树莓派摄像头检测高亮LED颜色

一直想用摄像头拍摄来检查LED的颜色。但一直存在以下几个问题：

LDE太亮，拍出来LDE中心的颜色基本上都是白色的。很多时候要加滤光片，而合适的滤光片不好找，这就增加了难度和成本。
摄像头拍照的参数无法修改。比如曝光补偿EV，感光度ISO，快门时间shutter speed, 这几个参数直接影响了成像的颜色和亮度。
摄像头像数，成像效果，速度，成本。一般的USB摄像头便宜，但是成像效果不好，无法很好地还原颜色，速度也偏慢。传统的工业摄像头成像效果可以，速度也快，但是价格不菲，无法不心痛地大量使用。

难道没有解决方法吗？有的！经过对比多种摄像头，包括无牌子的USB网络摄像头，有名的罗技带自动对焦的USB网络摄像头，某宝9.9的便宜手动对焦摄像头，还有带显微镜功能的USB摄像头都达不到想要的效果。终于双11，淘了几款树莓派的摄影像头，发现带手动对焦功能的一款500W像数，可以达到效果，而且也不到100RMB, 比较惊喜的是加上红外补光灯还可以夜间拍摄！这不是官方的那款，而是兼容的。

先来看看效果，一般拍摄的效果，这种情况只能判断出亮还是灭，无法判断颜色：

调节参数(感光度，快门时间)之后：

局部细节如下，这种图片就很好判断啦！

上面第一张图片使用的命令如下，明显LED的地方已经过曝光发白了。

raspistill -t 10000 -v -q 100 -roi 0,0,1,1 -o roi2.jpg

1	raspistill -t 10000 -v -q 100 -roi 0,0,1,1 -o roi2.jpg

第二张图片使用的命令如下，这里主要是把快门时间ss调成100微妙，感光度ISO调成200，LED的封装体正确地显示出颜色来，发光的点还是很明亮显白色，但这不影响我们判断颜色了，我们可以选择封装体的地方来判断，这样就可以让摄像头直接对着LED拍照检查颜色了。

raspistill -t 10000 -v -q 100 -roi 0,0,1,1 -ss 100 -ISO 200 -o roi.jpg

1	raspistill -t 10000 -v -q 100 -roi 0,0,1,1 -ss 100 -ISO 200 -o roi.jpg

这里使用的摄像头如下，这是一款CSI接口的摄像头，兼用树莓派的接口，所以要用在树莓派上了。使用命令raspistill, raspipid可以方便地获取到图片。在raspi-config里启用摄像头后，重启树莓派就可以用这两个命令了。

还有v2.1的一款800W像数的，有空再试试效果。

来个合照和raspistill的帮助信息：

pi@raspberrypi:~ $ raspistill
raspistill Camera App v1.3.8

Runs camera for specific time, and take JPG capture at end if requested

usage: raspistill [options]

Image parameter commands

-?, --help      : This help information
-w, --width     : Set image width <size>
-h, --height    : Set image height <size>
-q, --quality   : Set jpeg quality <0 to 100>
-r, --raw       : Add raw bayer data to jpeg metadata
-o, --output    : Output filename <filename> (to write to stdout, use '-o -'). I                                                                                        f not specified, no file is saved
-l, --latest    : Link latest complete image to filename <filename>
-v, --verbose   : Output verbose information during run
-t, --timeout   : Time (in ms) before takes picture and shuts down (if not speci                                                                                        fied, set to 5s)
-th, --thumb    : Set thumbnail parameters (x:y:quality) or none
-d, --demo      : Run a demo mode (cycle through range of camera options, no cap                                                                                        ture)
-e, --encoding  : Encoding to use for output file (jpg, bmp, gif, png)
-x, --exif      : EXIF tag to apply to captures (format as 'key=value') or none
-tl, --timelapse        : Timelapse mode. Takes a picture every <t>ms. %d == fra                                                                                        me number (Try: -o img_%04d.jpg)
-fp, --fullpreview      : Run the preview using the still capture resolution (ma                                                                                        y reduce preview fps)
-k, --keypress  : Wait between captures for a ENTER, X then ENTER to exit
-s, --signal    : Wait between captures for a SIGUSR1 from another process
-g, --gl        : Draw preview to texture instead of using video render componen                                                                                        t
-gc, --glcapture        : Capture the GL frame-buffer instead of the camera imag                                                                                        e
-set, --settings        : Retrieve camera settings and write to stdout
-cs, --camselect        : Select camera <number>. Default 0
-bm, --burst    : Enable 'burst capture mode'
-md, --mode     : Force sensor mode. 0=auto. See docs for other modes available
-dt, --datetime : Replace output pattern (%d) with DateTime (MonthDayHourMinSec)
-ts, --timestamp        : Replace output pattern (%d) with unix timestamp (secon                                                                                        ds since 1970)
-fs, --framestart       : Starting frame number in output pattern(%d)
-rs, --restart  : JPEG Restart interval (default of 0 for none)

