Pixels Determine Potential, Not QualityBy IPVM Team, Published Dec 17, 2020, 09:53am EST
However, pixels determine potential quality. In this note, we explain and help you make clearer decisions when selecting cameras.
Demonstrated With Images
Here is a relatively high quality, high 'resolution' image:
It's 161 pixels wide across a small area of 1 - 2 feet, delivering a high ~100 pixels per foot (PPF).
Now contrast this with this low quality, low resolution image:
This is 5 pixels wide and 7 pixels tall, a total of 35 pixels covering the same exact area as the image above (enlarged so you can see it). This image is extremely low quality and you cannot identify it as a human face.
Why? The pixels are being forced to cover areas wider than the details desired. You can see this with the blockiness of the image. Those blocks are the limits of the pixel.
The image calls out 3 of the 35 pixels but you can make out pretty much all the individual pixels.
Now let's increase the pixels / resolution for this image.
More details are being revealed now, and we can recognize that this image is a human. The number of pixels increases from 35 total to 140 and each pixel now can cover a smaller area, with eyes, hair, and mouth visible.
Let's increase the pixels for this scene again, from 140 to 540:
As each pixel covers a smaller area, more features continue to emerge - lips, ears, nose, etc., and we can now make out the subject's eyebrows vs. eyes and roughly see his jawline.
Let's compare two images to see key details in the image improve:
In the former image, the eyes were bigger than the pixels and therefore could not be captured. However, in the latter one, with pixels cover an area smaller than an individual eye, allows the eyes to be captured as dark spots.
Finally, here's four samples ranging from 35 to 2120 pixels covering the same area:
Clearly, as we allocate more pixels to the target, the more fine details my potentially be captured.
The smaller pixel count images could not capture those details because each pixel was covering too large an area for them, regardless of how "good" a camera might be.
Pixels Limits on Quality
A 1080p camera will never capture the fine details of the face of a subject at a 75' wide FoV. It simply lacks the potential, because the pixels will cover too large an area relative (~25 PPF) to how small a face is at the same position.
However, a 4K camera covering that same 50' wide FoV may capture the fine details. It has the potential, because the pixels will be covering small enough areas (~50 PPF).
This potential, though, is a maximum theoretical limit bound by very important factors like:
- Ability to capture in low light scenes, which many (but not all) 4K and 5MP cameras are significantly worse at. See our Super Low Light Surveillance Guide and Color Low Light Camera Shootout.
- Quality of a camera's built-in IR illumination, which varies drastically from model to model. See our IR Surveillance Camera Guide
- Ability to handle wide dynamic range scenes. See our Wide Dynamic Range (WDR) Guide and WDR Camera Shootout.
- Quality of lens, preciseness of focus, and eliminating any potential depth of field problems. See our Lens, Camera Focusing, and Depth of Field tutorials.
- Minimizing compression artifacts / loss of quality. See our Video Quality / Compression Tutorial.
- Angle of incidence of subject to camera (if the camera is too high or the person is looking askew from the camera, more pixels will not help). See our Camera Mounting Height Test.
Quality vs. Pixels
Ultimately, image quality is driven by a half dozen factors combined. While pixel density / pixel count determines the potential quality and the maximum achievable details, those other factors, that are often overlooked and ignored in PPF calculations, routinely and often dramatically constrain the actual image quality achieved.
[This post was first published in 2013 but updated in 2020 for clarity and to reflect changes in camera technology.]]
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