Purple Fringing

[tomczak]

There were discussions on the nature and remedies for Purple Fringing, but I can't find them anymore. Did we have an automated method that could minimize them? There is a PS (not really automated) method below; have someone translated it to PWP? Are there any other ideas? What really causes the purple fringing? Cheers.

http://www.great-landscape-photography. ... nging.html

[Charles2]

Click on Search Archive, search for
purple
and
fringing
Select "and" instead of "or"

Several threads will come up.

[den]

Currently with PWP5 and depending upon image content, I have been experimenting the neutralization of ''purple fringe' by:

Step1: create an edge mask limited to the 'fringe' image area(s) by: (a) using the Mask Tool - Paint (All Pixels) tool with a medium radius and soft-side at 0% transparency; 'Add' paint the 'purple fringe'; and (b) Overlap 'lower-left' Apply a texture that finds edges.

step1a.jpg (40.88 KiB) Viewed 6709 times

step1b.jpg (45.69 KiB) Viewed 6708 times

Step2: Use the Step1 mask with: (a) the ColorBalance transform with Auto White/Black de-activated and selected 'purple fringe' mid-tone neutralizing color pairs; or (b) the ColorCorrect transform with 'purple fringe' control point arrows extended to the 'white point' with anchoring control points surrounding the 'purple fringe' control points. Usually the brightness of the neutralized 'purple fringe' control points will need to be decreased by about 10%; or (c] the Remap transform with 'purple fringe' color pairs. Switch the Remapped Color dialogues from RGB to HSV and set S=0 [and usually decrease V by 10%]. Adjust transform sliders to preferences....

...or...

As in the case of the illustration image content: use the Remap transform with 'purple fringe' color pairs. Switch the Remapped Color dialogues from RGB to HSV and set H= (n-33) [changes the blue-purple to green-cyan] and adjust the color dialogue/transform sliders to preferences....

All rather manually intensive.... anyone else doing it differently?

[den]

In reviewing my notes... I would like to offer an alternate Step1 mask workflow as the originally suggested mask applies changes equally to the lighter saturations/tones and to the darker saturations/tones at the PurpleFringe edges.

The following mask will allow changes more strongly to the darker saturations/tones and less so to the lighter saturations/tones which may be more suitable for PurpleFringe reductions....

Alternate Step1: create an edge mask limited to the 'fringe' image area(s) by: (a) using the Mask Tool - Paint (All Pixels) tool with a medium radius and soft-side at 0% transparency; 'Add' paint the 'purple fringe'; (b) Overlap 'lower left' Apply a BrightnessCurve=[0,100], [100,0] and (c) Overlap 'lower-left' Apply a texture that finds edges.

[den]

If the suggested Alternate Step1(b) "Overlap 'lower left' Apply a BrightnessCurve=[0,100], [100,0]" provides insufficient change, try: "Overlap 'lower left' Apply a BrightnessCurve= BrokenLine [0,100], [50,100], [100,50]".

This Overlap BrokenLine curve will apply full strength change to the 0-50% tones of the PurpleFringe edge with gradually decreased strength to a 50% change in the 50-100% tones of the PurpleFringe edge.

If of interest, a web posted version of the image used for the mask illustration is the top image here [2 images - 750KB]: http://www.ncplus.net/~birchbay/10/IMAG ... _10_90.htm and some recent early fall color landscape images [5 images - 2MB] here: http://www.ncplus.net/~birchbay/10/IMAG ... _10_89.htm. All had some degree of purple fringe reduction although this is not apparant at the web resolutions.

Ask if there questions....

[den]

MaciejT... and Others

A last suggestion and this is one you will have to try on your own image and 'pixel peek' as the posting resolutions really do not show this approach to best advantage... and it is easier to do then previous Step2 suggested alternatives....

Step1: again use the Mask Tool to create an edge mask limited to the PurpleFringe image areas and leave it active on the image... if the last mask action is Overlap 'lower-left' Apply a texture, one can 'Undo', move the Texture white slider left or right, and Overlap 'lower-left' Apply the new texture to adjust edge widths to a preference.

Ex2_Step1_applied_edge_mask.jpg (48.81 KiB) Viewed 6478 times

Step2: click on the image and open the Color Curves transform. Form a HSV-V curve = [0,0], [100,75] and a HSV-S = [0,0], [100,0]. Set the transform mask White Amount = 50% and mask Black = 0% [default]. Click OK.

This step lowers contrast, darkens, and partially de-saturates by 50% the masked PurpleFringe image edges. If you 'pixel peek', both the bright 'purple' and bright 'aqua' will be reduced to perhaps acceptable levels that at normal viewing/printing resolutions will not be detracting without objectionable loss of apparant edge sharpness... an un-avoidable trade off which may be recovered with followup sharpening.

before-after_2-1_400px.jpg (45.41 KiB) Viewed 6476 times

That's it... I am out of ideas!!! Ask if there questions...

