Public Lab Research note


Overexposure using YUV format and manual exposure settings with Infragram webcam

by jarrarte | August 06, 2014 14:35 | 258 views | 1 comments | #11018 | 258 views | 1 comments | #11018 06 Aug 14:35

Read more: publiclab.org/n/11018


jarrarte was awarded the Empiricism Barnstar by warren for their work in this research note.


What I want to do

I want to use the Infragram webcam (link) in bright sunny environments, so I need to effectively control exposure.

It seems there are some issues when using manual exposure combined with YUV format. This issue is not present with MPEG format.

My attempt and results

I'm trying to use YUV format for capturing raw images. The automatic exposure settings are too bright for the tests I'm doing. However, when I change its settings to manual exposure and a minimum exposure value (value=8) the captured image is way brighter than with automatic exposure. The gamma and gain settings are also at their minimum (100 and 32, respectively).

However, there are clear differences between capturing a MPEG stream and a YUV stream. MPEG has a much better quality, YUV over exposes some parts of the image. Here are some test captures using v4l2-ctl:

MPEG with auto exposure

MPEG-auto.jpg

MPEG with manual exposure (value = 8)

MPEG-manual8.jpg

YUV with auto exposure

YUV-auto.jpg

YUV with manual exposure (value = 8)

YUV-manual8.jpg

v4l2-ctl settings

All images shared these settings:

settings.jpg

Questions and next steps

  • Does this also happen to other Infragram webcam owners?
  • Is there other particular settings I should be considering?

Why I'm interested

I'm interested in using this webcam in bright sunny environments, so I need to effectively control exposure. MPEG may have compression artifacts that I want to avoid, so I'm interested in capturing YUV raw frames.

Additional info:

Google groups discussion - link

My notebook: jarrarte@jarrarte-nb:~ > inxi -F System: Host: jarrarte-nb Kernel: 3.13.0-32-generic x86_64 (64 bit) Desktop: KDE 4.13.2 Distro: Linux Mint 17 Qiana Machine: System: LENOVO (portable) product: 4291S3D version: ThinkPad X220 Mobo: LENOVO model: 4291S3D Bios: LENOVO version: 8DET69WW (1.39 ) date: 07/18/2013 CPU: Dual core Intel Core i5-2540M CPU (-HT-MCP-) cache: 3072 KB flags: (lm nx sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx) Clock Speeds: 1: 800.00 MHz 2: 800.00 MHz 3: 800.00 MHz 4: 800.00 MHz Graphics: Card: Intel 2nd Generation Core Processor Family Integrated Graphics Controller X.Org: 1.15.1 drivers: intel (unloaded: fbdev,vesa) Resolution: 1366x768@60.0hz GLX Renderer: Mesa DRI Intel Sandybridge Mobile GLX Version: 3.0 Mesa 10.1.3 Audio: Card-1: Intel 6 Series/C200 Series Chipset Family High Definition Audio Controller driver: snd_hda_intel Card-2: Z-Star Micro driver: USB Audio Sound: Advanced Linux Sound Architecture ver: k3.13.0-32-generic Network: Card-1: Intel 82579LM Gigabit Network Connection driver: e1000e IF: eth0 state: down mac: f0🇩🇪f1:fc:30:bc Card-2: Intel Centrino Advanced-N 6205 [Taylor Peak] driver: iwlwifi IF: wlan0 state: up mac: 8c:70:5a:8d:5d:7c Drives: HDD Total Size: 256.1GB (74.9% used) 1: id: /dev/sda model: SAMSUNG_SSD_830 size: 256.1GB Partition: ID: / size: 19G used: 16G (89%) fs: ext4 ID: /boot size: 457M used: 82M (19%) fs: ext2 RAID: No RAID devices detected - /proc/mdstat and md_mod kernel raid module present Sensors: System Temperatures: cpu: 49.0C mobo: N/A Fan Speeds (in rpm): cpu: 1961 Info: Processes: 240 Uptime: 20:16 Memory: 3086.9/7867.8MB Client: Shell inxi: 1.8.4

lsusb output when plugging the webcam: [20256.036523] usb 2-1.2: USB disconnect, device number 6 [20264.678411] usb 2-1.2: new high-speed USB device number 7 using ehci-pci [20264.812963] usb 2-1.2: New USB device found, idVendor=0ac8, idProduct=3470 [20264.812967] usb 2-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=0 [20264.812969] usb 2-1.2: Product: USB2.0 Camera [20264.812971] usb 2-1.2: Manufacturer: Vimicro Corp. [20264.813760] uvcvideo: Found UVC 1.00 device USB2.0 Camera (0ac8:3470) [20264.815820] input: USB2.0 Camera as /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.2/2-1.2:1.0/input/input20

v4l2-ctl output: jarrarte@jarrarte-nb:~ > sudo v4l2-ctl -d 1 --all Driver Info (not using libv4l2): Driver name : uvcvideo Card type : USB2.0 Camera Bus info : usb-0000:00:1d.0-1.2 Driver version: 3.13.11 Capabilities : 0x84000001 Video Capture Streaming Device Capabilities Device Caps : 0x04000001 Video Capture Streaming Priority: 2 Video input : 0 (Camera 1: ok) Format Video Capture: Width/Height : 1280/720 Pixel Format : 'MJPG' Field : None Bytes per Line: 0 Size Image : 1843200 Colorspace : Unknown (00000000) Crop Capability Video Capture: Bounds : Left 0, Top 0, Width 1280, Height 720 Default : Left 0, Top 0, Width 1280, Height 720 Pixel Aspect: 1/1 Streaming Parameters Video Capture: Capabilities : timeperframe Frames per second: 30.000 (30/1) Read buffers : 0 brightness (int) : min=-10 max=10 step=1 default=-28672 value=-10 contrast (int) : min=0 max=20 step=1 default=36873 value=20 saturation (int) : min=0 max=10 step=1 default=6 value=6 hue (int) : min=-5 max=5 step=1 default=-28672 value=-5 white_balance_temperature_auto (bool) : default=1 value=1 gamma (int) : min=100 max=200 step=1 default=41110 value=100 gain (int) : min=32 max=48 step=1 default=45088 value=32 power_line_frequency (menu) : min=0 max=2 default=1 value=1 white_balance_temperature (int) : min=2800 max=6500 step=1 default=47460 value=2800 flags=inactive sharpness (int) : min=0 max=10 step=1 default=36868 value=10 backlight_compensation (int) : min=0 max=1 step=1 default=45056 value=1 exposure_auto (menu) : min=0 max=3 default=3 value=3 exposure_absolute (int) : min=8 max=16384 step=1 default=512 value=8 flags=inactive


1 Comments

Thank you so much for posting this!!!!! Very helpful even just on the basis of showing how to change image capture mode. I haven't tried these tests but am eager to hear from other Infragrammers.

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