Composite Shots

Composite shots.

Several shots ot the same scene can be overlayed in your favorite photo program. This can result in reduced noise, and maybe even increased resolution.  This might be good for "product" shots.

Noise reduction example: The CP950 shows some noise in shadow areas. While this is typical of all of the "1/2 inch" 2 Mpixel CCD cameras, and the 950 is pretty good as far as those cameras go, there is still some improvment to be had. This problem appears to be even worse in the new crop of 1/2 inch 3 Mpixel cameras, perhaps due to the reduced size of each sensor element.


The shot above illustrates the noise. This is an enlarged area from a CP50 shot about 240 pixels square. Note the noise on the woodwork to the upper left. This shot was 1/100 at f3.0, ISO 100, so the lighting was  not particularly dark.


Above, an enlarged crop from a composite shot showing reduced noise. To produce this shot, four identical shots were taken. These shots were composited in PhotoPaint 9. Examine the wood and the reflection in the glass again, you can see that a lot of the random noise has averaged out, without much/any loss of detail. Another  commonly used technique to reduce noise is to apply a blur filter, sometimes to just the Green  or blue channel, but that invariably looses detail. This technique preserves detail while averaging out random noise.

To take shots like these, just take several shots of the subject. Obviously, you can't use this technique if you or the subject is moving.  A tripod is best but is not essential, you can line the shots up by eye later.

To composite the shots in PhotoPaint (I'm sure that the Photoshop technique is similar).

* Load both shots.

* Resample to 2X normal size.

* Use the picker tool to pick a shot. Then Edit Copy the entire shot.

* Select the other shot, then Edit Paste. Pick paste as new object.

* Move the second shot around on the screen. Right click on the shot that you are pasting and pick properties. Pick Normal merge, 50% opacity.  I also experimented with 33% opacity, which was also effective.

* As you move the shots around, you will be able to see both. Align them as best as possible. If you didn't use a tripod you will have to rotate your shot to align it, which is difficult.

* When done, right click on the pasted shot, pick merge with background.

Repeat with another shot! The fixed shot above is a merger of four shots.  There does not appear to be much gain in going beyond three shots though.

Ideas: The actual reason that I did this was to try to synthesize a higher resolution by combining several slightly out of phase shots. This was done for some of the Mars Pathfinder photos. I may have succeded (did I?), but I am not sure that the result is any better than would have been obtained by simple interpolation. I am still working on this; no doubt the techniques used by NASA are a lot more complicated that what I can accomplish. I'll post any further developments.