I may continue the EFB work later, which is mainly for calibration and test purposes, to prepare for PJ (perijove) image processing. But now I'm curious about the Jupiter approach images, and hence uploaded the efb12 version as it is I'd think, that another improvement of accuracy by a factor of about 5 to 10 should be possible. Moving the optical axis a few pixels along x can help to improve registering the area near Earth's "left" limb. Moving the optical axis along the y-axis with respect to the nominal value didn't result in significant improvements either. I've tested for an aberration due to a possible minor rotation of the camera around the z-axis with respect to Juno's rotation axis, but it's probably less than 0.1 degrees I failed to resolve the small inconsistency that way. good result for the other parts of the image. But for the x/z scale I've an unresolved inconsistency of about 0.5% to obtain a good result for the overlap region vs. I've introduced a small Brownian K2 to improve the registering in the overlap region a bit.
Junocam colorcast how to#
So, I'm open to suggestions, how to improve color calibration - or about which image data are required by others to improve the images I'll hopefully be able to provide. My focus thus far has been - and will stay for some more time - improving geometric calbration. But it seemed, that there doesn't exist a consensus how to color-calibrate telescopic Jupiter images.
I had also a short discussion with astronomers about using telescopic Jupiter images as a color reference. The easier way is deriving the weights by comparing EDRs with linearized RDRs, to get consistent with the MSSS calibration, or using RDRs directly, with the constraints, Mike mentioned. Necessary would be a color-correct Earth image of exactly the same time and perspective to infer the best color correction matrix. So, using Earth as an inflight color-calibration target, instead of Moon is principally an option, with the above limitations regarding various sources of color casts.
The color filter characteristics might change with light incidence angle this effect seems to occur at least for the CH4 band, if I interprete the respective section in the JunoCam paper correctly.Īnother effect might be the slightly greenish cast of sunlight outside Earth's atmosphere, but I'd think, that this effect should cancel out with Moon's color. Then, the color band spectra are different from human color receptor sensitivity spectra.
Junocam colorcast full#
Next, I didn't use a full 3x3 matrix linear color correction, but only use the main diagonal, i.e. For colors which are dark in at least one band might be sensitive to small inaccuracies of dark current subtraction and other image noise. Then, small shifts in perspective seem to be sufficient to change the apparent brightess of the target and hence of the color bands, resulting in color casts. And there might be some smear and stray light contributing to a color cast this latter effect will be much less at Jupiter. The images are also not yet flat-fielded I've no explicite flat-field, and didn't yet try to derive a flat field this might shift colors slightly, too. I might refine the weights later, after measuring Moon's color accurately.
I've derived a color scaling from the EFB01 Moon image. The images of the above synopsis are rendered from the EDRs, and without additional gamma correction, so gamma = 2.0.
0 kommentar(er)