Question: Is anyone using the ChromaticAberration transform for PurpleFringe reductions?

[tomczak]

Many thanks, Dan and Charles. All the Dan's techniques are cool and doable. I was hoping for something maybe more crude, but automated. The best I could think about was the Edge widget with the Action=lighten/darken and some relatively small amount value. The problem is that this is typically a little too crude as it obliterates some other edges that shouldn't be touched.

I don't quite understand the mechanism of purple fringing, but most of it should probably be in the Blue channel. Would it do any good to extend the Colour Space of the edge widget to individual channels add 'increase/decrease saturation' option to the Actions drop-down list? This way one could automatically desaturate the edges in blue channel only. It seems to work reasonably well for a few images, but I need to try it a few more times to make sure.

BTW: would someone know exactly what is the mechanism of the purple fringing?

I did try the Chromatic Aberration on purple fringes, with some succes, but I suspect that this was a combination of chromatic aberration and purple fringing that I was removing, and thus I thought I was successful.

[den]

The previously illustrated Step1 masks are relatively easy to create because the PurpleFringe [PF] edges are contrasted against nearly homogenous backgrounds but what can one do where the background has complex tone/colors and PF occurs in non-silhouette image areas?

A suggested technique would be to: (1) use the Mask Tool - Color Range feature to Add 'lower-left' Apply PF tones/colors; (2) 'lower-left' Apply a small Blur [optional]; and (3) Overlap 'lower-left' Apply a Texture that finds edges...

The following is a suggested PF tone/color reference image for download that will set the Mask Tool - Color Range white sliders:

PurpleFringe_HSVColor-ToneRange.jpg (13.75 KiB) Viewed 6376 times

(1) Click on the reference image and open the Mask Tool - Color Range feature. Left mouse click on the center Purple color and click on 'Contract'. Starting with the center Purple color, left mouse click-hold-drag into the dark and light color regions ending in the center Purple region to release the hold. This sets the ColorRange white sliders.
(2) Feather the color selection by moving the black sliders as illustrated below.

PurpleFringe_MaskTool-ColorToneRange.jpg (40.95 KiB) Viewed 6378 times

Close the Mask Tool. The ColorRange settings will remain unchanged during a single PWP5 session.

Click on or open an image to be masked. Open the Mask Tool - ColorRange feature and Add 'lower-left' Apply. Optional: 'lower-left' Apply a small Blur [usually Blur=1 is sufficient]. Overlap 'lower-left' Apply a Texture that finds edges. Leave the Mask Tool 'active' on the image.

Then proceed with preference PF neutralization using ColorBalance or ColorCorrect or Remap or ColorCurves or ....

[tomczak]

I tried one more technique in addition to Den's procedures: after masking the purple fringes by Mask/Colour Range + Texture, you may want to try Filter transformation. I found that choosing the right Filter Colour (similar or more saturated/blueish than the fringes), checking Complement box and adjusting Exposure Compensation can remove the purple while maintaining the brightness similar to the areas adjecent to the fringed edges.

[den]

MaciejT....

(1) I tried the masked edge Filter-Compliment+ExposureCompensation approach on two test images... but I had a strong tendency to add a compliment Aqua cast to the lightly saturated Purple Fringe that I was trying to eliminate... propbably did not strike the right balance for the filter color, EC, and transform amount....

(2) If you will, please try the following on your test images and comment....

Noticing that a lesser 'Aqua' Fringe usually will accompany the 'Purple' Fringe, I created a revised reference image for download to set the MaskTool-ColorRange white sliders. This revised image includes Purple+Aqua. Preset the MaskTool-ColorRange white and black sliders in the same manner as previously suggested/illustrated and close the MaskTool...

aPurple-AquaFringe_HSVColor-ToneRange.jpg (17.82 KiB) Viewed 6215 times

then:

1. Open or click on the image to be masked;

2. Open the preset MaskTool-ColorRange and 'lower-left' Apply; then Overlay 'lower-left' Apply an edge Texture leaving the mask 'active' on the image. Adjust the Texture black/white sliders as needed when Previewing adjustments in '3.' below; and

3. Click on the image and open the ColorCurves transform. Form a HSV-V Gamma curve = [0,0], [50,30], [100,80] and a HSV-S BrokenLine curve = [0,0], [100,100]. Initially set Mask white = 75% [usually re-adjusted to 100%] and black = 0% Amounts. While monitoring Preview, adjust Mask white and the HSV-V curve [usually no change preferred] to preferences... then click OK.

The above seemed to generically work well for my test images, how about on yours? or anyone's?