[libcamera-devel] IMX258 and speckled images

[Dave Stevenson]

Hi All.

A quick query as I'm aware that others on here are using the Sony IMX258 sensor.
Are you using the sensor driver as-is from mainline[1], or does it need changes?

A third party manufacturer has made an IMX258 module for the Pi[2],
but we're getting dark speckles in the raw image, which we're guessing
is down to PDAF pixel correction. The module manufacturer also
believes that there may be versions of the module with and without
PDAF pixels, which may well explain the issue.

It seems that register 0x4e21 being set to 0x14 by the driver is the
main cause, and the default of 0x10 gives good images. Of course
register 0x4e21 isn't documented in any of the datasheets and appnotes
I have from Sony. I have an enquiry in with them, but I wondered if
others had seen similar issues, or might have documentation about that
register.

Thanks
  Dave

[1] https://github.com/torvalds/linux/blob/master/drivers/media/i2c/imx258.c
[2] https://soho-enterprise.com/products/