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changing_exposures.md

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Manually changing the exposure time on a running camera

This article explains the facilities provided by royale-ros to manually change the exposure times on the fly for a running camera. Changing the exposure is set on a per stream basis.

The first step is to inspect our current camera configuration.

$ rosrun royale_ros dump
{
  "Device": {
    "Id": "0005-4804-0050-1916",
    "Name": "PICOFLEXX"
  },
  "Imager": {
    "CurrentUseCase": {
      "ExposureLimits": {
        "57082": [
          "27",
          "2000"
        ]
      },
      "ExposureMode": {
        "57082": "0"
      },
      "FrameRate": "5",
      "MaxFrameRate": "5",
      "Name": "MODE_9_5FPS_2000",
      "NumberOfStreams": "1",
      "Streams": [
        "57082"
      ]
    },
    "MaxSensorHeight": "171",
    "MaxSensorWidth": "224",
    "UseCases": [
      "MODE_9_5FPS_2000",
      "MODE_9_10FPS_1000",
      "MODE_9_15FPS_700",
      "MODE_9_25FPS_450",
      "MODE_5_35FPS_600",
      "MODE_5_45FPS_500",
      "MODE_MIXED_30_5",
      "MODE_MIXED_50_5"
    ]
  }
}

The first thing to note is that the imager is configured to use a single stream 57082. Next, we see that this particular stream is set to a manual ExposureMode:

"ExposureMode": {
    "57082": "0"
 },

NOTE: manual exposure = 0, auto exposure = 1.

We also note the exposure limits for this stream:

"ExposureLimits": {
    "57082": [
      "27",
      "2000"
    ]
},

The units of the exposure limits are in microseconds. Let's now see what the camera is reporting for the actual exposure times used:

$ rostopic echo /camera/stream/1/exposure_times
header:
  seq: 1536
  stamp:
    secs: 1503082272
    nsecs: 754138947
  frame_id: camera_optical_link
usec: [200, 2000, 2000]
---
^C

Lets now set the long exposure to 1000 usecs. This is done by publishing on the SetExposureTime topic:

$ rostopic pub -1 /camera/SetExposureTime royale_ros/SetExposureTime "streamid: 57082
exposure_usecs: 1000"
publishing and latching message for 3.0 seconds

Now, let's see what the camera is reporting:

$ rostopic echo /camera/stream/1/exposure_times
header:
  seq: 2480
  stamp:
    secs: 1503082461
    nsecs: 649880886
  frame_id: camera_optical_link
usec: [200, 1000, 1000]
---
^C

If your camera_nodelet is running with level 2 access, you will have access to finer-grained control over all of the exposure times via the /camera/SetExposureTimes service:

$ rostopic pub -1 /camera/SetExposureTimes royale_ros/SetExposureTimes "streamid: 0
exposure_usecs: [100, 1000, 1750]"

And,

$ rostopic echo /camera/stream/1/exposure_times
header:
  seq: 5528
  stamp:
    secs: 1526690890
    nsecs: 376950026
  frame_id: "camera_optical_link"
usec: [100, 1000, 1750]
---
^C

To be clear, the output from the Dump service will report the exposure limits for the configured use case. The stream/X/exposure_times topic will publish the actual exposure times used for image acquisition.