Dithering using software - Apologies if this is daft

[cuivenion]

Could the dithering effect not be implemented in software using crop instead of at the imaging stage? If you individually randomly cropped each sub by a few pixels that would have the same effect wouldn't it?

Obviously cropping all the subs individually would be a nightmare especially if you do cmos short exposure imaging, but I'm sure someone clever could automate it.

[Grant]

No - the stars would still be in the same relative position to the camera sensor as before so you wouldn't get the benefits of dithering which moves the images position on the sensor as it's captured.

[symmetal]

I'm afraid not. Dithering enables the image you're recording to be on different pixels on your camera between frames so that when stacked any different noise effects of individual pixels are averaged out. Cropping the image randomly would have no effect on which pixels your image has been recorded on so a section of your image will still be recorded on the same pixels with each frame.

Alan

Edit: Beaten to it. 

[cuivenion]

Ah well never mind.

[cuivenion]

But.. if you added an area of blacked in pixels that replaced the cropped area and did that with each sub so all the subs stayed the same resolution, the image would appear to move wouldn't it?

[Grant]

2 minutes ago, cuivenion said:

But.. if you added an area of blacked in pixels that replaced the cropped area and did that with each sub so all the subs stayed the same resolution, the image would appear to move wouldn't it?

It would appear to move in the image but, star X would still have fallen on the same collection of pixels on the camera sensor in the first place and that's what dithering is avoiding - it spreads the position of the captured image across different positions on the sensor to average out pixel to pixel differences.

[cuivenion]

Ah fair enough then.