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46 lines
2.2 KiB
Python
46 lines
2.2 KiB
Python
# Sensor Auto Gain Control
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#
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# This example shows off how to control the sensor's gain
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# using the automatic gain control algorithm.
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# What's the difference between gain and exposure control?
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#
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# Well, by increasing the exposure time for the image you're getting more
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# light on the camera. This gives you the best signal to noise ratio. You
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# in general always want to increase the expsoure time... except, when you
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# increase the exposure time you decrease the maximum possible frame rate
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# and if anything moves in the image it will start to blur more with a
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# higher exposure time. Gain control allows you to increase the output per
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# pixel using analog and digital multipliers... however, it also amplifies
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# noise. So, it's best to let the exposure increase as much as possible
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# and then use gain control to make up any remaining ground.
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# We can achieve the above by setting a gain ceiling on the automatic
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# gain control algorithm. Once this is set the algorithm will have to
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# increase the exposure time to meet any gain needs versus using gain
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# to do so. However, this comes at the price of the exposure time varying
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# more when the lighting changes versus the exposure being constant and
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# the gain changing.
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import sensor, image, time
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sensor.reset() # Reset and initialize the sensor.
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sensor.set_pixformat(sensor.RGB565) # Set pixel format to RGB565 (or GRAYSCALE)
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sensor.set_framesize(sensor.QVGA) # Set frame size to QVGA (320x240)
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# The gain db ceiling maxes out at about 24 db for the OV7725 sensor.
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sensor.set_auto_gain(True, gain_db_ceiling = 16.0) # Default gain.
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# Note! If you set the gain ceiling to low without adjusting the exposure control
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# target value then you'll just get a lot of oscillation from the exposure
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# control if it's on.
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sensor.skip_frames(time = 2000) # Wait for settings take effect.
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clock = time.clock() # Create a clock object to track the FPS.
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while(True):
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clock.tick() # Update the FPS clock.
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img = sensor.snapshot() # Take a picture and return the image.
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print("FPS %f, Gain %f dB, Exposure %d us" % \
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(clock.fps(), sensor.get_gain_db(), sensor.get_exposure_us()))
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