ROS Resources: Documentation | Support | Discussion Forum | Index | Service Status | ros @ Robotics Stack Exchange

Attention: Answers.ros.org is deprecated as of August the 11th, 2023. Please visit robotics.stackexchange.com to ask a new question. This site will remain online in read-only mode during the transition and into the foreseeable future. Selected questions and answers have been migrated, and redirects have been put in place to direct users to the corresponding questions on Robotics Stack Exchange. Additional details are available here.

0

Decode compressedDepth message from compressed_depth_image_transport

asked 2016-11-07 17:08:44 -0500

gariepya
43 ●3 ●6 ●10

Hi,

I am using the compressed_depth_image_transport to compress a Kinect depth image before letting it go through rosbridge (the client won't have ROS or opencv installed, only pip-installed libs). The image is float32 compressed in png.

On the client, I receive the image encoded in base64 by rosbridge. After decoding the base64 string, what I have is bytes that are supposed to be the compressed image. However, I cannot figure out the format of the image. For instance, if I wrtite directly the bytes to a ".png" file, I cannot open it using an image viewer. I also get exceptions if I try to load the bytes using Pillow, pypng, scipy, etc.

How does compressed_depth_image_transport works? I have seen in the source code that it uses cv::imencode, does it produce a valid png file content as I expect?

Thank you!

edit retag flag offensive close merge delete

1 Answer

Sort by » oldest newest most voted

3

answered 2016-11-07 19:15:34 -0500

gariepya
43 ●3 ●6 ●10

I managed to make it work.

According to this source file the encoder puts a header at the beginning of the file. According to libpng, the first bytes of any png are 89 50 4e 47 0d 0a 1a 0a. By inspection, I found that the first 12 bytes are the header of compressed_depth_image_transport and the rest is a valid png file.

edit flag offensive delete link

Comments

Nice one. Thanks for reporting back.

gvdhoorn ( 2016-11-08 02:09:41 -0500 )edit

Thank you so much gariepya! Removing these first 12 bytes is the solution to the problem with which I honestly wasted days of precious working time.

Martin Bischoff ( 2017-02-15 05:36:32 -0500 )edit

Question Tools

1 follower

Stats

Asked: 2016-11-07 17:08:44 -0500

Seen: 780 times

Last updated: Nov 07 '16

Related questions

ROS Answers is licensed under Creative Commons Attribution 3.0 Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.

Powered by Askbot version 0.10.2