Purple fringe?

SS
Posted By
Sol Sert
Aug 19, 2006
Views
462
Replies
6
Status
Closed
Hi
My digicam generally delivers great pics, BUT like many other cameras it suffers from blue/purple bleed in high contrast areas especially next to highlight. I know, you can buy plugins for PS, but has anybody written a macro, he or she will share?
I’m interested to know how it works, if possible.

Regards
Sol

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B
bmoag
Aug 19, 2006
It is not clear if you have CS2 which has a filter for this in the raw converter and the filter/distort/lens corrections.
There are some free plug-ins, alas I no longer have them but they are easy to find, which do the same thing.
However the effectiveness of these color shifting filters is often marginal, particularly for trying to correct the fringe around a large hard edged picture element, and they can introduce problems as well as solve them. Sometimes some deft use of the clone or healing brush is required.
SS
Sol Sert
Aug 19, 2006
Using PS 7 (Danish), alas!
Naturally I have searched The Net, but to no avail…
MR
Mike Russell
Aug 19, 2006
"Sol Sert" wrote in message
Hi
My digicam generally delivers great pics, BUT like many other cameras it suffers from blue/purple bleed in high contrast areas especially next to highlight. I know, you can buy plugins for PS, but has anybody written a macro, he or she will share?
I’m interested to know how it works, if possible.

Color fringing is caused by an optical defect in the lens design that causes different colors to be refracted differently. The result is that the red, green, and/or blue images are different in size, with red being largest and blue being smallest. Fringing typically shows up in the upper corners of an outdoor image, where the horizon or foliage is silhouetted against the sky.

The quick fix is to use the sponge in desaturate mode to get rid of the unwanted colors, but this is a crude solution at best. A more accurate improvement is can be done by resizing the red and/or blue channels slightly to match the green channel, which is used as a reference.

Here’s a procedure for versions of Photoshop that do not have the Distort>Lens Correction filter. Use the magnifying glass to zoom in on the most extreme area of fringing. Click on the channels, palette, highlight the red channel, click on the "eyecon" for RGB to view the color image, Select All, and select the Edit>Transform tool to minimize the fringing. Repeat for the blue channel.

Magenta/green fringing is fixed by resizing the red channel. To remove any magenta fringe is on the outside of the object, (or green fringe is from the inside) make the red channel smaller. When you are done resizing red you should have either no fringe, or a blue/yellow fringe. If you have a blue yellow fringe, make the blue channel larger as necessary. Use the numeric text fields to enter the zoom setting, since you’ll be working down to the tenths of a percent.

Mike Russell
www.curvemeister.com/forum/
SS
Sol Sert
Aug 20, 2006
What you are describing is normal *chromatic abberation*, caused by imperfections of the camera lens. I believe *purple fringing* is a slightly different problem. Some have proposed, that it is caused by the narrow angle, light reaches the microlenses in front of the CCD elements close to the edge of the chip. It increases with the degree of contrast and in worst case it much wider than normal chromatic abberation.
By the way, the plugin PTLens is great to compensate for chromatic abberation, but *NOT* for purple fringing.
MR
Mike Russell
Aug 20, 2006
"Sol Sert" wrote in message
What you are describing is normal *chromatic abberation*, caused by imperfections of the camera lens. I believe *purple fringing* is a slightly different problem. Some have proposed, that it is caused by the narrow angle, light reaches the microlenses in front of the CCD elements close to the edge of the chip. It increases with the degree of contrast and in worst case it much wider than normal chromatic abberation. By the way, the plugin PTLens is great to compensate for chromatic abberation, but *NOT* for purple fringing.

You are correct – purple fringing is another animal, and there is a procedure in Photoshop for dealing with using the Hue/Sat adjustment to desaturate the specific shade of purple:
http://www.pcworld.idg.com.au/index.php/id;154451015;fp;2;fpid;1585691688

Photoshop 6 and later support the ability to change an adjustable range of hues via the Hue / Sat command. Set the edit field to Blue, then use the eyedropper to zero in on just the hue of the purple fringe. Adjust the sliders at the bottom of the Hue / Sat window to select only the narrow range of purple you need. Drop the saturation to about 80 percent or so to reduce the fringing.

Mike Russell
www.curvemeister.com/forum/
K
KatWoman
Aug 22, 2006
"Mike Russell" wrote in message
"Sol Sert" wrote in message
Hi
My digicam generally delivers great pics, BUT like many other cameras it suffers from blue/purple bleed in high contrast areas especially next to highlight. I know, you can buy plugins for PS, but has anybody written a macro, he or she will share?
I’m interested to know how it works, if possible.

Color fringing is caused by an optical defect in the lens design that causes different colors to be refracted differently. The result is that the red, green, and/or blue images are different in size, with red being largest and blue being smallest. Fringing typically shows up in the upper corners of an outdoor image, where the horizon or foliage is silhouetted against the sky.

The quick fix is to use the sponge in desaturate mode to get rid of the unwanted colors, but this is a crude solution at best. A more accurate improvement is can be done by resizing the red and/or blue channels slightly to match the green channel, which is used as a reference.
Here’s a procedure for versions of Photoshop that do not have the Distort>Lens Correction filter. Use the magnifying glass to zoom in on the most extreme area of fringing. Click on the channels, palette, highlight the red channel, click on the "eyecon" for RGB to view the color image, Select All, and select the Edit>Transform tool to minimize the fringing. Repeat for the blue channel.

Magenta/green fringing is fixed by resizing the red channel. To remove any magenta fringe is on the outside of the object, (or green fringe is from the inside) make the red channel smaller. When you are done resizing red you should have either no fringe, or a blue/yellow fringe. If you have a blue yellow fringe, make the blue channel larger as necessary. Use the numeric text fields to enter the zoom setting, since you’ll be working down to the tenths of a percent.

Mike Russell
www.curvemeister.com/forum/

Mike you are so full of useful information
for the longest time I had no clue what channels would or could be used for other than making seps

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