What is pixel peeping and why do some people say should I avoid it?

Question

What is pixel peeping?

Is there a benefit in doing it?

What do I have to keep in mind when I peep my pixels?

Answer 1

What is pixel peeping?

• Pixel peeping can be defined as magnifying an image until individual pixels are perceivable by the viewer.
• Pixel peeping may also be defined as magnifying an image on a monitor until each pixel in the image is displayed using one pixel group (made up of a red, green, and blue sub-pixel) on the monitor. We often call this "100% magnification" because there is a 1:1 correspondence between each pixel in the image file and each pixel group on the screen.

In either case, we are usually magnifying the image so that only a small portion of it can be displayed on our monitor at any one time.

Is there a benefit in doing it?

There can be. When doing image processing, it often can be helpful to highly magnify a portion of the image to see the effect of certain changes in processing instructions (settings). Some of those things include:

• Subtle effects of slight changes in noise reduction settings, for example, are easier to see at high magnifications.
• The effects of sharpening/unsharpen mask settings are also easier to see at high magnification. Care must be made, however, to always check sharpening settings for undesirable artifacts at the desired display size.
• When doing dust deletion or other types of "healing" such as cloning out "hot pixels" or bugs flying in the scene.
• Helping us to see detail when drawing precise masks to process an image in layers.

There are also obvious benefits to pixel peeping when looking at test images to do fine tuning of autofocus adjustments when mating a specific lens to a specific camera.

What do I have to keep in mind when I peep my pixels?

Understand that no matter what high end equipment was used and how well it was shot, nothing will look as good magnified to 100% on a large monitor as it will at a more normal display size. Some folks who pixel peep seem to expect the images they take to look just as sharp and noise free all the way down to subatomic levels of magnification!

Pixel peeping has raised expectations of camera and lens performance to ridiculous levels! But that expectation has also pushed camera and lens manufacturers to improve the performance of their products.

A part of a 24MP image displayed on a 23" HD (1920x1080) monitor at 100% magnification is the equivalent enlargement of a 60x40 inch display size of the entire image! Viewing a 50MP image from a camera like the EOS 5Ds at 100% on such a monitor would be like looking at a small section of a 85x57" display size of the entire image! How often do we critically examine an 85x57" print from a distance of only 18-24 inches (the distance between most people's eyes and their computer monitor)?

Like many useful things, one can take pixel peeping to an extreme that is no longer beneficial to the process of producing high quality images.

• One can make the mistaken assumption that viewing two images from two different cameras with different sensor sizes and/or resolutions at 100% will be a valid comparison. If I view an image from a 50MP FF sensor at 100%, I'm making it twice as wide and twice as tall, with four times the area, as viewing an image from a 12.5MP FF sensor at 100%. If I'm viewing a 20MP image from an APS-C sensor at 100%, I'm magnifying it 1.5X more linearly, and 2.25X more in terms of area, than viewing an image from a FF camera with a 20MP sensor at 100%. To properly compare images from two different cameras, each needs to be magnified so that the resulting overall image size from both is the same.
• One can become obsessed with having a "best copy" of a particular lens. One might buy and sell dozens of copies of a lens until one is satisfied they have a "good" instead of a "bad" copy. Then, when they update their camera body, they discover that those "good" copies on the old camera body are now "bad' copies on the new one because the real difference is in manufacturing tolerances and the way they combine between a specific camera and a specific lens.¹ One might spend so much time on such pursuits that they don't ever actually go out and take pictures!

A few years ago Roger Cicala, the founder of lensrentals.com, wrote a blog entry titled: "This lens is soft" and other myths. At the very end of the entry he later included an addendum which said:

I recently saw the greatest real life example of this ever, in an online forum where the poster states ’Canon’s New XX camera sucks’ (I’m eliminating names so the bots don’t pick this up and repeat it.) He goes on to say he had a body for several years, and a hand picked collection of lenses that he knew were perfect because he’d gone through several copies of each to get the sharpest one. Now he bought a new body and all his lenses sucked, and he’d now exchanged bodies twice and they still all sucked. So here is the perfect example of a person starting with a camera at the edge of tolerance, choosing through multiple selection a set of edge-of-tolerance lenses, and now generalizing that all the new bodies suck. The sad part is the new body has microfocus adjustment and he never even tried it. Just sent copy after copy back to the store.

