Best PP technique for magenta / green blotching

[lnikj]

I shot this mackerel sky this morning with my new DP1M.

I note heavy blotches (magenta and green) in the sky and most notably the water. I've seen this on other images too.

What is the best way of dealing with them?

Cheers





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[mike earussi]

In the future always shoot at iso 100 and make sure you're not underexposing.

But in the present the only way I know to at least partially correct the M/G blotches is to mask off and desaturate the offending colors in PS.

 

[lnikj]

I don't know what's happened to the EXIF data on the upload but it was shot at 100. I should have ETTRed though as the (very narrow low contrast) histogram has equal headroom in both directions.

Cheers.

 

[xpatUSA]

Probably OT, but I see some fairly obtrusive compression artifacts in the sky:


Click to see some chessboards and swirly stuff

Just an observation, not saying that they caused the blotching . .

--
Cheers,
Ted

 

[lnikj]

Probably OT, but I see some fairly obtrusive compression artifacts in the sky:


Click to see some chessboards and swirly stuff

Just an observation, not saying that they caused the blotching . .

--
Cheers,
Ted

Just squashed for the upload. Not there in the tiff.

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[Robert F. Tobler]

For large areas with only gentle color transitions (such as the
ocean in your image) you can do the following operation in Photoshop:

1. Convert the Image to Lab color mode

2. use the polygon selection tool or the quick selection tool to select
your area.

3. feather your selection by e.g. 5 to 10 pixels

4. go into the channels panel and only select the a and b channel
(not the L channel)

5. run a gaussian filter with a large kernel of around 50 pixels

Note: This technique requires that there are no sharp color transitions in your
selection.

In your image, this works for the ocean, but not for the sky.

Greetings,

Robert

 

[Kendall Helmstetter Gelner]

Can you post the raw file? I am wondering if SPP noise reduction could be adjusted to better clean that up. The waves have a pretty strong effect for sure.

 

[lnikj]

For large areas with only gentle color transitions (such as the
ocean in your image) you can do the following operation in Photoshop:

1. Convert the Image to Lab color mode

2. use the polygon selection tool or the quick selection tool to select
your area.

3. feather your selection by e.g. 5 to 10 pixels

4. go into the channels panel and only select the a and b channel
(not the L channel)

5. run a gaussian filter with a large kernel of around 50 pixels

Note: This technique requires that there are no sharp color transitions in your
selection.

In your image, this works for the ocean, but not for the sky.

Greetings,

Robert

 

[lnikj]

Here you go: http://lnikj.net/4kendall.X3F

Thanks for taking a look.

 

[khunpapa]

IMHO, all settings are too much. That's why ppl think it's not ISO 100. Even noise reductions are in the extreme ..







--
Flashes of my Memory.

 

[lnikj]

IMHO, all settings are too much. That's why ppl think it's not ISO 100. Even noise reductions are in the extreme ..



--
Flashes of my Memory.

I'm new to SPP so I'm not sure what is going on here. Are those embedded in the file?

Those are not the settings that my OP picture was processed on.

I'm not sure exactly what they were but I'm currently working with a version that looks roughly the same and has these settings:

Exposure, Contrast: .5 Others: 0

Highlight recovery: 1

Auto, Landscape, 5C+7M

Chroma, Luminance, Banding: 3

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[D Cox]

For large areas with only gentle color transitions (such as the
ocean in your image) you can do the following operation in Photoshop:

1. Convert the Image to Lab color mode

2. use the polygon selection tool or the quick selection tool to select
your area.

3. feather your selection by e.g. 5 to 10 pixels

4. go into the channels panel and only select the a and b channel
(not the L channel)

For green/magenta blotches you only need to blur the "a" channel. The "b" channel would deal with blue/yellow blotches.

5. run a gaussian filter with a large kernel of around 50 pixels

You could also reduce the contrast in the "a" channel. (It will be low already, but you can make it lower.)

Note: This technique requires that there are no sharp color transitions in your
selection.

In your image, this works for the ocean, but not for the sky.

Greetings,

Robert

--
Robert F. Tobler
http://rftobler.at/Photography/

 

[khunpapa]

I'm new to SPP so I'm not sure what is going on here. Are those embedded in the file?

Those are not the settings that my OP picture was processed on.

I'm not sure exactly what they were but I'm currently working with a version that looks roughly the same and has these settings:

Exposure, Contrast: .5 Others: 0

Highlight recovery: 1

Auto, Landscape, 5C+7M

Chroma, Luminance, Banding: 3

 

[lnikj]

I'm new to SPP so I'm not sure what is going on here. Are those embedded in the file?

Those are not the settings that my OP picture was processed on.

I'm not sure exactly what they were but I'm currently working with a version that looks roughly the same and has these settings:

Exposure, Contrast: .5 Others: 0

Highlight recovery: 1

Auto, Landscape, 5C+7M

Chroma, Luminance, Banding: 3

 

[maceoQ]

For a Foveon image this is strongly underexposed.
To avoid/reduce color blotches, you have to overexpose in such situations and then pull back the exposure in SPP.

Maceo

 

[manaskarekar]

I think I know what is going on here.

SPP, has a TERRIBLE "feature" that remembers the settings changed for a given photo until you reset it, even when you open a new photo altogether.

I was taken by this a few times myself until I finally figured out what's going on.

There may be a disable option for this somewhere in the preferences.

Hope this helps.

 

[khunpapa]

I think I know what is going on here.

SPP, has a TERRIBLE "feature" that remembers the settings changed for a given photo until you reset it, even when you open a new photo altogether.

I was taken by this a few times myself until I finally figured out what's going on.

There may be a disable option for this somewhere in the preferences.

Hope this helps.

Exactly as you said.
The "disable" is not the option. It's just.here, one click away.



Oh, I so fond of Sigma! Engineer !! <groan>

--
Flashes of my Memory.

 

[PrebenR]

As I cannot delete this post, I'll have a go at the raw file too.

--
Lightwriting with Sigma

 

[Hornbrille]

You could turn down the saturation of green colors. IMHO most cases of color blotches are shadow desaturation artefacts. To avoid color blotches in the shadow you simply desaturate those colors. The effect is the impression of complementary colored blotches. This is the case with your photo. There is almost no magenta in it but it looks like there are magenta blotches. If you inspect the greens (by cranking up the saturation for them) you will immediately see the blotches as desaturation patches in the green carpet. Desaturating greens makes those patches less visible and there is almost no effect on the distant landscape.

Additionally I can achieve best results with Sunlight white balance, no noise reduction and all other sliders at the neutral position.

Uwe

 

[D Cox]

You could turn down the saturation of green colors. IMHO most cases of color blotches are shadow desaturation artefacts. To avoid color blotches in the shadow you simply desaturate those colors. The effect is the impression of complementary colored blotches. This is the case with your photo. There is almost no magenta in it but it looks like there are magenta blotches. If you inspect the greens (by cranking up the saturation for them) you will immediately see the blotches as desaturation patches in the green carpet. Desaturating greens makes those patches less visible and there is almost no effect on the distant landscape.

Additionally I can achieve best results with Sunlight white balance, no noise reduction and all other sliders at the neutral position.

Desaturating green will give the same effect as reducing the contrast of the "a" channel in Lab space, but it is quicker to do.