「Raspberry PI」啟用Webcam拍照

Raspberry 如果要啟用webcam拍照，除了用OpenCV之外，

還有一個簡單方法，安裝fswebcam這個套件。

 sudo apt-get install fswebcam  

安裝過程大致上長這樣

 pi@boywhy-pi2:~ $ sudo apt-get install fswebcam  
 Reading package lists... Done  
 Building dependency tree      
 Reading state information... Done  
 The following packages were automatically installed and are no longer required:  
  pypy-upstream-doc wiringpi  
 Use 'apt-get autoremove' to remove them.  
 The following NEW packages will be installed:  
  fswebcam  
 0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.  
 Need to get 44.0 kB of archives.  
 After this operation, 105 kB of additional disk space will be used.  
 Get:1 http://mirrordirector.raspbian.org/raspbian/ jessie/main fswebcam armhf 20140113-1 [44.0 kB]  
 Fetched 44.0 kB in 1s (35.9 kB/s)    
 Selecting previously unselected package fswebcam.  
 (Reading database ... 126790 files and directories currently installed.)  
 Preparing to unpack .../fswebcam_20140113-1_armhf.deb ...  
 Unpacking fswebcam (20140113-1) ...  
 Processing triggers for man-db (2.7.0.2-5) ...  
 Setting up fswebcam (20140113-1) ...  
 pi@boywhy-pi2:~ $   

拍一張，存成test.jpg (採用預設的解析度，大概是320*240 左右）

 fswebcam test.jpg  

指定拍照解析度（如果Webcam不支援的話，fswebcam會自動調整成最接近的解析度）

 fswebcam -r 1280x720 image2.jpg  

訊息大致上長這個樣子，注意 Adjusting resolution from 1024x720 to 640x480. 代表相機不支援1024x720，被強制改成640x480了

 pi@boywhy-pi2:~ $ fswebcam -p YUYV -r 1024x720 test.jpg  
 --- Opening /dev/video0...  
 Trying source module v4l2...  
 /dev/video0 opened.  
 No input was specified, using the first.  
 Adjusting resolution from 1024x720 to 640x480.  
 --- Capturing frame...  
 Captured frame in 0.00 seconds.  
 --- Processing captured image...  
 Writing JPEG image to 'test.jpg'.  
 pi@boywhy-pi2:~ $   

以上拍照後，相片上都會有個banner寫著拍照時間等等，如果不要的話，可以加上

--no-banner這個參數，相片就不會有多餘的資訊被打上去。

 fswebcam -r 1280x720 --no-banner image3.jpg  

如果拍照出來是黑黑的一片，注意一下是否有發生如下的訊息

GD Error: gd-jpeg: JPEG library reports unrecoverable error: Not a JPEG file: 

俺試了2支Webcam，羅技C310 是OK的，但是C 170 就會出現這個錯誤訊息。

俺查詢了相關資料後，做了一個嘗試，改變 palette format 為YUYV後正常，

推測應該是Webcam硬體支援上的問題。

 pi@boywhy-pi2:~ $ fswebcam -p YUYV test.jpg  
 --- Opening /dev/video0...  
 Trying source module v4l2...  
 /dev/video0 opened.  
 No input was specified, using the first.  
 Adjusting resolution from 384x288 to 352x288.  
 --- Capturing frame...  
 Captured frame in 0.00 seconds.  
 --- Processing captured image...  
 Writing JPEG image to 'test.jpg'.  
 pi@boywhy-pi2:~ $   

正常取得照片

參考資料：

USING A STANDARD USB WEBCAM

fswebcam - gd-jpeg: JPEG library reports unrecoverable error