Missing IR filter in camera and TOF sensor

I recently discovered, that one of the back camera modules seems not to have an IR filter built in. But since the TOF sensor also uses an IR signal for the distance measurement this can cause pink spots in the image if you take a picture from things with a reflective surface:

You can also spot this, when you look into a mirror with the camera. You can clearly see the “pink” light coming out of the TOF sensor. Yes, often this is not an issue, since you usually don’t take pictures of reflective surfaces with the camera pointing exactly at a 90 degree angle to it - but still this is an annoying behaviour.

Did anyone else also experienced this? I already contacted the support about this but have to wait for an answer.

Maybe this could be fixed in the software - just turn off the TOF sensor right before taking the image. Since this also happens with Open Camera, the fix would need to be applied in the internal camera libraries.

4 Likes

None of the cameras seem to have IR cut filters (including front cam). Tested with a TV remote pointed directly into the cameras.

That is weird. Usually, color cameras come with IR cut filters and mono cameras come without them.

1 Like

Indeed, there is no IR filter in any of the camera modules, just verified this with a remote control as well.

I also compared this with other phones like Xiaomi Mi 9 Lite and iPhone SE. The Xiaomi Mi 9 Lite also does not have an IR filter, but the iPhone SE has.

So it seems not uncommon to have no IR filter - but nevertheless this is a bad decision when a TOF sensor with infrared signals is used for autofocus assistance.

2 Likes

the TOF sensors IR wavelengths (probably 905 nm or 1000 nm) can be recognized by the camera sensor, as we can easily test like described above. now filtering these wavelengths via the transparent camera cover isn’t easy. you need special (some expensive like gold, but you only need to add homeopathic amounts) colorants, which only absorb IR but not in the visible range. otherwise they would eat visible red light or also other wavelengths.
I guess the more reasonable way would be to do a wavelength cut via the camera software. why this is being done for an iphone but not for the FP4, I don’t know.

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.