Bayer output for OV7725

OpenMV Products
#1

Hi Guys
Whats the difference between the Bayer RAW and Bayer processed RAW on the OV7725 sensor? For getting a 640x480 image, you guys mentioned in a previous discussion that because the SRAM is too small to store the RGB, you use the Bayer RAW output from the sensor and then de-bayer it.
So have a bunch of questions here

  1. So do you work with Bayer RAW or processed Bayer RAW?
  2. Is de-bayer the same as demosiac’ing?
  3. How many FPS would be possible if we did this is the F7 processor, if the final goal is to store a jpeg image in the SD card?
  4. What c file do you guys have your de-bayer code in?

I would appreciate any feedback :slight_smile:

#2
  1. So do you work with Bayer RAW or processed Bayer RAW?

Processed Bayer

  1. Is de-bayer the same as demosiac’ing?

Yes Demosaicing - Wikipedia

  1. How many FPS would be possible if we did this is the F7 processor, if the final goal is to store a jpeg image in the SD card?

Debayer, compress and write to SD VGA frames will be slow, definitely less than 10FPS

  1. What c file do you guys have your de-bayer code in?

omv/img/imlib.c

#3

Thank a ton for the quick reply! :slight_smile:

#4

Hi Ibrahim
Quick follow up question. Do you have a link for the algorithm you use for the conversion of Bayer to RGB/YUV image? Im trying to learn the theory of the conversion and then work with the code. Right now the code is a bit overwhelming for me.
-Thanks

#5

Yeah: https://github.com/openmv/openmv/blob/master/src/omv/img/imlib.h#L309

#6

wow! holy cow! thanks for the lightning fast reply!!!

#7

have a follow up question here. When we de-mosiac a 640x480 bayer image (size of 307KB) to RGB565 or RGB888 or YUV, its size would increase to more than 512KB (size of SRAM). So I feel it does not seem to be possible to do this de-mosiacing within the F7 itself. Am I wrong here.
How do you guys do it? Or do you just transfer the raw image over USB to the computer and perform the processing in your openMV software?

#8

We turn it into a jpg image while doing the operation. So, the full image never is stored in RAM.

#9

hmmm… so you guys are going from raw bayer to jpg directly? When you de-mosiac, you are adding the all three RGB values to each pixel. So 24bit/pixel

So are you just converting each 8x8 macro blocks to jpeg before moving on to the next macro block? Am I in the right direction here?

#10

Yup, that’s exactly what we are doing.