Flipping the camera up-side-down

OpenMV Products
#1

Due to limited space inside my robot I decided to mount the OpenMV board inside it up-side-down. I figured it will not matter much, as I can simply just flip the y coordinate of whatever results of image processing I get, and it will amount to the same thing. However, I didn’t think about things like face detection, which will not work with up-side-down faces.

I’m now thinking about what I could do. I could flip the image after taking the snapshot and before processing it – it would take some more time, but could work. I looked at the Image class, but didn’t find a way to flip or rotate the image, though.

Next thought, I could probably configure the camera sensor to flip the image – some cameras do have such a function. But again, nothing like that in the Sensor class, except maybe for the raw access to the registers. So I started to look for the datasheet for the camera sensor, thinking that if such an option exists there, it would be explained. But the datasheet is not linked from https://openmv.io/docs/openmv/hardware/index.html and a quick Google search doesn’t seem to yield anything more than a few promotional pamphlets.

FInally, I could probably use a flipped cascade for the face detection, instead of the default one. However, looking at the XML files of the OpenCV examples, it doesn’t seem like it’s a trivial operation to do.

I guess I will simply figure out how to mount the camera right side up, unless someone has any more ideas or hints?

#2

We should be able to add vertical flip and horizontal mirror output to the sensor class. OmniVision sensors support this. The OV7725 does I know. For the OV2640 you can find the data sheet by googling for it here: http://www.uctronics.com/download/cam_module/OV2640DS.pdf

See Page 22. There’s a vertical flip and horizontal mirror register. So, use the register read and register write stuff for now. Its reg 04, bits 6 and 7.

#3

I’m going to implement those, for now you could use __write_reg/__read_reg to do the flipping:

sensor.__write_reg(0xFF, 0x01)
sensor.__write_reg(0x04, 0x28)

(Note: Those registers are for the OV2640)

#4

I found the datasheet for OV7725, I will look for the corresponding registers. Thanks!

#5

I guess I can’t read this datasheet, or I’m missing something obvious. The docs say:

Address: 0C, Name: COM3, Bit[3]: Vertical flip image ON/OFF selection

So I added this code just before the loop in the helloworld example:

sensor.__write_reg(0x0C, sensor.__read_reg(0x0C) | (1 << 7))

But it doesn’t seem to be doing anything…
Do I need to call something more to “commit” those values?

#6

This works on OV7725, you need to call it after all the sensor settings. I think you have an OV2640 though, or did you get one of the new cameras ?

#7

Ah, silly me, I thought OV7725 is the old one. Sorry, your code works perfectly, thank you!

#8

You’re welcome! I think we have a couple of extra OV7725 cams for development (freebies!), mail us at openmv@openmv.io if you want one.

#9

did the image rotation/ flip ever get implemented?

#10

See sensor.hmirror and sensor.vflip. Rotation has not been implemented yet though it would be easy to do.

#11

Hello kwagyeman! How to used the sensor.hmirror and sensor.vflip. Rotation function when by define the ROI field. I Need compared one image the diffenece between the up side down or left side right which by define the ROI fields.Thank you for your kindly support!

#12

sensor.set_vflip(True)
sensor.set_hmirror(True)

?

#13

Hello kwagyeman ,how to define the ROI used sensor.set_vflip or sensor.set_hmirror?

#14

Those commands flip the whole image. That’s what you want right?

#15

Hi,kwagyeman . I need only ROI field in one Image.Thanks!

#16

You can’t flip just an ROI. It’s the whole.image since that command is editing what’s generated from the camera.

#17

You could flip and then crop the output (set_windowing), it should have the same effect.

#18

Thank you iabdalkader, I will be try!