might not notice the difference between, say, full-frame and APS. But you probably would between full-frame and much smaller sensors especially if you did huge blow-ups or cropped and enlarged a tiny portion of the image.

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  2. This is a great explanation in my opinion. Agree there are a lot of factors involved in producing a good print. I find this article so interesting because I used to have arguments (discussions – LOL) with a co-worker about how having a camera with more MP is going to produce better quality photos. Obviously it also depends on what size of print you are wanting to print at.

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  3. Thanks for the great article. In reading some of the comments, it became clear that some are “purists”. That’s OK. But as President Obama has been saying, Come on, Man… Photography is an Art form in my opinion. Having said that, grab your camera, get out and take pictures. The printed result for the majority of us is for our pleasure. And hey! Use Red River paper as it is great and the support is awesome!

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  4. Pixels do not have a standard size. It’s your device that determines the quality of the image that you view by displaying or printing so many of them. While your camera may capture millions of pixels, the number of pixels you can actually see on your monitor is determined by your monitor’s hardware and software, not by how many are actually in the image. This is usually expressed as pixels per inch. Most computer monitors display images at 72 pip to 96 ppi. The LCD screens on small cameras may display less. That is not saying that pixels in the image are lost or not there or cannot be printed. It’s saying that the monitor’s hardware and software determine how many pixels are being displayed.

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  5. Per the article camera sensors of different sizes can produce pictures that have the same number of pixels. Does this mean that a sensor pixel is not an absolute unit when it comes to size?

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  6. While I do understand that this article is meant to explain how pixels relate to prints, I feel that the author has done us a disservice by causing many readers to believe that pixel count is the key to quality enlargements. Critical focus and proper exposure are far more important than pixel count in a finished print. After nearly 60 years of photography with everything up to and including 8×10 view cameras I can tell you that even an 8MP camera can easily produce 16×20 inch prints with stunning quality when they are tack sharp and properly exposed. Yes I do most of my shooting with a 36MP Fx format camera these days, but let’s not confuse pixel count with what is required for a great enlargement.

    Post a Reply
    • Pixels-per-inch IS the key to quality enlargements. And you also have to have a minimum number of camera pixels to begin with. You would not be able to make a good 16×20-inch print with an early 1MP camera no matter how good your technique was because there just aren’t enough overall pixels to make that possible. You might be able to squeak it with interpolation but it would never be as good as if you had had more pixels to start with.

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  7. I know this article is about printing resolution, but I hate to see Megapixels become the new term for camera sensors because it misleads the consumer; that is, to expect a measure for perceived detail to be directly related to total pixels. Of course there is a relationship, but resolution would be better understood to have a relationship that is the root of Mp. For example, going from 16Mp to 20Mp is a 25% increase in pixel count, while the increase in resolution would be the root of Mp; i.e., the root of 1.25 or 1.12, that is, only a 12% increase in what to expect for perceived detail.

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    • The above comment makes the basic subject unnecessarily complicated by splitting technical hairs. Nobody said the relationship is linear. All things being equal, a 20MP sensor DOES provide more resolution than a 16MP sensor, albeit by a square root rather than linear ratio. However, in real life, things are rarely equal. The size of each sensor element, lens quality and personal technique all affect image sharpness. With that said, pixel count remains a valid starting point for comparison.

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  8. Fantastic, thank you!!

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  9. What’s a full frame print?

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    • A full-frame print is one that has not been cropped and therefore contains ALL the pixels that were in the captured image. Of course a full-frame print can be small or large. So to be more specific, a quality 6MP camera (such as the example I mentioned in the article) has enough total pixels in each image to produce acceptably sharp 11×14-inch prints. If you output a print larger than that size or attempt to blow up a small section of the image to produce a large-sized print, it may begin to fall apart (or pixelate).

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  10. Thank you, so much. This is the first explanation that really takes me forward after many years trying to understand. Looking forward to Part 2. Chris

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  11. Excellent and concise explanation of resolution. Simple enough for me to understand.

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  12. Lucid and extremely helpful exposition of camera resolution. Wish I’d read this years ago!

    Looking forward to part 2.

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  13. Very clear explanation. Thanks

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