0 Replies Latest reply on Mar 5, 2008 8:34 AM by (Yongzheng_Wu)

    How to quantify chromatic aberration?

      In Camera Raw, the chromatic aberration is specified as a integer in [-100,100], but I'm not sure about its quantitative meaning. For example, if I set red/cyan fringe to +100, how many percent will the red channel be larger than the other two channels?

      In www.photozone.de, CA is given as the number of pixels at the image borders. I guess the borders means the left and right borders in landscape orientation. For example, "2 pixels at the border" for a 3000x2000 image means 0.133% (2/1500). By the way, I don't think it is a good way to quantify CA because the same lens will thus have different CA value for different pixel density.

      In DCRaw, CA is directly specified as a enlargement ratio. Quoting from DCRaw manual: "-C red_mag blue_mag: Enlarge the raw red and blue layers by the given factors, typically 0.999 to 1.001, to correct chromatic aberration". It gives minimal ambiguity, and the same lens will have the same CA value no matter in full frame or APS-C, no matter in 8MP or 10MP.

      Come back to my question. I'm asking this because I already measured the CA of all my photos. Now I'm switching to Camera Raw, and want to make use of my old measurement. So I need a way to do the conversion.

      Thank you.