Best PP technique for magenta / green blotching

Started Mar 5, 2014 | Discussions
lnikj Regular Member • Posts: 190
Best PP technique for magenta / green blotching
3

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 Veteran Member • Posts: 8,932
Re: Best PP technique for magenta / green blotching

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.

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OP lnikj Regular Member • Posts: 190
Re: Best PP technique for magenta / green blotching

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.

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xpatUSA
xpatUSA Forum Pro • Posts: 18,585
Re: Best PP technique for magenta / green blotching

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 . .

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Cheers,
Ted

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OP lnikj Regular Member • Posts: 190
Re: Best PP technique for magenta / green blotching

xpatUSA wrote:

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 . .

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

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Robert F. Tobler
Robert F. Tobler Senior Member • Posts: 1,149
A Photoshop technique for some cases...

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

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MOD Kendall Helmstetter Gelner Forum Pro • Posts: 20,587
Re: Best PP technique for magenta / green blotching

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.

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OP lnikj Regular Member • Posts: 190
Re: A Photoshop technique for some cases...

Robert F. Tobler wrote:

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

That's a great use of LAB I have never come across before. Good technique. Working with the tiff that has cleaned up the ocean, even better when run twice.

Cheers.

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OP lnikj Regular Member • Posts: 190
Re: Best PP technique for magenta / green blotching

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

Thanks for taking a look.

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khunpapa
khunpapa Senior Member • Posts: 2,664
Re: Best PP technique for magenta / green blotching

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

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OP lnikj Regular Member • Posts: 190
Re: Best PP technique for magenta / green blotching

khunpapa wrote:

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

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 Forum Pro • Posts: 27,899
Re: A Photoshop technique for some cases...

Robert F. Tobler wrote:

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

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khunpapa
khunpapa Senior Member • Posts: 2,664
Re: Best PP technique for magenta / green blotching

lnikj wrote:

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

As my SPP is set to "zero everything", when I open your file - everything vastly differ from your pic in this topic.
I have to change all the settings above to get this close result.
I think you should reset all settings to zero value, included that highlight recovery. WB should be Sunlight, or auto
SPP is very far, far away from being "good raw editing software" I suggest you should change onlysome Foveon-specific settings in SPP, the export it as TIFF to another decent PP software.
Mostly, I use only WB and Color AdjustmentHighlight Correction always 0, Sharpness -1.
Noise Reduction in the middle or lowest, except when there's obvious Banding Noise.
Let's fun

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OP lnikj Regular Member • Posts: 190
Re: Best PP technique for magenta / green blotching

khunpapa wrote:

lnikj wrote:

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

As my SPP is set to "zero everything", when I open your file - everything vastly differ from your pic in this topic.
I have to change all the settings above to get this close result.
I think you should reset all settings to zero value, included that highlight recovery. WB should be Sunlight, or auto
SPP is very far, far away from being "good raw editing software" I suggest you should change onlysome Foveon-specific settings in SPP, the export it as TIFF to another decent PP software.
Mostly, I use only WB and Color Adjustment. Highlight Correction always 0, Sharpness -1.
Noise Reduction in the middle or lowest, except when there's obvious Banding Noise.
Let's fun

I have no idea why that is happening but as I said I am new to SPP. Info on the file I uploaded gives me:

File Name: 4kendall.X3F

File Type: X3F

Image Dimensions: 44.3 MP (4704 x 3136 x 3)

File Size: 46.54 MB

Location: /Users/nik/Downloads

Capture Date: 5/4/14 07:34:10

Exposure Mode: A - Aperture Priority AE

Exposure Compensation: 0

ISO Setting: 100

White Balance Setting: Auto

Color Mode: Vivid (ex-Standerd)

Flash: Off

Shutter Speed: 1/125

Aperture Value: F7.1

Metering Mode: Evaluative Metering

Focus Setting: AF-S - Single Auto Mode

Focal Length: 19 mm

Resolution: HI

Drive Mode: Self-Timer

Camera: SIGMA DP1 Merrill

Firmware Version: 1.04.3.7091

image Unique ID: 3030333038373134F2B13F5333434443

X3F Settings

Exposure: +0.0

Contrast: +0.0

Shadow: +0.0

Highlight: +0.0

Saturation: +0.0

Sharpness: +0.0

X3 Fill Light: +0.0

Color Adjustment: 0

Chroma NR: 1.00

Luminance NR: 0.00

So it doesn't look like I accidentally saved anything back to the file.

Thanks for your recommendations.

Cheers.

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(unknown member) Senior Member • Posts: 1,857
exposure
3

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 Regular Member • Posts: 201
Re: Best PP technique for magenta / green blotching

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.

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khunpapa
khunpapa Senior Member • Posts: 2,664
Re: Best PP technique for magenta / green blotching

manaskarekar wrote:

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>

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PrebenR Veteran Member • Posts: 4,164
Re: Best PP technique for magenta / green blotching

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

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Hornbrille
Hornbrille Regular Member • Posts: 371
Re: Best PP technique for magenta / green blotching

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 8-)

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D Cox Forum Pro • Posts: 27,899
Re: Best PP technique for magenta / green blotching

Hornbrille wrote:

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.

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