Understanding Image Quality on the MV93

MV93 Sensor Resolution

Compared to the previously described image resolution options the MV93 has a differently sized sensor. In the image below, you can see that the sensor of the MV93 is composed of 4072x3046 pixels = 12,403,312 pixels = ~12.4MP. 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 3046 pixels in both horizontal and vertical directions. 

 

                                                    

 

In conclusion, although the MV93 has an 12.4MP sensor, the maximum number of pixels used for the MV93 would be 2880 x 2880 = ~8.3MP effective sensor resolution, which is comparable to the 8.4MP sensor resolution for the MV63. This still does not imply that the quality of the same subject as viewed through both cameras will be comparable. The field of view of the MV93 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.

 

Resolution	Horizontal x Vertical
720p	1280 x 720 pixels
1080p	1920 x 1080 pixels
1080x1080	1080 x 1080 pixels
2560 x 1440	2560 x 1440 pixels
2112x2112	2112 x 2112 pixels
2880x2880	2880 x 2880 pixels
4K	3840 x 2160 pixels

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. 

For example: This image is a 4K image, so the horizontal pixel width is 3840. One can measure the FoV width by finding the distance between something at the far left of the image (for example, the pink shoes on the left of the image below) up to something on the far right of the image (like the white strip that runs along the length of the wall) . Note that PPF is in feet, the PPF of this image is about 3840 pixels / 10.7 feet  = 358 PPF. 

Example PPFs

Here is a set of images with different PPF values.( All images are taken at 5x digital zoom )

35PPF	48PPF	[BEST] 71PPF

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.( depending on the mounting height)

 

Camera Type	Resolution	Horizontal x Vertical	Distance	FoV width	PPF	Distance	FoV width	PPF
Normal	720p	1280 x 720 pixels	10 feet	10 ft	128	15 feet	~15ft	~85
Normal	1080p	1920 x 1080 pixels		10ft	192		~15ft	~128
Super Telephoto	1080p	1920 x 1080 pixels		5ft	384		~7.5ft	~256
Normal	4MP	2560 x 1440 pixels		10ft	256		~15ft	~170
Fisheye	1080x1080	1080 x 1080 pixels		~63ft	~17		~94ft	~11.5
Fisheye	2112x2112	2112 x 2112 Pixels		~63ft	~33.5		~94ft	~22.5
Fisheye	2880x2880	2880 x 2880 Pixels		~63ft	~45.7		~94ft	~30
Normal	4MP	2560 x 1440 pixels		~10ft	256		~15ft	~170
Normal	4k	3840 x 2160 pixels		~10ft	384		~15ft	~256

Calculating PPFs

It is sufficient to understand the relationship between PPF, resolution and FoV to conclude that the MV93 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 MV93 would provide sufficient detail for subjects around the main area of the camera (depending on the resolution you prefer)

 

1. What is the image resolution?

   • Let’s assume you are going to use 2560 horizontal pixels. 

2. What is your target PPF?

   • 50PPF

3. Compute the ideal FoV width.

   • 50PPF = 2560 / FoV width, so FoV width = 2560 / 50 =  51.2 feet

4. Compute the FoV width you can obtain with the MV93 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 (MV63), 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.

     • For 360 degree cameras with a circular field of view (MV93, 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 below 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 where the camera sign is placed, 13 feet from the camera. This produces a FoV width of 81.6 feet. This is larger than 51.2, so the MV93 is likely not going to provide the right amount of detail. However, if the objects are 51.2 / 6.28 = ~8.15 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 51.2, as in the 63 below.

 

[BETTER]  MV63 (PPF = ~71)	MV93, zoomed in (PPF = ~22)

 

With this knowledge, you can make better judgments about the level of detail that the MV93 can provide for a particular use case.