Fixed compressed image format for image_transport compatibility

[iory]

Fixes

Description of the changes:

• The current compressed image format is jpeg. compressed image published by image_transport's format is bgra8; jpeg compressed bgr8. This PR modified the format to be compatible with image_transport.

Before submitting a Pull Request:

• [x] I reviewed CONTRIBUTING.md
• [x] I built my changes locally
• [x] I tested my changes with a device

I tested changes on:

• [ ] Windows
• [x] Linux

The result of this PR as follows.

$ rostopic echo /k4a/rgb/image_raw/compressed --noarr -n1
header:
  seq: 22
  stamp:
    secs: 1595593360
    nsecs: 195937704
  frame_id: "rgb_camera_link"
format: "bgra8; jpeg compressed bgr8"
data: "<array type: uint8, length: 615359>"
---

[ooeygui]

Hi @iory, Thank you for your contribution. Can you tell me how this manifested as a problem?

[iory]

I am taking data with rosbag and analyzing images and save those as the compressed images for data reduction. This PR's change is necessary because I am reading the value of format to detect if the image contained in the rosbag is compressed. Following code is a sample of format parsing function.

def compressed_format(msg):
    fmt, compr_type = msg.format.split(';')
    # remove white space
    fmt = fmt.strip()
    return fmt, compr_type

[ooeygui]

Sorry for the delay on this.

[iory]

Thank you!