Preview parameter commands

-p, --preview   : Preview window settings <'x,y,w,h'>
-f, --fullscreen        : Fullscreen preview mode
-op, --opacity  : Preview window opacity (0-255)
-n, --nopreview : Do not display a preview window

Image parameter commands

-sh, --sharpness        : Set image sharpness (-100 to 100)
-co, --contrast : Set image contrast (-100 to 100)
-br, --brightness       : Set image brightness (0 to 100)
-sa, --saturation       : Set image saturation (-100 to 100)
-ISO, --ISO     : Set capture ISO
-vs, --vstab    : Turn on video stabilisation
-ev, --ev       : Set EV compensation - steps of 1/6 stop
-ex, --exposure : Set exposure mode (see Notes)
-awb, --awb     : Set AWB mode (see Notes)
-ifx, --imxfx   : Set image effect (see Notes)
-cfx, --colfx   : Set colour effect (U:V)
-mm, --metering : Set metering mode (see Notes)
-rot, --rotation        : Set image rotation (0-359)
-hf, --hflip    : Set horizontal flip
-vf, --vflip    : Set vertical flip
-roi, --roi     : Set region of interest (x,y,w,d as normalised coordinates [0.0                                                                                        -1.0])
-ss, --shutter  : Set shutter speed in microseconds
-awbg, --awbgains       : Set AWB gains - AWB mode must be off
-drc, --drc     : Set DRC Level (see Notes)
-st, --stats    : Force recomputation of statistics on stills capture pass
-a, --annotate  : Enable/Set annotate flags or text
-3d, --stereo   : Select stereoscopic mode
-dec, --decimate        : Half width/height of stereo image
-3dswap, --3dswap       : Swap camera order for stereoscopic
-ae, --annotateex       : Set extra annotation parameters (text size, text colou                                                                                        r(hex YUV), bg colour(hex YUV))


Notes

Exposure mode options :
off,auto,night,nightpreview,backlight,spotlight,sports,snow,beach,verylong,fixed                                                                                        fps,antishake,fireworks

AWB mode options :
off,auto,sun,cloud,shade,tungsten,fluorescent,incandescent,flash,horizon

Image Effect mode options :
none,negative,solarise,sketch,denoise,emboss,oilpaint,hatch,gpen,pastel,watercol                                                                                        our,film,blur,saturation,colourswap,washedout,posterise,colourpoint,colourbalanc                                                                                        e,cartoon

Metering Mode options :
average,spot,backlit,matrix

Dynamic Range Compression (DRC) options :
off,low,med,high

Preview parameter commands

-gs, --glscene  : GL scene square,teapot,mirror,yuv,sobel
-gw, --glwin    : GL window settings <'x,y,w,h'>

pi@raspberrypi:~ $ raspistill

raspistill Camera App v1.3.8

Runs camera for specific time, and take JPG capture at end if requested

usage: raspistill [options]

Image parameter commands

-?, --help : This help information

-w, --width : Set image width <size>

-h, --height : Set image height <size>

-q, --quality : Set jpeg quality <0 to 100>

-r, --raw : Add raw bayer data to jpeg metadata

-o, --output : Output filename <filename> (to write to stdout, use '-o -'). I f not specified, no file is saved

-l, --latest : Link latest complete image to filename <filename>

-v, --verbose : Output verbose information during run

-t, --timeout : Time (in ms) before takes picture and shuts down (if not speci fied, set to 5s)

-th, --thumb : Set thumbnail parameters (x:y:quality) or none

-d, --demo : Run a demo mode (cycle through range of camera options, no cap ture)

-e, --encoding : Encoding to use for output file (jpg, bmp, gif, png)

-x, --exif : EXIF tag to apply to captures (format as 'key=value') or none

-tl, --timelapse : Timelapse mode. Takes a picture every <t>ms. %d == fra me number (Try: -o img_%04d.jpg)

-fp, --fullpreview : Run the preview using the still capture resolution (ma y reduce preview fps)

-k, --keypress : Wait between captures for a ENTER, X then ENTER to exit

-s, --signal : Wait between captures for a SIGUSR1 from another process

-g, --gl : Draw preview to texture instead of using video render componen t

-gc, --glcapture : Capture the GL frame-buffer instead of the camera imag e

-set, --settings : Retrieve camera settings and write to stdout

-cs, --camselect : Select camera <number>. Default 0

-bm, --burst : Enable 'burst capture mode'

-md, --mode : Force sensor mode. 0=auto. See docs for other modes available

-dt, --datetime : Replace output pattern (%d) with DateTime (MonthDayHourMinSec)

