Help me understand PL's Chromatic Aberration

[bruce1951]

I'm confused. No rude comments please.

I load a photo. Filter/Digital Camera/Chromatic Aberration. I'm getting terrible results. I'm getting a focus shift/blurred results. Rather than removing purple fringing is PL trying to 'undo' what the lens done?

So am I doing something wrong? Or is there another way of tackling CA? At the moment I'm using Hue/Saturation to take out the purple fringe. But that also is taking away 'purple' in areas that it is needed.

In PSP I can zoom in and select a bad area of CA. Then apply that colour selection. Works well and can target set colours.

So how to tackle CA in PL?

regards

[Hoogo]

Yes, there are different types (or effects) of chromatic aberration. One is a different size for each color (lateral CA), the other is a different focus (axial CA), and then there's purple fringing, most likely a kind of axial CA.

The CA-Filter in PL addresses only the error of different sizes, and it works when the edge to the center has the opposite color of the outer edge. There's no built in filter for the other problems, but there were some actions and receipts here in the forum.

[photoken]

Rather than removing purple fringing is PL trying to 'undo' what the lens done?

Exactly right. As Hoogo explained, PL is correcting for the lateral CA of the lens. The Help for CA correction explains how it does that by shifting the appropriate channels.

At the moment I'm using Hue/Saturation to take out the purple fringe. But that also is taking away 'purple' in areas that it is needed.

In PSP I can zoom in and select a bad area of CA. Then apply that colour selection. Works well and can target set colours.

What you're talking about is two separate effects: the lateral CA and fringing. You'll need to use different techniques for each.

I've found that for RAW images from my Lumix ZS100, which has mucho lateral CA, PL's CA correction works pretty darned well -- just make sure you disable it's "Width Compensation" option.

I did like PSP's method of targeting colour fringes (as you described). It was very straightforward to use. In PL, the equivalent is to use the Hue Editor (not Hue/Saturation) to attack fringing. You'll need to work in HIS mode, use the eyedropper to set a point on the graph (hold down the Ctrl key when clicking with the eyedropper to set the point on all three channels), and drag the point up or down on the graph(s) to correct the fringe. You can set multiple points and adjust them individually. The more extreme of a peak you create on the graph, the more limited the correction will be to the selected colour. (If you double-click on the icon for the "channel" at the top of the Hue Editor window, you'll get an enlarged graph to make things easier....)

The absolutely best way to deal with that situation for RAW images is to use RawTherapee. It has an automatic CA correction option which divides the image into multiple zones and applies differing amounts of CA correction to each zone before the RAW data is de-mosaiced. RT also has a Fringe Removal tool which is similar in operation to PL's Hue Editor, but is easier to understand and use and also works somewhat better for fringing.

[bruce1951]

Ken you have hit the nail on the head by suggesting attacking the issue in RAW. However I do a lot of post editing with HDR, NIK and Topaz plugins. The original file may have little or no evidence of fringing. However extra editing highlights/exagerates the slightest amount. And after many steps it's difficult to take the backward steps required.
Luckily PL allows me to use PSP as an external editor to address fringing/CA issues. I was just hoping PL had an function I had overlooked.

regards

[photoken]

Bruce,
The Hue Editor I mentioned is the tool you should experiment with.

Also, RawTherapee is not just for RAW images -- you can use its tools on TIF and JPG images, too (except, of course, for its RAW adjustments).

By the way, I put in a request for a dedicated fringe removal tool almost two years ago:
http://www.pl32.com/forum3/viewtopic.ph ... nge#p30852
using PSP and, more importantly, RawTherapee's DeFringe tool as examples.

[bruce1951]

Ken I tried RawTherapee some time back. Never liked it. Don't remember why but just didn't gel with me at all.

regards

[photoken]

Bruce,
FYI, I just did a quick experiment -- searched the Web for "purple fringing" and found this page with a link to a problem image:
http://www.pentaxforums.com/forums/10-p ... fault.html

Here's a comparison at 200% of the results using PL's Hue Editor:
The original:

fringe original.jpg

The corrected version:

fringe corrected.jpg

The settings used:

HE settings.jpg

[bruce1951]

Thanks Ken.
I'll have a play with it.

regards