Can not set awb_gains

[messismore]

Hi everyone,

I am trying to hard code a certain white balance for a time lapse camera, however, it seems like setting camera.awb_gains = Fraction(497, 256), Fraction(177, 128) has no effect. The code below outputs a different awb_gains each time.

import picamera
import time
from fractions import Fraction


camera = picamera.PiCamera()
camera.framerate = 10

time.sleep(1)
# This capture discovers initial AWB and SS.
camera.capture('try.jpg')
camera.shutter_speed = camera.exposure_speed
currentss = camera.exposure_speed
camera.exposure_mode = 'off'
camera.resolution = (1920, 1080)
camera.awb_mode = 'off'
camera.awb_gains = (Fraction(497, 256), Fraction(177, 128))

print camera.awb_gains

$ python wb_gains_test.py 
(Fraction(203, 256), Fraction(675, 256))
$ python wb_gains_test.py 
(Fraction(211, 256), Fraction(367, 128))
$ python wb_gains_test.py
(Fraction(197, 256), Fraction(675, 256))

What a I doing wrong?

[Berryfier]

The value of awb_gains used by print seems to take a while to settle. Inserting repeat print and capture statements will reveal this unexpected behaviour. However, looking at repeat captures, the used value of awb_gains does seem to be very close to what is input.

[6by9]

Reading awb_gains returns the values used on the last completed image.

You've set new values and immediately requested the settings before a new frame has been generated, therefore you're reading back stale data. Either set awb_gains before you start the camera streaming, or delay by at least one frame time, and you should get the value you set (rounded to the nearest 1/256th).

[waveform80]

This looks pretty comprehensively answered to me, so I'll close it (feel free to re-open if you've got anything further to add though!)

[JolleJolles]

I have a similar issue. I created the following script based on the picamera documentation

`from time import sleep
from picamera import PiCamera
from fractions import Fraction

camera = PiCamera(resolution=(1280, 720), framerate=30)
camera.iso = 100
sleep(2)
camera.shutter_speed = camera.exposure_speed
camera.exposure_mode = 'off'
g = camera.awb_gains
camera.awb_mode = 'off'
camera.awb_gains = (2.5, 2.5)
camera.capture('try.jpg')
print(camera.awb_gains)`

But whatever I put as camera.awb_gains, also with Fractions, the values returned are always very similar fractions in the range (Fraction(167, 128), Fraction(257, 128)). The images returned also always have a nice white balance and not the overly red or blue that I would expect with the provided awb_gains.