How to get depth value from saved .png img?

[fwf-lernen]

Required Info
Camera Model	D455
Firmware Version	05.12.11.00
Operating System & Version	Ubuntu 16.04
Kernel Version (Linux Only)	4.15.0
Platform	PC
SDK Version	2.42.0
Language	C

Issue Description

Like #5546 (comment) ,I have saved depth image by
cv::Mat matDepth(cv::Size(imgWidth,imgHeight) , CV_16UC1 , (void *)depth.get_data() , cv::Mat::AUTO_STEP)
However I have no idea how to get actual distance from saved imgs through cv::imread.
In rs_sensor.h,
RS2_FORMAT_Z16 , /**< 16-bit linear depth values. **The depth is meters is equal to depth scale * pixel value**. */
So, is that means I just need to use cv::imread and multiply a depth scale factor? If so, how can I get the scale factor?

[MartyG-RealSense]

Hi @fwf-lernen The C++ script in the link below, as part of a discussion on retrieving depth values from a PNG image with imread, may be useful to you:

#2200 (comment)

An alternative approach to the problem is described in this link:

https://stackoverflow.com/questions/51728827/using-a-depth-map/51759748#51759748

However, when RealSense depth data is saved as a PNG, most of the depth information is lost. It is therefore better if possible to save the data as a .raw format image file that preserves the depth detail. The link below provides scripting for retrieving depth information from a .raw file.

#2231 (comment)

Instead of obtaining the depth information from a PNG image, there is also the option of converting the cv::mat back into a RealSense rs2::frame, as described in the link below.

#2634

[fwf-lernen]

@MartyG-RealSense Thank you very much! That's really helpful.

[MartyG-RealSense]

You are very welcome @fwf-lernen - thanks for the update!