Noisy Nights

The image on the left below illustrates the problem: At long exposures, the Fuji Super CCD generates apparently 'random' coloured speckles. The image on the right is the same image after following the technique illustrated here.

The Solution

I actually 'stole' the idea for removal of these speckles from the Sony DSC-F707.

A little bit of background. The speckles are actually caused by differing sensitivity of elements on the CCD, and are common to all digital cameras. Not a problem under normal usage, but crank up the shutter time and these 'hot pixels' shine through.

The way the Sony solves the problem is to take a black picture after a long exposure picture, and then 'subtract' the black picture from the long exposure picture. The theory is that the black picture will have the same noise and so can be removed from the long exposure picture to leave a noise free image.

Ah ha, I thought (and an apple fell on my head). I wonder if I can do the same with the 6900 and Photoshop. I'd previously noticed that all my pictures without digital zoom had speckles in the same place. (When you use digital zoom, they move - more on that later.)

So, I put the lens cap ON the camera and took a 3s black image at f2.8 - the same as settings as the picture I wanted to remove noise from.

An interesting lens cap, I'm sure you'll agree.

I then opened the 'lens cap' image in Photoshop and did 'Select All' followed by 'Copy'.

Then I opened the 'long exposure' image in Photoshop and did 'Paste'.

My 'long exposure' images was completely covered by the 'lens cap' image.

Then in the layers window, I selected the layer with the 'lens cap' image and changed the blending option to 'difference'. This is illustrated below.

And it worked! Amazingly, the speckle was removed. I was as chuffed as a Scotsman with a big bowl of Porridge. (And I am a Scotsman who loves a big bowl of Porridge.)

Let me remind you of the final effect...

Caveats...

This technique works pretty well with most long exposure images, but best with black backgrounds. Over lighter backgrounds, you will get blackspots - but these intrude into the image far less than the speckles.

For best results, whenever you take a 'long exposure' image, take a similar black image with the same matching ASA, shutter, aperture, and resolution. However you'll probably find that with some carefully chosen black images (at your most common settings), you avoid doing this every time.

Remember that with digital zoom, Fuji 'interpolation' comes into play - so the speckles will change position. In this case, you should take a corresponding black image afterwards to a ensure perfect match.

Final Thought

I no longer own a FP6900, and the hot pixel noise was one of the reasons. This technique is by no means perfect - but it helps.

Note: All images on this page were cropped from 3M resolution. They were not resized or altered in any other way, except using the techniques illustrated here.

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