MT9M114 - Violet Colour at Higher Framesizes

My OpenMV Cam H7 R2 using the MT9M114 image sensor is only able to capture a dark violet image when using a frame size above QVGA. The same image sensor on an OpenMV Came Plus does not have the same issues. I suspect it has something to do with the reduced RAM on the H7 board, but I haven’t been able to find a way to get around it.

Has anyone here experienced this issue and found a solution?


After some digging in the documentation, I saw the following:


RAW BAYER image pixel format. If you try to make the frame size too big to fit in the frame buffer your OpenMV Cam will set the pixel format to BAYER so that you can capture images but no image processing methods will be operational.

Does this mean that the frame buffer on the standard H7 board only can support RGB565 with a resolution up to QVGA 320x240? Are there any tricks for allocating more memory to the frame buffer to support higher resolutions or can I only get higher resolutions on this board if I use an image sensor with JPEG compression such as the OV5640?

Hi, the current version of the H7 R2 firmware doesn’t handle debayering in all modes. This is fixes in the latest unreleased firmware. However, we cannot handle above QVGA with color on the H7 non-plus as the image doesn’t fit in RAM.

When the image doesn’t fit in RAM we automatically switch to a bayer image which is 2x smaller than an RGB565 image. Previously we didn’t handle bayer that well. But, we have been upgrading the firmware where more functions handle it.

Anyway, once the new firmware comes out you should be able to have a proper bayer image with any cropping. Also, quite a few find_x() methods work on bayer now also. However, there’s still going to be RAM issues on the H7 normal.

Yes, in general stay at 320x240 or below on the H7 regular.

Thanks a lot for the response. Compiling the latest code from github improved the Bayer images a lot, but the images are still quite dark and not as nice as the equivalent bayer images from the OV5640 sensor. Is this due to differences in the image sensor, or do you believe that firmware adjustments can make them equivalent?

No, bayer images don’t look good because there’s no ISP processing. It’s the raw image from the sensor. The feature is there primarily for folks who want raw unprocessed images.