QHYCCD QHY8L - Manual (Page 13)

13
Chapter 3
Set the GAIN and OFFSET
GAIN is the pre-ADC (analog-to-digital converter) programmable gain
amplifier setting. OFFSET is the ADC voltage offset setting. The correct
setting of OFFSET and GAIN can change the CCD's system gain, to make the
CCD output signal range match the ADC quantization range, so as to get the
best dynamic range.
Suitable for most GAIN and OFFSET Settings:
1. Set the gain=0, set the exposure time to 0, cover the lens, then shoot a BIAS frame.
2. Watch the local average value of the captured images (you can use the Noise
Analyze function of EZCAP, image process->noise analyze). The ideal average value is
around 500 to 1000. If the value is higher, then you should reduce the OFFSET. If the
value is lower, then you should increase the OFFSET. Repeat steps 1-2 to obtain the
ideal OFFSET value.
3. Open the lens cover, increase the exposure time, then use a uniform light source to
take a saturated exposure image. Watch the local average value of the captured
images. If the value is less than 60000, you should increase the value of GAIN. If the
value is 65535, you should reduce the value of GAIN. Repeat this step to obtain the
appropriate GAIN value.
4. Under this GAIN value, repeat steps 1-2 to obtain more accurate OFFSET value.
Note: For some QHYCCD products when you use bin modes of 2*2, 3*3, 4*4, images
may reach 65535 even the gain is 0, so you just set the gain to 0.