Halos! Why they occur and how to avoid them...
05-07-2012, 05:28 PM
I'm wondering if you can share some information about halos...
Why they happen in the first place and how to make sure you don't have them in your images...
Also, and maybe you've experienced this too, when I look at pictures of birds against a plain light-colored background, I can often see a glowing white aura around the bird...even if I've barely processed the image I can see it there, but only when I look at my screen from the top, or sideways, and so forth...any ideas?
Thanks so much for your input! It's much appreciated!
PS As an example, here is my most recent "Avian" post...
Last edited by Jack Breakfast; 05-07-2012 at 05:36 PM.
05-07-2012, 08:33 PM
I don't think you're crazy because I can see it too. Thing is, it seems to change thickness and I can actually see it reduce in size (especially around the head). Mostly noticed upon first look as my eyes seem to adjust to scene. I've seen this explained somewhat in some of those optical illusion things you can find on the web but don't have a link for you. This halo is different than the kind you'd get with overly zealous PP (shadow/highlight work) as those kind don't go away.
05-07-2012, 09:22 PM
Steve I was thinking about the illusory happenings with the black on white or black on light blue and how 2D can look 3D at times, etc etc etc. I keep my shadow & highlight work to a minimum, so I'm not too worried there. I'm told one can see halos when one oversharpens as well. But as for my example photograph, the halo comes and goes...very strange indeed, and I'd love to read/learn more about this...if anyone has any ideas...
Also: thanks so much for writing...
05-07-2012, 09:25 PM
I don't see any halos in your posted image. I looked at it on both a calibrated monitor and an uncalibrated laptop.
Lens flare can cause halos, as can processing (either in camera jpegs or raw conversion) as well as post processing. Probably monitor response can cause it too, and perhaps one's eyes. We also seem to be more sensitive to a bright halo and less so to a dark halo. But I would say is is most commonly due to processing, or maybe it just often comes out stronger and more noticeable with post processing.
05-07-2012, 11:38 PM
Good stuff Roger and many thanks for sharing your erudition and good ideas...much appreciated...
05-08-2012, 02:07 AM
Hi Jack, I've been asking myself the same question for some time now.
I must say that I don't see a halo around your gull. I'm viewing it on an uncalibrated laptop that I use for all my image processing. I especially had problems with halos emerging around trees against a blue sky in landscape images after PP (I don't shoot that many birds). After paying specific attention to this problem while processing several of those images, I came to the conclusion that the halos emerge in any editing involving contrast adjustments. I use contrast and clarity adjustments to bring out more detail in clouds, usually by using the grad filter in ACR6.4, which also covers part of the tree. As you mention, also sharpening actions cause halos. These (at least the USM that I normally use) work by increasing microcontrast, apparently with the same result.
Contrast adjustments increase the difference (levels) between light and dark areas, so they will make light areas (such as sky) lighter, and darker areas (bird, tree) look darker. Especially microcontrast adjustments will work strongest on edges (that's why we perceive images adjusted with USM as sharper). So on areas where you have a dark subject against a lighter background, or a darker line at the edge of the subject (as in your gull), contrast adjustments may lead to halos when excessively applied. My bet is that some halo must already be present in the original image. I can imagine that diffraction can play a role for remote subjects, but maybe Roger can expand on that better than me.
05-15-2012, 09:01 PM
I must be missing something, I can't see any halo's. I'm using a calibrated NEC monitor and CS5.
05-15-2012, 09:51 PM
I am on a calibrated mac book pro. I am unable to see any halos on the referenced image. The fact that some see halos & some don't suggests to me that the monitors are responsible.
05-16-2012, 07:53 AM
But I'm only using a calibrated HP 2311x flatscreen.
05-16-2012, 09:20 AM
Many thanks to everyone for writing in...your time is much appreciated by y.t.