[Elphel-support] 答复: 答复: 答复: 答复: sync stereo with lidar

Tue Mar 6 21:57:40 PST 2018

Hello Winston,

You may set compression quality to 100% and there will be no quantization, compression itself will be lossless (in regular JPEG most of the image degradation is related to de-mosaic). There will still be gamma conversion that introduces loss, but it is less than the sensor natural shot noise as it is explained in the article I gave you a link to. Image acquisition is a noisy  process - if you acquire twice the same scene they will never be bit-to-bit equal, so there is not much sense to preserve each noise value. You only need lossless compression when editing images, especially if you save/load them many times - even small errors would accumulate.

JP4 was developed for Google Books and later also used for Street View - it provides some compression while keeping RMS error under under 1 output count, so there will be no measurable improvement in 3d reconstruction.

I would recommend to use compression quality 97-98% (as we do) - it provides very good quality and still compresses 5MPix images to ~2MB in size. You may compare 100% and 98% quality images yourself.

Andrey

---- On Tue, 06 Mar 2018 21:33:39 -0800 Tao Zhang<tao.zhang at blacksesame.com.cn> wrote ---- 

    Hi Andrey,
 I think the JP4 image is lossy compressed. The block is cause by that. Is there a way to get lossless images?
 Thanks.

  Tao Zhang
 章   涛

   发件人: Winston Zhang 
 发送时间: 2018年3月7日 13:12
 收件人: Andrey Filippov <andrey at elphel.com>
 抄送: Elphel Support <support-list at support.elphel.com>; Elphel Sales | Olga Filippova <sales at elphel.com>; Tao Zhang <tao.zhang at blacksesame.com.cn>; Qun Gu <qun.gu at blacksesame.com>; Pioneer Li <pioneer.li at blacksesame.com.cn>
 主题: 答复: [Elphel-support] 答复: 答复: 答复: sync stereo with lidar

 Hi, Andrey
       Please take a look at attachments. The rawJP4 image was captured from the camera, and I converted it and got the result as result.png. But when I magnified this image, I found some block included 16x16 grid. I did not know the reason. Can you explain it.(The grid image please take look at grid.png).
       Another question is that the result image is single channel but not three channel like as rgb-channel. But if I converted it through the jp4viewer, the result is color image. Why? How do you do this?

 Best Regrad!
 Yicheng-Zhang
 Email:  winston.zhang at blacksesame.com.cn
 Teil:    18516291005
 Addr:   707 room, 7th floor, building 4th, No.1761, Zhangdong road, Pudong area

   发件人: Andrey Filippov [mailto:andrey at elphel.com] 
 发送时间: 2018年3月6日 星期二 15:58
 收件人: Winston Zhang <winston.zhang at blacksesame.com.cn>
 抄送: Elphel Support <support-list at support.elphel.com>; Elphel Sales | Olga Filippova <sales at elphel.com>; Tao Zhang <tao.zhang at blacksesame.com.cn>; Qun Gu <qun.gu at blacksesame.com>; Pioneer Li <pioneer.li at blacksesame.com.cn>
 主题: Re: [Elphel-support] 答复: 答复: 答复: sync stereo with lidar

  Winston,

 There are several ways how to set the JP4 mode:

 1) set it from the camera GUI (click Camera Control Interface port #), then click camera icon (top left), then "More details" and select color mode to jp4.
 2) set with "Parameter Editor": follow Parameter Editor from the home page, check bit 2 - "Image color, quality ..." -> "View/Edit Current", set "COLOR: line New value to 5 (it is jp4) and click "Apply" button.
 3) make this mode default(after either 1) or 2) )- save current settings in "Parameter Editor" (previous page) - Press topmost "Save" button (you may later change comments for the settings). Then you may set saved settings as default (select it and then press "Update default"). Next time you start the camera it will use these settings.
 Then repeat the same for the other channel.

 Andrey

 ---- On Mon, 05 Mar 2018 01:46:22 -0800 Winston Zhang<winston.zhang at blacksesame.com.cn> wrote ---- 

    Hello, Andrey,
              I need information inside camera. How can I get jp4 format image? What is the image default format? If I try the command line “wget http://192.168.0.9:2323/img -O filename.jp4”, Can I get the jp4 format Image?             Thank you! 
 ”

  Best Regrad!
  Yicheng-Zhang
  Email:  winston.zhang at blacksesame.com.cn
  Teil:    18516291005
  Addr:   707 room, 7th floor, building 4th, No.1761, Zhangdong road, Pudong area

   发件人: Andrey Filippov [mailto:andrey at elphel.com] 
 发送时间: 2018年3月2日 星期五 10:47
 收件人: Winston Zhang <winston.zhang at blacksesame.com.cn>; Elphel Support <support-list at support.elphel.com>
 抄送: Tao Zhang <tao.zhang at blacksesame.com.cn>; Elphel Support <support-list at support.elphel.com>; Elphel Sales | Olga Filippova <sales at elphel.com>; Qun Gu <qun.gu at blacksesame.com>; Pioneer Li <pioneer.li at blacksesame.com.cn>
 主题: Re: 答复: 答复: [Elphel-support] sync stereo with lidar

  Hello Winston,

 Do you need information inside camera or for post-processing on a host PC?

