MT9M114 auto-gain / exposure

OpenMV Products
#1

Hello, I have the MT9M114 sensor on the H7 R2. I’ve fixed auto_gain to false and turned off auto exposure. Exposure and gain read back correctly as fixed. But I’m still noticing when I look at a grayscale histogram that there appears to still quite a bit of gain adjustment happening, because the grayscale distribution gradually shifts for a second or two after a sudden change in brightness in the scene - well after the scene has stopped changing. And the statistics.mean() drifts for a while after the scene change is complete.

I read elsewhere in this forum that the MT9M114 is more of a SoC and is more complicated, with some methods are not implemented for it. Does it offer a fully manual control? Is there additional gain control happening in the sensor that OpenMV is not able to control?

I also ran the ‘sensor manual gain control.py’ example script as-is, to make sure I didn’t make an error, and it also clearly shows change in gain despite the script locking the gain.

Firmware 4.3.1.

#2

Hi, you should be able to set the exposure and gain control. We cannot control color balance settings however. The MT9M114 doesn’t really offer us the same level of control we normally have.

If you want the datasheet and register reference I can provide that. However, low level color balance support is… extremely complex.

#3

Thanks. The sensor’s readback of gain and exposure does appear to get fixed, but even so the image clearly reacts to a change in lighting and adjusts brightness. Could the sensor’s color balance adjustments cause that on a grayscale image?

If the MT9M114 is challenging to control, does the MT9V034 sensor offer better/easier ‘full-manual’ control to get a true fix? I think I have one we deployed on one of the units in our facility.

#4

Yeah, the MT9V034 is full manual control. It’s much better.

And yes, the MT9M114 might be doing some color balancing to adjust the image.