Purple artifacts in water drops

[Alberti]

When I was shooting in the mountains last week I had several occasions that the water showed artifacts - purple fringes.
This does not disappear when sliding the Phase One Highlight nor does it change with reduced exposure.
The whites within the drops are overexposed - white in the center.
> Is it physical (a small diffraction effect, 'rainbow')?
> Is it electronic (a DNG effect)?

To test the latter, I ran the raw file through the Adobe DNG converter, and though this improived the overall attitude of the picture, this artifact in fact worsened.
> This can be due to the somewhate 'Holmes-Chrome character the converted file has.
> note that with Adobe DNG converter, the details have much improved!!!

Is there anyway to remedy this? Or how should I prevent this? (I did not use my IR filter!)
Hope someone can shed some light on this.
(apologies for the subject matter; I make such small stone 'men' in the mountain brooks just for fun).
Alberti

[stunsworth]

It's normal, and the filter doesn't remove it - it's not an IR artefact. I'm sure someone with more technical knowledge than me can explain the cause of the issue.

[Jamie Roberts]

According to a Canon tech I spoke to years ago on this, it's called birefringence and happens at the sensor level; it's a type of chromatic abberation. It happens when you have severly overexposed areas of the image and is an interaction between lens design and sensor.

In my experience, Leica lenses cause this way less often than others.

There is a great, and cheap, PS plugin that cleans this up quickly and easily... it's $10 and worth every penny:

Color Fringe Reducer 5.0 - Shay Stephens Photography

Note that there's a GIMP Linux version and PaintShop version available now too!

FWIW--DxO optics also corrects this, IIRC.

[Alberti]

Originally Posted by Jamie Roberts

There is a great, and cheap, PS plugin that cleans this up quickly and easily... it's $10 and worth every penny:

Color Fringe Reducer 5.0 - Shay Stephens Photography

Note that there's a GIMP Linux version and PaintShop version available now too!

FWIW--DxO optics also corrects this, IIRC.

Jamie,
Thanks a lot for this information; unfortunately I do not have Photoshop (this on my whishlist for next year) so this plugin can't help me now.
regards
alberti

[adan]

First, purple edges to bright highlights happens with digital. (BTW I get purple tints to water drops fairly often, too). There are several things that can produce it and they can all occur in the same image, reinforcing one another.

They are a) blooming of overexposure into surrounding pixels, b) aliasing artifacts where the fine drops of water fall mostly on a red or blue pixel, c) chromatic aberrations (CA) in the sensor glass/microlenses, and d) CA in the taking lens.

The 50 'cron is very low in CA, so that can be ignored. The fact the M8 uses no anti-aliasing filter can increase the effect of (b). Making sure the exposure is biased for the highlights (underexposure) can cut back blooming.

Otherwise - increasing the amount of COLOR noise reduction can smooth out and diffuse the strong purples and make them much weaker (or even vanish. Also going into the Hue/Saturation/Brightness control in whatever image software you use and selectively decreasing the magenta and blue saturation for those areas where the problem is visible can often make it invisible.

Here is your 4th image using that last technique - reduction of the magenta saturation and a Hue shift towards red to blend it into the brown stones and river bottom.

If the background had been blue, I'd have shifted the magenta towards blue; if the background were green, I'd have used color noise reduction to spread the magenta into the green (neutralizing it with complementary color).

Finally, I do find that using an IR filter REDUCES this effect somewhat. The M8 will always overemphasize magentas and reds - whatever their source - unless the influence of IR is cut off. Shooting color on the M8 without an IR filter is always a crapshoot with the dice loaded against you.

[Alberti]

Originally Posted by adan

Here is your 4th image using that last technique - reduction of the magenta saturation and a Hue shift towards red to blend it into the brown stones and river bottom.

Shooting color on the M8 without an IR filter is always a crapshoot with the dice loaded against you.

Thanks Adan,
very convincing output (though somewhat troublesome number of steps in this workflow).
--> I did indeed overexpose some pictures, due to the harsh environment.

Now, looking at the effect you made, I see that the posting nr 3 does not show up all that much magenta fringe at all. On the PhaseOne 'development' screen and on the Windows preview of the generated JPEG there is much more! The posting took away some too! Maybe an effect of the suurounding light at night in my workroom.
And I note too (also going back to the JPEGS) that the Adobe Converter produces more purple than the Phase One conversion, even though I did select manually the Leica generic profile (this tag was 'lost' in the conversion.)
alberti

[rickp13]

hello
i reported the same problem in an earlier thread, and ended up using the shay stephens plug-in to correct it (easily, inexpensively!!). i know you don't have photoshop yet, but here, just FYI, are the before and after photos using the plug-in.

good luck

rick

[jaapv]

Using C1 instead of Lightroom or ACR will reduce the problem somewhat. If all else fails, there is still a black-and white conversion

[Jamie Roberts]

Originally Posted by Alberti

Jamie,
Thanks a lot for this information; unfortunately I do not have Photoshop (this on my whishlist for next year) so this plugin can't help me now.
regards
alberti

Alberti,

It looks like you don't need to have Photoshop any longer; Shay wrote a script for the GIMP editor. GIMP is an open source (free to use) image editor.

Look here:

Color Fringe Reducer 5.0 for the GIMP - Shay Stephens Photography

Still $10...

[Alberti]

Originally Posted by Jamie Roberts

Alberti,

It looks like you don't need to have Photoshop any longer; Shay wrote a script for the GIMP editor. GIMP is an open source (free to use) image editor.

Look here:

Color Fringe Reducer 5.0 for the GIMP - Shay Stephens Photography

Still $10...

Jamie - You are a great salesman.
Just went into the buying mode!
Alberti

[Jamie Roberts]

Well, I hope it works for you! Let us know!!