 Sensor has 12 bits, and using JP4 format (https://wiki.elphel.com/wiki/JP4) you can restore image data with the error less than the pixel shot noise

 Here is an article explaining why it is so:

  http://linuxdevices.io/how-many-bits-are-really-needed-in-the-image-pixels/

  With ImageJ plugin you can convert JP4 file to 32-bit TIFF

  Andrey

  ---- On Thu, 01 Mar 2018 17:17:14 -0800 Winston Zhang<winston.zhang at blacksesame.com.cn> wrote ---- 

    Hello,
       Does this camera image pixel have 10 bit of the single channel? And how can I get it? Thank you.

  Best Regrad!
  Yicheng-Zhang
  Email:  winston.zhang at blacksesame.com.cn
  Teil:    18516291005
  Addr:   707 room, 7th floor, building 4th, No.1761, Zhangdong road, Pudong area

   发件人: Andrey Filippov [mailto:andrey at elphel.com] 
 发送时间: 2018年2月1日 星期四 13:49
 收件人: Tao Zhang <tao.zhang at blacksesame.com.cn>
 抄送: Elphel Support <support-list at support.elphel.com>; Elphel Sales | Olga Filippova <sales at elphel.com>; Winston Zhang <winston.zhang at blacksesame.com.cn>; Qun Gu <qun.gu at blacksesame.com>; Pioneer Li <pioneer.li at blacksesame.com.cn>
 主题: Re: 答复: [Elphel-support] sync stereo with lidar

  Tao,

 USB GPS does not have 1pps signal (only serial has), precise synchronization is not possible that way. GPS time is available in each frame Exif header data - recorded on internal SSD or sent over the network.

 The high resolution time stamps (1 microsecond step) are also provided with each  image, but they use internal camera clock, not the GPS.

 This is why for precise synchronization you need to use event logger- it records events and timestamps them using the same clock.

 If you had serial GPS with  https://wiki.elphel.com/wiki/103696 - you would still need to use event logger - with serial GPS there will be 1 PPS precise GPS events timestamped with camera internal clock, and the images timestamped wit the same clock - that provides absolute calibration for the camera internal clock.

 Without serial GPS you may use pulses from the LIDAR (it is possible to provide LIDAR pulse number over the Ethernet in addition to the precise time over the sync cable)

 Andrey

 ---- On Wed, 31 Jan 2018 18:12:00 -0800 Tao Zhang<tao.zhang at blacksesame.com.cn> wrote ---- 

    Hi Andrey,
 We prefer to use GPS to synchronize stereo with lidar.
 Where do those images that contain timestamp store in internal disk? Can we get it from ethernet continuously?

   Tao Zhang
  章   涛

   发件人: Andrey Filippov [mailto:andrey at elphel.com] 
 发送时间: 2018年2月1日 1:52
 收件人: Tao Zhang <tao.zhang at blacksesame.com.cn>
 抄送: Elphel Support <support-list at support.elphel.com>; Elphel Sales | Olga Filippova <sales at elphel.com>; Winston Zhang <winston.zhang at blacksesame.com.cn>; Qun Gu <qun.gu at blacksesame.com>; Pioneer Li <pioneer.li at blacksesame.com.cn>
 主题: Re: [Elphel-support] sync stereo with lidar

  Hi Tao,

 There are several ways how to do that:
 One method would be be to get camera sync pulses for each frame and use external electronics to match with the LIDAR.
 Another is to provide pulses from the LIDAR to the camera and record them with in-camera FPGA logger (https://wiki.elphel.com/wiki/Event_logger), together with the camera frames. In this case the camera will record 2 types of events:
  -  image frames with the frame number, frame timestamp that will be recorded in each frame header as Exif.
  - external pulse
 Each of the two types of events will have a logger timestamp (with microsecond resolution). Logger can also record GPS timestamps (for serial GPS only and 103696 board -https://wiki.elphel.com/wiki/103696) and IMU (https://wiki.elphel.com/wiki/103695), in your case there are just 2 types listed above.

 Both output (+5V pulses) and input (3.3V..5.0V) are available through the 2.5mm audio connector (marked "sync"  https://wiki.elphel.com/images/0/0f/NC393-CS_marked_ports.jpeg ), here is the pinout and description: https://wiki.elphel.com/wiki/103891 .

 Andrey

 ---- On Wed, 31 Jan 2018 04:19:04 -0800 Tao Zhang<tao.zhang at blacksesame.com.cn> wrote ---- 

    Hi Andrey,
 We are going to use stereo with lidar. We need to sync stereo frames with lidar point cloud. Do you have any suggestions on how to do that?
 Thanks.

   Tao Zhang
  章   涛

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