The Surprising Facts About Pixels and How They Affect Your Photography

How far should you sit from your screen? What size can you print your photos? Why are stacked sensors better? There’s a lot more to these pixels than you might think.

The retina of our eyes is made up of millions of photoreceptor cells, individual light-sensing points called rods and cones. Each eye has about 576 million, with rods detecting a grayscale image and cones picking up color. Cones stop working in low light, so you can’t see roses are red and violets are blue at night. There is also a third type of cell called a photosensitive ganglion cell, which is not involved in vision but in adjusting your iris and circadian rhythm. These run parallel to the light meter that adjusts your camera’s exposure.

That’s a lot of photoreceptor cells in your eye compared to the equivalent photoreceptors on your camera sensor. However, this high resolution is mostly concentrated in a small area in the center of your retina, the fovea, and beyond that the resolution isn’t that great in peripheral vision.

You can test this with your eyes. Gradually move closer to your monitor or TV. You will see the individual pixels that make up the image at any given time. However, you can only see those directly in front of your eyes.

The distance at which you can see pixels varies depending on whether you have a 1080p HD or 4K display. Therefore, the viewing distance should depend on the monitor you are using. Sit too far away, you can’t resolve all the details of the image, too close and you will see the pixels.

For a 1080p HD screen, the viewing distance should be approximately three times the height of the screen.

I’m typing this using a 24 inch HD monitor, so the screen height is about 11.8 inches. Therefore, I should ideally sit about 35.4 inches from the screen. For a 4K monitor, I would need to be 1.5 times the height of the screen, 17.6 inches from the screen.

For an 8K monitor, we have to sit even closer to work out all the details. If my screen was the same size as the one I have now, I would only need to be 9 inches from the screen to resolve all the details. However, I couldn’t see the whole screen from that distance. Therefore, this resolution would be lost on me. Before you rush out to buy the latest 8K TV or monitor, you might want to consider how far your chair is and, therefore, how big the screen should be. Otherwise, you will not get the full benefits of this resolution.

These measurements are approximations to illustrate a point. My screens are fixed to the wall on extendable brackets and I move my office chair. Therefore, I’m never exactly 34.4 inches from the screen. Moreover, it also assumes that we have perfect eyesight. As we age, most of us suffer from some degradation in vision, not only in resolution, but also in dynamic range.

I generally use 300 dpi, or dots per inch, for printing. This means that a 1″ x 1″ square would have 300 x 300 = 90,000 dots, far more than your eyes can perceive. As a result, the image looks sharp. If we reduced that to 85 dots per inch, you would see these dots; the image would look pixelated. If you’re old enough to remember newspapers and comic books where images consisted of small dots, this was the resolution most used by offset presses. Yet, like your computer monitor and TV, the images were meant to be viewed from a reading distance, so the images looked well defined.

If you scanned this newspaper image and then printed it at a larger size, these dots would appear larger and further apart, so you’ll have to stand further back to make out the detail. The same thing happens with low resolution photographs. If you try to enlarge it too far, the image becomes pixelated and looks soft. Take a few steps back and the image shrinks in your field of vision. It looks sharp once again. It is worth knowing. If you want to share a blurry photo, it will appear sharper if you scale it down.

Billboard printers know this. This is how they produced huge prints of images from cameras with much lower resolutions than those available today. People walking past them wouldn’t get that close and therefore couldn’t see the pixels.

So how many pixels do we need to print an image to hang on our wall?

According to an old chart on the B&H website, a 10 megapixel camera can print a 20″ x 30″. However, on the Whitewall blog, from 10 MP they can print up to the maximum size of 106″ x 71″ (270 x 180 cm). This mocks the whole race for ever more pixels. Many of us would be better suited to lower resolution cameras with lower pixel density. This would mean that each photodiode – light receiver – on the sensor would be larger. So it could gather more photons, so signal to noise ratio and dynamic range would be bigger.

Newer stacked sensors, like the one found in the new Sony Alpha 1, Nikon Z 9, Canon R3 and OM System OM-1 are much more efficient. Simply put, on traditional sensors, the millions of photodiodes that collect light sit alongside their associated transistors that process the resulting electrical signal. On a stacked sensor, the transistor sits below the photodiodes. Therefore, each photodiode can use this space and be much larger.

This means the stacked sensor looks more like the retina of your eye, where the bipolar cells and ganglion cells, which act like the transistor, sit behind the rods and cones.

This new technology also allows for much faster shooting. The Z 9 and Alpha 1 can hit 20 raw uncompressed frames per second (fps), the R3 hit 30 fps raw, while the OM-1 can shoot up to 120 fps raw uncompressed; an advantage of the smaller sensor.

Going back to the light receptors in your eye, the color sensing cones are focused on the fovea. Stems work best in low light. They are more concentrated in the periphery. Therefore, you can see things out of the corner of your eye at night that you cannot see when looking directly at them.

There are three different types of color detection cones. L cones detect long wavelength red light, M cones detect mid wavelength blue light and S cones are sensitive to short wave green light. There are about as many green cones as red and blue combined.

This mixture of two green parts with a red part and a blue part is duplicated on the sensor of your camera.

Each photodiode has a light filter that absorbs light in one light range and reflects it in others. Since most green filters will reflect red light, your sensor will appear more reddish.

I hope you found this interesting. Understanding a little about how these microscopic dots work can make a big difference in how we work with our photos. Maybe you have some useful information regarding resolution, image sharing and printing that you can share with me. Please do so in the comments below.

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