Incense

by Bart Arondson

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I recently discovered my girlfriend's (relatively cheap) camera has a long-shutter night mode. With this I made a few light writing experiments.

For instance like this:

enter image description here

Basically, the bad thing about the camera I'm using however is that the max shutter time is only 16 seconds, a relatively short time for light writing.

So, is it possible to "combine" two light writing photos so that there is more time available? Also, out of curiousity, is there any way of emulating a long-shutter mode for the purpose of light writing with a camera without a long shutter mode, such as my cell phone? (combine the frames of a video into a single picture or something?)

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2 Answers 2

Provided there is no gap between exposures, there is no difference between recording one long exposure in which light is collected and measured, and taking two short exposures and adding the collected light values together.

The problem occurs when you have gaps in time between exposures, as this will cause, for example gaps in the writing. If you use separate exposures for each word you ought to be able to add hem together into more extensive light writing images.

Whether you can do this with videos from your phone depends on the "shutter angle" which is an old fashioned term for how long each frame is exposed for compared to the duration between frames. I suspect phones use a 360 shutter angle, i.e. the frames are exposed for the maximum amount of time, with no gaps. This means you should be able to add the frames together to get light writing with no gaps, it then becomes an exercise in scripting to split the video to frames and add them together.

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just adding two photos reduces SNR by factor of 2. The backgrounds add in unwritten areas and you also get background A + writing B added. If yo can pick out the highlight only (eg mask to a certain brightness level) then you can maintain SNR. –  Russell McMahon May 27 '12 at 21:37

First - your light writing question:

I assume you're looking to be able to say write HELLO WORLD and let's say that 16 seconds gets you HELLO.

Then - yes, you could hit the shutter again and provided you know where you left off continue writing your next word.

What you want to do is get it pitch black. It looks like you left the hall light on which is why you can see the room and a ghost of yourself. The less light, the more your writing is the only thing visible, and you're not worrying about matching other parts of the picture up later.

Then you'll need photo editing software where you can piece the two images together and erase half of the second one so you can see the part of the first that is different. GIMP is a good free program - and Photoshop is a popular but expensive program - that allows layering of images and masking off sections.

Tutorial example (check out part III specifically) http://photo.net/learn/digital-photography-workflow/advanced-photoshop-tutorials/layer-masks/

As for the second part:

I don't know what phone you have - but depending on the model there may be apps you can download that allow for manual control of the camera.

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