removing green and/or purple fringing?

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aloomens
Posts: 17
Joined: April 25th, 2009, 4:50 pm

removing green and/or purple fringing?

Post by aloomens »

What would be the best way to remove (or at least reduce) green and purple fringing? I initially thought to use the Chromatic Aberration transform, but that has controlls for red and blue shift. Any suggestions would be welcome. Thanks.

aloomens
Posts: 17
Joined: April 25th, 2009, 4:50 pm

Re: removing green and/or purple fringing?

Post by aloomens »

I've played with this a bit (PWP5) and had success removing the fringing using the Color Correction transform. However this also affects other areas of the image, so I guess I need to use a mask. In the Color Correction transform, there are check boxes for Show Affected Region and Save as Mask. I select these, and the preview window becomes a good starting point for a mask. How do I save this preview window as a mask?

aloomens
Posts: 17
Joined: April 25th, 2009, 4:50 pm

Re: removing green and/or purple fringing?

Post by aloomens »

Yes, that's exactly what I would expect, however if I click Apply or OK, the resulting image is in full color, and is not the mask that I saw in the preview window.

I've tried this over and over again. I select the Color Correct transform, make the original image 1:1, click on the color I want to remove, then in the transform I click on Show Affected Region, and Save As Mask. When I click OK or Apply, it gives me a full color image and not a mask. I must be missing something simple, or it's just not working.

den
Posts: 850
Joined: April 25th, 2009, 6:33 pm
What is the make/model of your primary camera?: Canon EOS-350D/Fuji X100T
Location: Birch Bay near Blaine, WA USA

Re: removing green and/or purple fringing?

Post by den »

aloomens wrote:...In the Color Correction transform, there are check boxes for Show Affected Region and Save as Mask. I select these, and the preview window becomes a good starting point for a mask. How do I save this preview window as a mask?...
Click Apply or OK when a control point is 'active'. If there are multiple control points, you could create a mask image using Apply for each of the control points, then preferentially combine them into a single mask... ...but this may require closing the Color Correct transform to use other transforms when combining the mask images... ...then re-open Color Correct and selecting the composite mask as the Amount mask.

OK... the above is an edit to a posting I deleted prior to "aloomens'" above post...

PWP5's Color Correct works as described above as does PWP6's. Try (1) closing the Color Correct transform and re-opening it; or (2)closing the program and re-opening it: and (3) perhaps even a system 're-start'. I have sometimes [rarely] had transforms become unresponsive after extremely prolonged sessions.
Last edited by den on August 7th, 2012, 11:33 am, edited 1 time in total.

aloomens
Posts: 17
Joined: April 25th, 2009, 4:50 pm

Re: removing green and/or purple fringing?

Post by aloomens »

OK, I see what was going on. When I clicked on either Show Affected Region or Save as Mask, it would switch focus to the preview window. When I then click on the transform window, to switch back to it, so that I can click OK, it made the control point not active. What I have to do instead it to move the preview window out of the way so that I can click OK on the transform window without deactivating the control point. Kind of counter intuitive.

Thanks Den, for all the help you've provided on the this forum!!!

den
Posts: 850
Joined: April 25th, 2009, 6:33 pm
What is the make/model of your primary camera?: Canon EOS-350D/Fuji X100T
Location: Birch Bay near Blaine, WA USA

Re: removing green and/or purple fringing?

Post by den »

Going back to the OP and the PWP's Chromatic Aberration transform...

A 'mouse off/mouse on' example of its use on an uncropped; minimum initial edits to: brightness, contrast, colors, and sharpeness; image version is shown as Illustration 5 near the bottom of the web page here: http://www.ncplus.net/~birchbay/dcraw/v ... /index.htm.

(1) when PWP's Chromatic Aberration transform is 'active'... ...read through Kiril's "F1 Help"...
(2) chromatic aberration reduction due to lens distoration seems to be 'best' when performed before cropping and any substantial edits are made to tone/colors/sharpness as these will only 'enhance' the aberration.
(3) for my camera and lens combination, I find that an adjustment where the the 'Blue shift' is half the 'Red shift' seems to be the most 'generic'... ...so I will adjust Red until the magenta is minimal, then adjust Blue to half of that while monitoring Preview with a Zoom-Factor of 3 or 4:1 of an edge or corner image area...

Further investigation has resulted in my conclusion, that if the Chromatic Aberration reduction occurs in the 'dcraw.exe' RAW conversion using the " -C red-shift blue-shift" option, the reduction is even further improved then with a minimumally tone/colors/sharpness converted tiff image version.

For those who would like to explore this 'dcraw.exe' option, here is a table of values where the 'Blue-shift' is half of the 'Red-shift':

"dcraw.exe -C <r b>" Correct chromatic aberration
-C 0.99800 0.99900
-C 0.99825 0.99913
-C 0.99850 0.99925
-C 0.99875 0.99938
-C 0.99900 0.99950
-C 0.99925 0.99963
-C 0.99950 0.99975
-C 0.99975 0.99988
-C 1.00000 1.00000 ...Default (no correction)...
-C 1.00025 1.00013
-C 1.00050 1.00025
-C 1.00075 1.00038
-C 1.00100 1.00050
-C 1.00125 1.00063
-C 1.00150 1.00075
-C 1.00175 1.00088
-C 1.00200 1.00100

...have fun... ...den...

aloomens
Posts: 17
Joined: April 25th, 2009, 4:50 pm

Re: removing green and/or purple fringing?

Post by aloomens »

Yes, it is fun! I've just started playing with dcraw some too.

FYI. There is program distributed with "hugin" that is supposed to be able to "automatically calculate lens chromatic aberration correction parameters".

The bottom of this page explains how to use it to calculate parameters for dcraw:
http://wiki.panotools.org/Tca_correct

Haven't had time to play with it yet, though.

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