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一只有理想的羊驼

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在使用ZED Camera时，我希望获得原始的照片（未经过校正，对齐处理）。但由于系统是Ubuntu 14.04，只有ZED SDK 1.1.0版本支持，而对应的zed-ros-wrapper v1.0.0只能订阅已经经过校正对齐的照片/camera/left/image_rect_color和/camera/rgb/image_rect_color（不过zed-ros-wrapper v1.2.0版本开始就开始提供原始照片的订阅，Topic为/camera/left/image_raw_color和/camera/right/image_raw_color）。

如果直接使用ZED SDK所提供的图片获取接口'grab(); retrieveImage()'，按照说明也是已经经过了对齐操作了，并非是原始照片。

还好由于ZED Camera是标准的网络摄像头，使用v4l2-ctl --all指令，有以下显示：

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Driver Info (not using libv4l2):
	Driver name   : uvcvideo
	Card type     : ZED
	Bus info      : usb-0000:00:14.0-3
	Driver version: 4.4.59
	Capabilities  : 0x84200001
		Video Capture
		Streaming
		Device Capabilities
	Device Caps   : 0x04200001
		Video Capture
		Streaming
Priority: 2
Video input : 0 (Camera 1: ok)
Format Video Capture:
	Width/Height  : 2560/720
	Pixel Format  : 'YUYV'
	Field         : None
	Bytes per Line: 5120
	Size Image    : 3686400
	Colorspace    : SRGB
	Custom Info   : feedcafe
Crop Capability Video Capture:
	Bounds      : Left 0, Top 0, Width 2560, Height 720
	Default     : Left 0, Top 0, Width 2560, Height 720
	Pixel Aspect: 1/1
Selection: crop_default, Left 0, Top 0, Width 2560, Height 720
Selection: crop_bounds, Left 0, Top 0, Width 2560, Height 720
Streaming Parameters Video Capture:
	Capabilities     : timeperframe
	Frames per second: 30.000 (30/1)
	Read buffers     : 0
                     brightness (int)    : min=0 max=8 step=1 default=4 value=4
                       contrast (int)    : min=0 max=8 step=1 default=4 value=4
                     saturation (int)    : min=0 max=8 step=1 default=4 value=4
                            hue (int)    : min=0 max=11 step=1 default=0 value=0
 white_balance_temperature_auto (bool)   : default=1 value=1
                           gain (int)    : min=0 max=8 step=1 default=4 value=4
           power_line_frequency (menu)   : min=0 max=2 default=1 value=1
      white_balance_temperature (int)    : min=2800 max=6500 step=100 default=4600 value=4600 flags=inactive
                      sharpness (int)    : min=0 max=8 step=1 default=4 value=4
                  exposure_auto (menu)   : min=0 max=3 default=0 value=2
              exposure_absolute (int)    : min=5000 max=80000 step=5000 default=60000 value=45000 flags=inactive
         exposure_auto_priority (bool)   : default=0 value=0

所以可以使用OpenCV（opencv-2.4.13.2版本）自带的VideoCapture函数获取原始照片：

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cv::VideoCapture* camera_ = new cv::VideoCapture(0);
cv::Mat raw, left_image, right_image;
if (camera_->grab()) {
	camera_->retrieve(raw);
	cv::Rect left_rect(0, 0, width_ / 2, height_);
	cv::Rect right_rect(width_ / 2, 0, width_ / 2, height_);
	left_image = raw(left_rect);
	right_image = raw(right_rect);
	cv::waitKey(10);
	return true;
}

但在读取，设置摄像头快门速度（EXPOSURE）时，

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camera_->set(CV_CAP_PROP_EXPOSURE, exposure_);
exposure_ = camera_->get(CV_CAP_PROP_EXPOSURE);

出现了以下错误：

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HIGHGUI ERROR: V4L2: Unable to get property Exposure(9963793) - Invalid argument
HIGHGUI ERROR: V4L: Exposure control in V4L is not supported

发现是OpenCV的bug1，并且在最新的3.*版本已经修复，对于opencv-2.4.13.2版本需要手动修复。

解决方法

>在opencv-2.4.13.2/modules/highgui/src/cap_v4l.cpp文件中，将V4L2_CID_EXPOSURE替换为V4L2_CID_EXPOSURE_ABSOLUTE，重新build一次。

重新运行程序，发现读取问题解决了，但是设置参数时依然出现问题：

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HIGHGUI ERROR: V4L2: Failed to set control "10094850": Input/output error (value 12500)
HIGHGUI WARNING: Setting property 10094850 through v4l2 failed. Trying with v4l1.
HIGHGUI ERROR: V4L: Exposure control in V4L is not supported

后来终于找到解决方法，需要先通过设置'exposure_auto'，关闭自动模式，才能进行快门设置2。终端中运行：

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v4l2-ctl --set-ctrl=exposure_auto=2

很奇怪，exposure_auto貌似只能设置为0/2。

为了让exposure_absolute生效，还需设置：

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v4l2-ctl --set-ctrl=exposure_auto_priority=1