-ts, --timestamp : Replace output pattern (%d) with unix timestamp (secon ds since 1970)

-fs, --framestart : Starting frame number in output pattern(%d)

-rs, --restart : JPEG Restart interval (default of 0 for none)

Preview parameter commands

-p, --preview : Preview window settings <'x,y,w,h'>

-f, --fullscreen : Fullscreen preview mode

-op, --opacity : Preview window opacity (0-255)

-n, --nopreview : Do not display a preview window

Image parameter commands

-sh, --sharpness : Set image sharpness (-100 to 100)

-co, --contrast : Set image contrast (-100 to 100)

-br, --brightness : Set image brightness (0 to 100)

-sa, --saturation : Set image saturation (-100 to 100)

-ISO, --ISO : Set capture ISO

-vs, --vstab : Turn on video stabilisation

-ev, --ev : Set EV compensation - steps of 1/6 stop

-ex, --exposure : Set exposure mode (see Notes)

-awb, --awb : Set AWB mode (see Notes)

-ifx, --imxfx : Set image effect (see Notes)

-cfx, --colfx : Set colour effect (U:V)

-mm, --metering : Set metering mode (see Notes)

-rot, --rotation : Set image rotation (0-359)

-hf, --hflip : Set horizontal flip

-vf, --vflip : Set vertical flip

-roi, --roi : Set region of interest (x,y,w,d as normalised coordinates [0.0 -1.0])

-ss, --shutter : Set shutter speed in microseconds

-awbg, --awbgains : Set AWB gains - AWB mode must be off

-drc, --drc : Set DRC Level (see Notes)

-st, --stats : Force recomputation of statistics on stills capture pass

-a, --annotate : Enable/Set annotate flags or text

-3d, --stereo : Select stereoscopic mode

-dec, --decimate : Half width/height of stereo image

-3dswap, --3dswap : Swap camera order for stereoscopic

-ae, --annotateex : Set extra annotation parameters (text size, text colou r(hex YUV), bg colour(hex YUV))

Notes

Exposure mode options :

off,auto,night,nightpreview,backlight,spotlight,sports,snow,beach,verylong,fixed fps,antishake,fireworks

AWB mode options :

off,auto,sun,cloud,shade,tungsten,fluorescent,incandescent,flash,horizon

Image Effect mode options :

none,negative,solarise,sketch,denoise,emboss,oilpaint,hatch,gpen,pastel,watercol our,film,blur,saturation,colourswap,washedout,posterise,colourpoint,colourbalanc e,cartoon

Metering Mode options :

average,spot,backlit,matrix

Dynamic Range Compression (DRC) options :

off,low,med,high

Preview parameter commands

-gs, --glscene : GL scene square,teapot,mirror,yuv,sobel

-gw, --glwin : GL window settings <'x,y,w,h'>

很多时候想用python来做这个拍摄工作，然后可以结合其它的功能，有2个方法，一是在python里调用raspistill. 二是用picamera模块。以下是用picamera模块做的小程序，获取到一张图片。

from picamera import PiCamera
from io import BytesIO
from PIL import Image

camera = PiCamera(resolution=(1280,720), framerate=30)
# Set ISO to the desired value
camera.iso = 200
# Now fix the values
camera.exposure_mode = 'off'
camera.shutter_speed = 100

# Finally, take several photos with the fixed settings
#camera.capture_sequence(['009image%02d.jpg' % i for i in range(10)])
#camera.capture('009image_led.jpg')

stream = BytesIO()
camera.capture(stream, format='jpeg')
stream.seek(0)
image=Image.open(stream)
image.save("009image_led_using_stream_to_PIL.jpg")

from picamera import PiCamera

from io import BytesIO

from PIL import Image

camera = PiCamera(resolution=(1280,720), framerate=30)

# Set ISO to the desired value

camera.iso = 200

# Now fix the values

camera.exposure_mode = 'off'

camera.shutter_speed = 100

# Finally, take several photos with the fixed settings

#camera.capture_sequence(['009image%02d.jpg' % i for i in range(10)])

#camera.capture('009image_led.jpg')

stream = BytesIO()

camera.capture(stream, format='jpeg')

stream.seek(0)

image=Image.open(stream)

image.save("009image_led_using_stream_to_PIL.jpg")

程序里通过BytesIO()流，把图片转成了PIL的image, 然后再用image的save()方法保存成图片，这样就可以应用PIL对图片在内存里进行相应的计算，有时候不是必须存为文件的时候，这样做就可以减少IO操作，毕竟树莓派的写操作还是比较慢的，而且如果反复写SD卡的寿命估计也不长。

其实也可以用注悉掉的那两行其中一行都可以直接把图像保存起来，不是必须转成流再转成PIL的image再保存的。

同样获取到一张理想的图片：

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