| Purple Fringing |
Article Index for Purple |
Website Links For Purple |
Information AboutPurple Fringing |
| CATEGORIES ABOUT PURPLE FRINGING | |
| science of photography | |
| digital photography | |
|
In Photography , and particularly in Digital Photography , purple fringing is the term for an out-of-focus purple ghost image on a photograph. Images taken with high-contrast boundary areas involving daylight or gas discharge lamps are particularly susceptible, since Chromatic Aberration is worst for the shortest wavelengths that a camera is sensitive to (violet and/or ultra-violet light). The term ''purple fringe'' to describe one aspect of chromatic aberration dates back to at least 1833, before the invention of photography.1 However, Brewster's description with a purple fringe on one edge and a green fringe on the other is a ''lateral'' chromatic aberration. A general defocus of the shortest wavelengths resulting in a purple fringe on all sides of a bright object is the result of an ''axial'' or ''longitudinal'' chromatic aberration. Quite often these effects are mixed in an image. Axial chromatic aberration is more subject to reduction by stopping down the lens than lateral chromatic aberration is, so the purple fringing can be very dependent on F-number . OTHER EXPLANATIONS Purple fringing is usually attributed to Chromatic Aberration , although it is not clear that all purple fringing can be explained this way. Other attributed causes of purple fringing include:
MITIGATIONS Commonly advocated methods of avoiding purple fringing include:
Post-processing to remove purple fringing (or chromatic aberration in general) usually involves scaling the fringed colour channel, or subtracting some of a scaled version of the blue channel. REFERENCES Other sources
|
|
|