Dither amount

Just wondering how the SGP dither amount is translated to an actual movement in PHD. I’ve been using the Medium dither setting in SGP with a 1.0x scaling factor in PHD and looking a the guide log this is resulting in a movement of up to +/- 1 (I assume pixel) in the lock position. The actual movements for each dither appear to vary quite randomly.

How much movement would I expect if I increase the SGP dither amount from Medium to High?


For the socket server (PHD1 implemenation) those are defined in PHD. It may be better to ask on the PHD forum. I want to say that they map to 1, 5, 10, 15 and 20 pixels but I can’t recall for sure.

Currently SGP only uses the socket server implementation of PHD. So we just tell PHD to dither and send in the “Amount” which is Small, Medium, High, Very High, Extreme. For SGP 2.4 using PHD2 we will have more control and we send in a specific pixel amount. The amounts we send map to the pixel values above, which should match the current PHD dither values.


So moving from Medium to High looks like it will double the dither amount (5 to 10 pixels) if I’m understanding that correctly.

Assuming that the values I have posted are correct…then yes. But I’m not 100% confident that those values are accurate. You’d have to ask the PHD folks to verify.



The dither amounts are:

+/- 0.5, 1.0, 2.0, 3.0, 5.0

The units are guide camera pixels, and PHD2 will multiply the value by the
dither scale factor (on the Global tab in the brain).


1 Like

Thanks Andy. Sounds like I need to increase this to High if I want the lock position to move more than a fraction of a pixel then.

Either that or increase the dither scale factor in PHD2. Either way would