Get RAW stream of webcam

We are using a camera that is detected correctly by the Image Acquisition Toolbox as Webcam. But the camera Firmware provides a wrong data format information. The Information it gives is YUY2 as format, but what it actually delivers is a 12bit per Pixel image (2 Bytes with 4 bit unused) in a BGGR Bayer pattern. Now when acquiring images with the Toolbox it misinterprets the image and outputs a 3-channel image. I assume it trys to convert my data from YUY2 to RGB which turns out to be wrong. Is there a way to get the raw byte stream from the webcam with the Toolbox?

[Rebecca Krosnick]

What is your desired output format?

What hardware and support packages are you using? What commands are you currently using to acquire the data?

Regarding the BGGR Bayer pattern, if you have the Image Processing Toolbox you may find the "demosaic" function helpful. It converts Bayer pattern encoded images to truecolor images: http://www.mathworks.com/help/images/ref/demosaic.html

[Michael Eschey]

The desired output format is uint16 with the original 12bit information.

The hardware is from leopard imaging LI-USB30-P031C.

We are already using the demosaicing function from Matlab with good results. The SDK of leopard imaging allows to store the raw stream which I can load from Matlab. So the demosaicing, gamma correction and our own color correction is applied. For a demonstrator that we want to build up we don't want to work with the offline data anymore, that is why we need the acquisition directly in Matlab. The whole interface of leopard imaging is a bit faulty though: They use that YUY2 meta information and acquire with direct show but redirect the stream before it is interpreted in any way. So probably they are not even aware it is wrong. Then they have simple bilinear demosaicing and a wrong color transform which creates bluish images. But at least I get the stream to make up for this myself. Former contact to leopard imaging regarding the hardware trigger was disappointing so I didn't ask for a correction in the firmware this time.

Our approach right now is to have a little direct show code snippet found on codeproject "Minimalistic direct show approach". This code works with the camera and provides the desired stream. Next step is to write an IMAQ adaptor ourselves with this code snippet.

[mario iobbi]

I have similar issue with another hardware from leopard (LI-USB30-M021XB) while using the direct show YUY2 format. Have you successfully made the IMAQ adapter with the direct show code snippet?

[Walter Roberson]

mario iobbi: please note that Michael Eschey will not have been notified about your question. Unfortunately I do not find a contact for Michael Eschey.

[Michael Eschey]

We did not write an IMAQ adapter after all and instead chose to compile it with MEX. The part to acquire the stream though would be the same. Nevertheless you would need to cope with gamma correction, demosaicing and color correction by yourself then.

[mario iobbi]

Thank you for responding. Glad to know that it is feasible but it is unfortunate that it isn't straightforward. You would not happen to still have the code and be willing to share the the code to aquire the stream someplace?

Answer 1

[Image Analyst]

What does this say:

fprintf('ReturnedColorspace = %s', vidobj.ReturnedColorspace);

where vidobj is your video object.

[Michael Eschey]

The returned colorspace is 'YCbCr'. Changing it to rgb doesn't change the output. Grayscale just gives me something monochrome which is not my image and only with 1Byte per pixel.

[Image Analyst]

How do you know that the gray scale output is not just raw bytes, which represent your mosaiced values? For example the Mandi "gray scale" demo image that ships with MATLAB?