Chromatic Aberation only showing up in HDR shots

zombiemann · Aug 30, 2012

I seem to be having a real issue lately of CA showing up in my HDR shots. The shot I am posting is just for example, not C&C. It was made from 9 exposures (needed elsewhere in the overall shot). I put them together in photomatix, and tone mapped using a fairly "tame" preset. My question is, how can I avoid this? Is it a product of incorrect number of exposures, a possible product of f-stop (needing to shoot "higher" like F8, I normally shoot as low as the lens will go, around 3.5. I'm still learning and didn't know until today that could cause sharpness issues and contribute to CA)? Any ideas or constructive thoughts on what I could do different?

unpopular · Aug 30, 2012

Is that a crop or something? Unless you're using a magnifying glass as an objective, I don't think that this is CA ...

In any case, CA is affected by aperture, and is probably emphasized by tone mapping - Bynx or VIP would know better. But this seems REALLY extreme. What do your source files look like?

Bynx · Aug 30, 2012

In Photomatix there is a checkbox to address CA. Its usually bad when there is strong light against strong darks. But I did notice the CA glow you had in your night street scene. I wonder how much CA is affected by the lens, the lighting, or the processing. When shooting try to keep your aperture between f8 and f11. If you have your lens wide open I believe that could be a problem with stray light causing problems.

zombiemann · Aug 30, 2012

yea this is a crop of an overall shot to show the "bad" areas. I didn't see anything the first time through on the source files, but upon closer inspection it is there... but you have to zoom way in to see it (300% or higher). So I am guessing that it is a product of aperture accentuated by tone maping.

zombiemann · Aug 30, 2012

Bynx said:
In Photomatix there is a checkbox to address CA. Its usually bad when there is strong light against strong darks. But I did notice the CA glow you had in your night street scene. I wonder how much CA is affected by the lens, the lighting, or the processing. When shooting try to keep your aperture between f8 and f11. If you have your lens wide open I believe that could be a problem with stray light causing problems.

I am going to go down tonight and reshoot the street scene with a higher f-stop and we'll see if that fixes it. I'm going to try duplicating this shot as well. If it does fix it, I have a bunch of shots to retake because I've scrapped them. Oh well, it's a learning process. The day I stop learning is the day I stop breathing.

Bynx · Aug 30, 2012

If its any consolation, as many HDR images I have shot, Im still learning each and every time. But I just feel more comfortable when doing it.

vipgraphx · Aug 30, 2012

There are many issues why CA is present in photos. Lets start with a list

1. Lens - cheap lenses will have more CA than quality glass, usually the number one issue..Need to look for lenses with aspherical lens inside!
2. The light to dark contrast
3. A

perture

and lighting

What happens in merging files in photomatix. Even when you select the box it still can come up. The process of tonemapping amplifies certain areas because the algorithm in the software is doing its best to keep all the info in. This is why can give off that fake looking vibe. Even our own eyes do not see all the details in every area of a picture. Now depending on the sliders your using can also amplify the CA. Its almost something one can not avoid with certain image conditions.

Solution is knowing how to fix it!!

One is learning how to manually blend images in photoshop so you do not have to tone map however this will take that "HDR" look away and replace it with a realistic photo looking image.

If you like the "ToneMapped" "HDR" look then you have to know how to remove it and usually it is very simple once you know how to.
I will explain the best I can. Hopefully you are familiar enough with photoshop.

1) get your selection tool and drag around the area with the CA. The CA can range from red,blue, magenta and green. These are the most common but the Magenta is the most.

2) go to image/adjustments and select hue and saturation. Now choose the color from the drop down menu like blue or megenta and move the saturation slider to the left then adjust the darkness to the left. You may have to use a few color if the CA has multiple colors in it.

You should be looking good by now.

In your photo I would almost bet it has a combo effect on your lens and the HDR processing more than anything.

here is the final result

zombiemann · Aug 30, 2012

Fortunately I am pretty stubborn. The fact that I have OCD helps as well. Repetition doesn't bother me in the slightest, so I will shoot something until I get it right, even if I have to keep going back for weeks adjusting things each time I go. There is a building downtown that I have always loved the look of, ever since I was a kid. One of these days I am going to get a solid night shot of it without the lights being all blown out

Just a matter of trial and error until I figure it out. Most of the time I struggle to learn by reading, so trial and error is the best way for me to go