How far away should you sit from your screen? How large can you print your photos? Why is stacked sensor better? There’s more to those pixels than you might think.
The retina of our eyes consists of millions of light-sensing cells, individual light-detecting points called rods and cones. Each eye has about 576 million, with bars detecting grayscale images and cones picking up color. The cones stop working in low light, so you can’t see red roses and blue violets at night. There is also a third type of cell called photoreceptor ganglion cells, which are not involved in vision but regulate your iris and circadian rhythms. They go hand in hand with the exposure-adjusting light meter in your camera.
That’s a lot more photoreceptor cells in your eye than the equivalent photoreceptor cells on your camera’s sensor. However, that high resolution is mainly concentrated in a small area in the center of your retina, the fovea, and beyond, the resolution is not so great in peripheral vision.
You can check this with your own eyes. Gradually move closer to your monitor or TV. You will see the individual pixels that make up the picture at some point. However, you can only see the people directly in front of you.
The distance at which you can see the pixels will vary depending on whether you have a 1080p HD display or a 4K display. Therefore, the viewing distance should depend on the monitor you are using. Sitting too far away you can’t resolve all the details in the image, too close you’ll see the pixels.
For a 1080p HD display, the viewing distance should be about three times the height of the screen.
I’m typing this using a 24″ HD monitor, so the height of the screen is about 11.8″. So, ideally I need to sit about 35.4″ away from the screen. For a 4K monitor, I should place it 1.5 times the height of the screen, 17.6″.
For an 8K display, we need to sit still closer to work out all the details. If my screen were the same size as it is now, I would just need to be 9 inches away to work out all the details. However, I won’t be able to see the entire screen at that distance. Therefore, that solution will be lost to me. Before rushing to buy the latest 8K TV or monitor, you may want to consider how far away from your chair and therefore, how big the screen should be. Otherwise, you won’t get the full benefit of that solution.
Those measurements are approximate measurements to illustrate a point. My monitor is wall-mounted on extension stands, and I move my office chair around. Therefore, I was never exactly 34.4” from the screen. Furthermore, it also assumes that we have perfect eyesight. As we age, most of us experience a decline in vision, not only in resolution but also in dynamic range.
I usually use 300 dpi or dots per inch for printing. That means a 1” x 1” square will have 300 x 300 = 90,000 points, more than what your eyes can perceive. Accordingly, the image looks sharp. If we reduce that to 85 dots per inch, you’ll see those dots; the image will look blurred. If you’re old enough to remember newspapers and comic books where the image consists of tiny dots, that’s the resolution that offset printers are most used for. However, like your computer monitor and TV, the image is supposed to be viewed from a reading distance, so the image is clearly visible.
If you scan a photo of that newspaper and then print it at a larger size, those dots will appear larger and further apart, so you need to stand further away to discern the details. The same goes for low-resolution photos. If you try to zoom it in too far, the image will be blurred and appear soft. Take a few steps back and the image zooms out in your field of view. It looks sharp again. This is something worth knowing. If you have a blurry photo you want to share, it will look sharper if you reduce the size.
Billboard printers know this. That’s how they make huge prints of images from cameras that are much lower resolution than they are today. People driving past them won’t get that close and, therefore, cannot 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 20” x 30”. However, on the Whitewall blog, 10 MP and up they can print up to a maximum size of 106” x 71” (270 x 180 cm). That makes a mockery of the entire race for more pixels than ever before. Many of us would be better suited to lower resolution cameras with lower pixel density. That means each photodiode – the light-receiving part – on the sensor will be larger. Therefore, it can collect more photons, so the signal-to-noise ratio and dynamic range will be greater.
New stacked sensors, such as those found in Sony Alpha 1the Nikon Z 9the Canon R3and OM System OM-1 much more efficient. In very simple terms, on traditional sensors, millions of light-gathering photodiodes reside with their associated transistors to process the resulting electrical signal. On a stacked sensor, the transistor is underneath the photodiodes. Thus each photodiode can use that space and is much larger.
This means that the sensor stacks up more like the retina in your eye, where the bipolar and ganglion cells, which act like transistors, are behind the rods and cones.
This new technology also allows for much faster image capture. The Z 9 and Alpha 1 can achieve 20 uncompressed raw frames per second (fps), the R3 achieves 30 raw fps, while the OM-1 can shoot uncompressed raw files up to 120 fps second; a benefit of a smaller sensor.
Going back to the photoreceptors in your eye, the color-detecting cones are concentrated in the fovea. The sticks perform better in low light. They are more concentrated in the periphery. As a result, you can see things from the corner of your eye at night that you can’t see when you look directly at them.
There are three different types of color detection cones. L cones detect long wavelength red light, M cones detect medium wavelength blue light, and S cones are sensitive to short wavelength blue light. Approximately how many green cones are there as well as red and blue.
The combination of two parts green with one part red and one part blue is mirrored on the sensor in your camera.
Each photodiode has a light filter that absorbs light in one light band and reflects it in another. Since more of the green filter will reflect red light, your sensor will appear more red.
I hope you find that interesting. A little understanding of how those microscopic dots work can make a big difference to the way we work with our photos. Perhaps you have some useful information regarding resolution, image sharing and printing that you can share with me. Please do so in the comments below.
