Understanding Image Quality on the MV32

MV32 Sensor Resolution

Compared to the previously described image resolution options the MV32 has a differently sized sensor. In the image below, you can see that the sensor of the MV32 is composed of 3840 x 2160 pixels = 8294400 pixels = ~8MP. Note that this sensor has a 16:9 aspect ratio. However, a 360-degree camera will form a circular image, which is best enclosed in a 1:1 aspect ratio. To obtain this, the image can theoretically only utilize at most 2160 pixels in both horizontal and vertical directions. 

In conclusion, although the MV32 has an 8.4MP sensor, the maximum number of pixels used for the MV32 would be 2058 x 2058 = ~4.2MP effective sensor resolution, which is comparable to the 4MP sensor resolution for the MV12/22/72. Still, this does not imply that the quality of the same subject as viewed through both cameras will be comparable. The field of view of the MV32 will drastically affect how much detail the camera can see. The following section uses the concept of pixels-per-foot (PPF) to demonstrate this.  

Horizontal Pixels

You can improve your PPF by increasing horizontal pixels below. You can do this by using a higher image resolution. The horizontal pixels for each image resolution available on MVs are underlined below.

FoV Width

FoV width is a result of the camera’s FoV, which is dictated by its lens focal length. It is essentially the physical distance that will be captured by the horizontal pixels in the image resolution. While the MV32 cannot be adjusted to optimize for this, you can use optical zoom on the MV22 and MV72 (or select the narrow model of the MV12) to obtain smaller field of view width.

For example: This image is a 1080p image, so the horizontal pixel width is 1920. One can measure the FoV width by finding the distance between something at the far left of the image (for example, the yellow pots on the left of the image below) up to something on the far right of the image (for example, the black legs of the chair on the right side of the image). Note that PPF is in feet, so by converting 10 meters to 32 feet, the PPF of this image is about 1920 pixels / 32 feet  = 60 PPF. 

Example PPFs

Here is a set of images with different PPF values.

Notice how the same distance produces different PPFs in these examples, and especially how the PPF is much smaller for the fisheye cameras. A good rule of thumb is that faces are usually distinguishable around ~50 PPF, so if you want that level of detail, the fisheye camera might not be enough.

Calculating PPFs

It is sufficient to understand the relationship between PPF, resolution and FoV to conclude that the MV32 image quality will often be inferior to that of other cameras. 

However, in cases were you have a target PPF, this section below shows how you can calculate PPFs. You can then work backwards and determine what camera would be sufficient.

For example, a nice rule of thumb is that faces are usually distinguishable around ~50 PPF and you would like to see if the MV32 would provide sufficient detail for subjects around the main area of the camera. 

1. What is the image resolution?

   • Let’s assume you are going to use 1080 horizontal pixels. 

2. What is your target PPF?

   • 50PPF

3. Compute the ideal FoV width.

   • 50PPF = 1080 / FoV width, so FoV width = 1080 / 50 = 21.6 feet

4. Compute the FoV width you can obtain with the MV32 and compare. 

   • It is difficult to directly measure the field of view width. However, if you are able to use a measuring tape to estimate this, you can use that.

   • However, it may be simpler to use the distance of the subject from the center of the camera to estimate this FoV width as shown below.

     • For normal cameras with a triangular field of view (MV12, MV22, MV72), the FoV width can be calculated accurately using trigonometry (fun!) but is usually estimated as equal to the distance from the camera for normal cameras and half for super telephoto cameras (as in the example on the next page).

     • For 360 degree cameras with a circular field of view (MV32), the FoV width is the circumference (2*pi*radius), where the radius is the distance from the center of the camera (see the diagram on the next page that illustrates this). This means that PPF decreases at a rate of 2*pi for fisheyes. 

       • At the same distance from the camera (for example = 1), the resulting PPF can be up to ~6.28 times lower for a 360-degree camera (2*pi = 6.28) compared to a normal camera.

Let’s suppose we care about capturing enough detail for faces of people at the coffee bar, 15 feet from the camera. This produces a FoV width of 94.2 feet. This is larger than 21.6, so the MV32 is likely not going to provide the right amount of detail. However, if the objects are 21.6 / 6.28 = ~3.4 feet away, it should be sufficient. Alternatively, you can use a camera with a smaller field of view, that can produce a FoV smaller than 21.6, as in the MV12N below.

[BETTER]  MV12N, zoomed into the coffee bar (PPF = ~128)	MV32, zoomed into the coffee bar (PPF = ~22)

With this knowledge, you can make better judgments about the level of detail that the MV32 can provide for a particular use case.