Making Video with Photoshop

To make a video out of a set of raw exposures you need a program to process the shots first and convert them to tiff format, then Photoshop can be used to process them further.

I used Nebulosity to apply bias, darks and flats as usual to all the frames. Then they were debayered (converted from raw to color) and their intensities were normalized using 'normalize' function in Nebulosity in an attempt to eliminate differences in background brightness.

The differences in brightness, especially in background, seem to be the biggest problem in processing frame sets into a movie. It takes long time to shoot all the frames, usually 2-3 hours, during which sky brightness may change a lot due to time (lights being gradually switched off) or weather (change in transparency). Without eliminating these differences it is very difficult to process them automatically in Photoshop using curves and levels. My last comet movie consisted of 148 frames, so manual processing was out of question. Nebulosity normalization helps, but usually does not eliminate this problem completely, and the final fix must be done in Photoshop.

Before processing further in Photoshop the frames were converted into tiff with 'Batch Convert' in Nebulosity and copied to a new directory. In order to do automatic processing in Photoshop it is best to place all the pictures in one directory and then use "File"->"Automate"->"Batch" to process everything in it. But first all the steps must be recorded in a Photoshop action. Recording an action is easy ("Actions"->"New"), but the frames must be very similar in order to use automated levels and curves. If they are not, the result is either very bright background or very dark picture with most of the shadows cut off.

My way of equalizing frames is to prepare a layer that contains only minimum background brightness, and then subtract this layer form the main image. This way I end up with very similar frames, since the more ambient light in the frame the brighter minimum background layer becomes. The way to do it is to duplicate main layer, apply maximum "dust and scratches" filter (100px) to eliminate stars, comet and other stuff, and then iterate through a few "minimum" filters (3 at least) to remove whatever is left of comet. Once I end up with an uniform layer approximately equal to a background brightness of the master layer I use "Apply Image"->"Subtract" from the master layer to subtract background. Now it is possible to use levels and curves as usual to bring the comet forward, adjust colors and saturation, and of course resize image to a more appropriate size for a movie. Here is the action I recorded for the comet Garradd. This action is an example - it must be modified to match your frames.

Once  the action is ready it can be applied to all frames using "Automate" - the results will be in a new directory. It may take a lot of time to process frames - my 148 comet Garradd frames took about 10 hours.  The last step is to generate actual movie: "File"->"Open As", selecte the first processed frame and check "Image sequence" at the bottom, then "File"->"Export"->"Render movie". It is usually necessary to play with parameters like movie format and compression a bit to produce best results. And it is now ready to upload to YouTube!