Logitech C920 Angle of View

I realized today that the Logitech C920 webcam produces images covering a different field of vision (FOV) for the same width based on the height. I was expecting the horizontal field to be the same for a given width but it was not.

Using the command ffmpeg -f video4linux2 -list_formats all -i /dev/video0 to retrieve the sizes of video available lists the same set of sizes for h264 and mjpeg. 640×480 160×90 160×120 176×144 320×180 320×240 352×288 432×240 640×360 800×448 800×600 864×480 960×720 1024×576 1280×720 1600×896 1920×1080. In Raw/yuyv422 mode two additional sizes are available. 2304×1296 2304×1536.

I pointed my webcam at the building out my window, giving myself a rough grid pattern to look at and ran it through all of the h.264 sizes, and manually counted the horizontal and vertical blocks visible. 

I expected 640×480 and 640×360 to be the same horizontal FOV but have different vertical FOV. What actually happened in the FOV was that they displayed the same vertical FOV but different horizontal FOV.

I ran through all of the h264 resolutions, and the vertical FOV appeared to shrink slightly when I requested resolutions below 200, but otherwise stayed the same. 

Selecting 2304×1536 produced a slightly larger vertical FOV with the same horizontal FOV as 1920×1080. 2304×1296 seemed to produce the same FOV in both directions as 1920×1080.  Both of these resolutions run at lower frame rates and only in raw mode. I was testing them using ffmpeg transcoding and sending to my windows desktop with the command: ffmpeg -re -f v4l2 -video_size 2304×1536 -framerate 2 -input_format yuyv422 -i /dev/video0 -f mpegts udp://192.168.0.10:8090

The C920 advertises a Diagonal FOV of 78°, but I didn’t find official meaning of that.  I found a nice bit of information at http://therandomlab.blogspot.com/2013/03/logitech-c920-and-c910-fields-of-view.html that describes it as explicitly as being when the camera is running in 16×9 mode. 

I will probably get around to writing a program to more accurately produce the results.  Here’s my manual table:

Resolution Width Height Blocks Floors Width/Height Ratio MegaPixels
160×90  160 90 9 8 1.777778 0.01
160×120  160 120 7 8 1.333333 0.01
176×144  176 144 7 9 1.222222 0.02
320×180  320 180 9 8 1.777778 0.05
320×240  320 240 7 9 1.333333 0.07
352×288  352 288 7 9 1.222222 0.1
432×240  432 240 10 9 1.8 0.1
640×360  640 360 10 9 1.777778 0.23
640×480  640 480 7 9 1.333333 0.3
800×448  800 448 10 9 1.785714 0.35
800×600  800 600 7 9 1.333333 0.48
864×480  864 480 10 9 1.8 0.41
960×720  960 720 7 9 1.333333 0.69
1024×576  1024 576 10 9 1.777778 0.58
1280×720  1280 720 10 9 1.777778 0.92
1600×896  1600 896 10 9 1.785714 1.43
1920×1080 1920 1080 10 9 1.777778 2.07
2304×1296 2304 1296     1.777778 2.98
2304×1536 2304 1536     1.5 3.53
  16 9     1.777778
  4 3     1.333333

 

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