现在可以在C++中通过OpenCV设置摄像头的快门了。

以上方法经过测试发现都是无效的，V4L2无法对快门速度进行设置。

后来，发现可以通过对zed-ros-wrapper进行修改，进行快门设置。

在zed_wrapper_nodelet.cpp中添加控制exposure的代码：

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int main(int argc, char **argv) {

// Defines the exposure control. A -1 value enable the AutoExposure/AutoGain control.
// Affected value should be between 0 and 100 for manual control. 
// A 0 value only disable automode without modifing the last auto values, 
// while a 1 to 100 value disable auto mode and set exposure to chosen value
int exposure = 50;

nh_ns.getParam("exposure", exposure);

// before zed->grab()
zed->setCameraSettingsValue(sl::zed::ZED_EXPOSURE, exposure);
}

然后就可以在launch文件中添加控制快门语句：

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<param name="exposure" value="50"/>

  1. https://github.com/opencv/opencv/pull/6393↩︎

  2. https://askubuntu.com/questions/211971/v4l2-ctl-exposure-auto-setting-fails↩︎

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Dependencies1

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# CMake
sudo apt-get install cmake

# google-glog + gflags
sudo apt-get install libgoogle-glog-dev

# BLAS & LAPACK
sudo apt-get install libatlas-base-dev

# Eigen3
sudo apt-get install libeigen3-dev

# SuiteSparse and CXSparse (optional)
# - If you want to build Ceres as a *static* library (the default)
#   you can use the SuiteSparse package in the main Ubuntu package
#   repository:
sudo apt-get install libsuitesparse-dev

# - However, if you want to build Ceres as a *shared* library, you must
#   add the following PPA:
sudo add-apt-repository ppa:bzindovic/suitesparse-bugfix-1319687
sudo apt-get update
sudo apt-get install libsuitesparse-dev
Install2
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git clone https://ceres-solver.googlesource.com/ceres-solver
cd ceres-solver
mkdir ceres-bin
cd ceres-bin
cmake ..
make -j3
make test
# Optionally install Ceres, it can also be exported using CMake which
# allows Ceres to be used without requiring installation, see the documentation
# for the EXPORT_BUILD_DIR option for more information.
sudo make install

Test

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bin/simple_bundle_adjuster ../data/problem-16-22106-pre.txt
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iter      cost      cost_change  |gradient|   |step|    tr_ratio  tr_radius  ls_iter  iter_time  total_time
   0  4.185660e+06    0.00e+00    1.09e+08   0.00e+00   0.00e+00  1.00e+04        0    8.67e-02    2.07e-01
   1  1.062590e+05    4.08e+06    8.99e+06   5.36e+02   9.82e-01  3.00e+04        1    1.85e-01    3.93e-01
   2  4.992817e+04    5.63e+04    8.32e+06   3.19e+02   6.52e-01  3.09e+04        1    1.72e-01    5.65e-01
   3  1.899774e+04    3.09e+04    1.60e+06   1.24e+02   9.77e-01  9.26e+04        1    1.77e-01    7.42e-01
   4  1.808729e+04    9.10e+02    3.97e+05   6.39e+01   9.51e-01  2.78e+05        1    1.69e-01    9.11e-01
   5  1.803399e+04    5.33e+01    1.48e+04   1.23e+01   9.99e-01  8.33e+05        1    1.74e-01    1.09e+00
   6  1.803390e+04    9.02e-02    6.35e+01   8.00e-01   1.00e+00  2.50e+06        1    1.75e-01    1.26e+00

Solver Summary (v 1.13.0-eigen-(3.3.4)-lapack-suitesparse-(4.2.1)-cxsparse-(3.1.2)-openmp)

                                     Original                  Reduced
Parameter blocks                        22122                    22122
Parameters                              66462                    66462
Residual blocks                         83718                    83718
Residual                               167436                   167436

Minimizer                        TRUST_REGION

Dense linear algebra library            EIGEN
Trust region strategy     LEVENBERG_MARQUARDT

                                        Given                     Used
Linear solver                     DENSE_SCHUR              DENSE_SCHUR
Threads                                     1                        1
Linear solver threads                       1                        1
Linear solver ordering              AUTOMATIC                 22106,16
Schur structure                         2,3,9                    2,3,9

Cost:
Initial                          4.185660e+06
Final                            1.803390e+04
Change                           4.167626e+06

Minimizer iterations                        7
Successful steps                            7
Unsuccessful steps                          0

Time (in seconds):
Preprocessor                           0.1207

  Residual evaluation                  0.1168
  Jacobian evaluation                  0.5111
  Linear solver                        0.5164
Minimizer                              1.2377

Postprocessor                          0.0032
Total                                  1.3617

Termination:                      CONVERGENCE (Function tolerance reached. |cost_change|/cost: 1.769761e-09 <= 1.000000e-06)

  1. http://ceres-solver.org/installation.html↩︎

  2. http://ceres-solver.org/installation.html↩︎

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