Purple fringe?

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

Sol Sert

Re: Purple fringe?

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
the boxing cat site is very cute!!
have seen that vid before...but never such a huge collection

KatWoman

Re: Purple fringe?

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/

Mike Russell

Re: Purple fringe?

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.

Sol Sert

Re: Purple fringe?

...
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 Russell

Re: Purple fringe?

Using PS 7 (Danish), alas!
Naturally I have searched The Net, but to no avail...

Sol Sert

Re: Purple fringe?

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.