Gradation Curves

If dark areas of a video are too dark, the Gradation Curves VirtualDub filtere can be used to brighten them up, without changing light and mid tones. The filter can invert the color space like the internal invert filter and can apply coring, like the coring filter plugin that exists for VirtualDub. If the tone of a video is, for example too blue, the filter can be used to compensate this.

The overall brightness can be changed also. Perhaps the filter can also be used for some scientific use, if there is a need to mask a certain color. And the good thing is that it can all be done at the same time with one filter instance only. The filter also gives the possibility to apply curves in other color spaces. Using the HSV space, individual colors can be exchanged by other ones or/and the saturation can be changed for example. But note that one filter instance can always only process one color space.

If a manipulation in RGB and HSV space is needed, the filter has to be put into the filter chain two times: once for RGB processing and once for HSV processing. Other possible applications of the filter include: • Use of the filter as prefilter of the deshaker filter for difficult (dark) DV Cam captures in the first pass of deshaker. Some colors can be masked, so the motion analysis works better in the first pass of deshaker. • Use of the filter in the area of "film look for DV material". See posts in the doom9 forum or the VirtualDub forum.

The x axis of the curve represents the input color value, the y axis represents the output color value. Initially the filter will show a 45° left down to right up curve. This signifies that the output color will be the same as the input color for all color values. Raising the output value, results in a lightning up of the selected input color value. The filter always stores the settings of five gradation curves, even if only the RGB curve is used. This way the settings of the R/G/B curves are not lost if, for example temporarily RGB only mode is used and the processing settings are saved at that time. The fifth curve is only used for the K channel of the CMYK color space.