• Related to this, one can become obsessed with owning the "best" lens for a particular camera mount in a particular focal length, or the "best" camera according to all of the noise on the internet. Even though the 35mm f/2 lens one already has does perfectly well for taking the actual photographs one takes, if there is a new 35mm f/2 model introduced that is "sharper" according to all of the review and testing sites and has IS or some new whiz-bang anti-flare coating, one just "has" to have it - even if one never actually takes any photos that might benefit from IS or the new anti-reflective coating (and maybe even if one's camera holding technique results in so much blur caused by camera shake that the differences in "sharpness" between the two lenses will show no noticeable differences)! The thought that one may come across another photographer who is shooting with a "better" lens becomes absolutely horrifying! One "must" have that better lens! The knowledge that another camera scored higher at DxO Mark than the camera one is currently using can not be allowed to go unanswered! One "must" have that better camera!
• One can become obsessed with owning lenses that have scored the highest when tested making images of flat test charts at relatively short distances, even though one may not plan to ever become involved in taking images of flat objects at relatively short distances. Often lenses that score well in such tests are less appropriate for other types of photography that benefit from different design decisions that don't necessarily require absolute edge to edge sharpness of a flat test chart at a relatively short distance. For example, the rendering of out of focus areas of an image, what we call "bokeh", may be a greater concern. At times it seems that designing a lens that renders very smooth and pleasing bokeh can be diametrically opposed to designing a lens that gives ultimate performance shooting flat test charts at very short distances. The former would be considered a "portrait" lens, the latter would be considered a "macro" lens. Insisting on using a macro lens for portraiture because it is "the best" according to how it shoots flat test charts at relatively short distances may result in portraits that are less pleasing than if one had used a lens designed for the type of image one is trying to make.²
• One can spend so much time hunched over a computer monitor with a magnifying glass that, as this excellent answer by jrista to What is considered "sharp enough" w.r.t the landscape pictures from a DSLR with F16? says, "Pixel peeping, amongst other things like eye fatigue and neck pain, is one that will lead down the deep, dark, endless rabbit hole of IQ Worry!"
• One can tend to blame the gear one uses when the photos one takes are less than spectacular. This can lead to GAS (Gear Acquisition Syndrome). GAS can be expensive and take many dollars over many years before one might, one day, come to one's senses and realize, "It's not the gear."

Related questions here at Photography SE:
Does the camera matter?
When should I upgrade my camera body? (The answer there is just as equally applicable to lenses or entire systems.)
What is GAS and how can I avoid it?

How do I diagnose the source of blurry photos?
How to improve image sharpness on Canon 700D?
Will a lens upgrade from the kit lens give me better colors on my backpacking travels?
Will I see enough improvement moving from EF-S to "L" lenses to warrant the cost?
How can I achieve more clarity in my photos of the moon?
Should I buy a new DSLR or spend the money on a photography course with my point & shoot?

_{¹ Please see Roger Cicala's blog entry at lensrentals.com titled: This Lens is Soft, and Other Myths, particularly the last paragraph! The follow-up, posted about two years later, is also pretty good: “This Lens Is Soft” and Other Facts.
² From a response to a comment to my answer to Is replacing all my Fujifilm gear with this Canon zoom lens an upgrade?: "There are sharper 135s than the Canon that dates back to 1996. But I've yet to see one with a smoother character for portraits. In way too many ways, lens makers have sold their souls to the gods of the flat test charts, even when lenses aren't really meant to be used for flat reproduction work. Flat field lenses (often) do not make the best portraits, but they do get the best scores at DxO. MTF has replaced MP as "the number" around which too many gearheads think everything revolves."}