Processing

For processing the videos I initially used Astrostack, a simple program to learn. It is freeware and does as its name suggests, stacks images together to improve image quality (signal to noise ratio). It takes video (avi) files and registers all the images in a sequence so even if your drive is not perfect, and the target has wandered around a bit, it will correct for this. It has limited image processing, but once stacked the image can be "improved" elsewhere by further processing. This method, however, assumes all images in a video sequence are good enough to be used. The reality is somewhat different and better results can be obtained by taking a longer video sequence and then editing out all the poor frames. The software IRIS can do this automatically ("Align&Stack") and it is now my preferred software for both image taking and image processing. There are several alternatives such as K3CCDTools and Registax. Both are freeware and provide automatic/manual selection of the best images from a video (avi) sequence. Registax is particularly informative as to what it is doing and permits various degrees of user intervention (see Figure 3.7). My suggestion is to try them all and choose the one that works best for you.

Figure 3.10. Mars -RGB planes shown to scale. The vertical displacement is caused by the 3 color planes being differently refracted through the atmosphere. Most software allows this to be corrected during processing.

Mars 2003 - Philips Toucam Webcam Blue images

no infrared with infrared block filter block filter

Figure 3.11. Blue images of Mars 2003 without and with infrared block filter.

IRIS does not operate on color images in one operation but splits them into red/green/blue files, which then have to be processed individually before recom-bining them to form a color image. In theory, this is best, especially for typical northern latitudes where the planets are never overhead. The reason for this is that the three color bands are refracted through the atmosphere slightly differently so they are not quite in perfect registration (see Figure 3.10). Final processing can then correctly realign the color planes. The 2003 image of Mars split into RGB planes demonstrates this clearly. Mars was only 18 degrees above the horizon and the 3 planes were markedly at different levels.

Another issue that the 2003 opposition of Mars demonstrated was the need for an infra-red block filter (see Figure 3.11). The Toucam lens incorporates such a filter so when we remove the lens we remove the filter too (see Figure 3.12). The effect of this is infra-red light leakage - the blue plane especially is affected by this and produces a double image. The improvement in sharpness and color fidelity when using an infra-red filter is dramatic.

IRIS has a single command, which selects the best frames from a sequence, aligns them and then adds (stacks) them together (see Figure 3.12). This makes processing very painless but the operation can take up to 30 minutes of computing

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