Handbook for SXV-M5C Issue 1 August 2004
In some cases, there may be a difference in colour bias between the faintest and brightest objects. When this happens, first reduce the error of the faint detail, using the ‘START’ sliders, and then correct the bright ob jects by using the ‘MAX’ sliders. The ‘MAX’ slider allows you to vary the ‘slope’ of the transfer curve and so change the way that the balance alters from faint to bright detail.
Other options in the ‘Colour’ menu are ‘Apply Anti- Alias’ and ‘Adjust Chrominance’. We have already used the Anti-Alias filter as an option during colour synthesis, but it will be helpful for you to know its purpose. Basically, the AA filter is designed to remove colour errors at sharp transitions of brightness. Because of the spatial characteristics of the grid of filters on the CCD, a sharp edge in the image will overlay certain filters, but miss adjacent ones. When the colour synthesiser equations process the data from this region, there will be an incorrect result when these pixels are processed and a line of abnormal colour will follow the transition edge. This is well seen in images of stars, which often take on a strong colour bias, quite different from the expected star colour. The AA filter scans the colour image data and searches for fine details with rapidly changing colours. Wherever these errors occur, the filter substitutes the equivalent and equal values of red, green and blue, thus changing the deviant colour into neutral grey. The result is a much smoother colour image, with clean transitions around stars and other fine details. The AA filter may be used as many times as is desired, but its additional effects will be very slight after about 3 passes of the image.
The ‘Adjust Chrominance’ option is not needed for m ost images, but can be useful for removing atmospheric dispersion from images of the planets. ‘Adjust Chrominance’ permits you to move the red and blue frames with respect to the green frame and so compensate for the displacement of the colours caused by the atmosphere. To use the AC function, shift the red and blue images until the planetary disc has an evenly coloured periphery and any red and blue fringes disappear.
Enhancing your image:
