I'm recently exploring the possibility to change lens of the rapsberry camera v2 and/or remove the lens completely for some contact imaging. I removed the lens and lens holder of camera v2 completely with the help of a razor blade (would love to share details if anyone is interested).
However, after testing the lens-removed sensor response by illuminating with a plane wave (uniform illumination), the sensor response doesn't look quite uniform. The raw image shows some slowly varying response (a non-uniformity of ~30%), as can be seen in the red (R), green (G1) and blue (B) channels of this raw image below. (The raw image data is extracted from the large jpeg either using the "dcraw" or the documented python code. Thanks to those dedicated engineers and pioneering hackers!!!)
(For instance, the green (G1) channel seems to be brighter in the middle instead of a uniform shade.) I'm wondering if anyone has seem similar non-uniformity problem of camera v2.
According to the Sony IMX219PQ document http://www.sony.net/Products/SC-HP/new_ ... 219_e.html,
So this shading might be due to:The IMX219PQ has a lens shading correction function with four independent colors. It can be used for not only normal lens shading correction, and also can serve as an individual module adjustment of deviation in the lens assembly process during the module fabrication.
(1) The sensor fabrication defects.
(2) Shading correction for the lens, which is removed in my case.
Either of these seems to be related to some shade correction. Does anyone know if this correction is a "pre-processing" by adjusting the gain of each pixels (before digitized), or if this is a "post-processing" on the raw image (after digitized). (I've tried previously similar lens-removal for camera v1, OV5647 and it had uniform response. Not sure why this Sony IMX219 has such a non-uniformity in the raw image. )
Also from the Sony IMX219PQ document page,
Is there a way to get or modify this built-in OTP, in order to beat or get around this auto- shade correction?Calibration data is written in a built-in OTP during the module inspection to contribute to the short loading time when the camera is turned on. One from three tables can be selected according to color temperature and there exists two-table blending mode for interpolation.