Date: Wed, 15 Dec 1999 18:43:40 GMT From: Henry Bruce Subject: More CPiA developer notes To: jtotland@eunet.no Cc: Henry.BRUCE Jarl, A number of people have contacted me with questions on the more subtle aspects of anti-flicker operation. There have also been some questions on reading ApCor settings and the compression quality metric. Here is some information that may help the more advanced developers. I don't have time to include it in the developers guide, so I'd appreciate it if you could put this in the appropriate place on your web site. Anti-Flicker ------------ The developer's guide document gives no indication of what value to enter in the AllowableOverExposure parameter so I've attached some code which calculates a suitable value for the AllowableOverExposure parameter (see overexp.c). This value should be calculated and written each time the brightness is changed. As described in the document, SetExposure must be used immediately after enabling flicker control to ensure that the flicker control works with suitable exposure values. The calculations detailed in section 3.12.2 should be implemented and Exposure values written after each change of Coarse Jump, i.e. after initialisation and when the lighting frequency changes from 60Hz to 50Hz or vice versa. Note that new exposure values are *not* required after each change of the OverExposure parameter. Section 3.12.3 should be implemented but sections 3.12.5 may be ignored if Flicker Control is not going to be switched on and off by the user. Compression "Quality" --------------------- Quality is defined as the compression ratio for a given frame. e.g. compression ratio of 1:1 is quality 1 (the highest) while compression ratio of 5:1 would be quality 5. It's not a perfect measure of quality but it is one that is readily available from the camera without computational overhead. ApCor ----- Just to confirm, there is no way to read the ApCor value, you should kee p a shadow copy.