red edge more general?

[ho_co]

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Alan--might be interesting to do with a grey card, but since a grey card bunches the three color channels, I doubt that auto-curves would do anything similar.

 

Thanks for the suggestion, but as I remarked to lct, this is drifting off topic.

 

 

To reiterate: Checking the handling of a new lens, I got a picture. Applying "Curves > Auto" to that picture, I got a result which showed some otherwise hidden color irregularities that resembled some produced by other cameras.

 

I hoped that someone with good technical understanding might be jogged to some idea that could help explain the Italian Flag Syndrome and its relatives.

 

In other words, it was an accidental discovery that I hoped could be helpful.

 

 

It will be interesting to try the camera at different ISOs and on different subjects (e.g. a grey card) and maybe even with different RAW converters. That's of interest to me in exploring why the D200 produced this result, but it's not appropriate to the Leica forum unless it helps explain the M9's red edges.

[AlanG]

Why not try the same thing on scanned images that were shot on film?

[ho_co]

 

Not following your reasoning. How would that relate to Italian Flag Syndrome? Or are you just saying that all digital images show defects?

[Nicoleica]

At the risk of being burned at the stake (Again!), may I throw a potential spanner into the works here by suggesting that the subject itself may be at least partially responsible for the colour shift?

 

A large expanse of sky may have slight colour variations due to the differing thicknesses of atmosphere between various parts of the scene and the angle of the sun.

[mjh]

At the risk of being burned at the stake (Again!), may I throw a potential spanner into the works here by suggesting that the subject itself may be at least partially responsible for the colour shift?

 

A large expanse of sky may have slight colour variations due to the differing thicknesses of atmosphere between various parts of the scene and the angle of the sun.

Yes, some non-uniformity would have to be expected, even in a featureless blue sky, but artefacts aligned with the ultimately arbitrary edges of an image? What natural cause could account for these precisely horizontal or vertical bands?

[ho_co]

Nicole, you're right, of course. I seldom use the D200, but I have shot blue skies before and never noticed this kind of result. Clearly the situation has to do with what's in the picture. Just a 'happy'(?) accident that things happened this way.

 

I'm not so much asking why these results occurred, but why they are so similar to other unexplained phenomena like the "Italian Flag Syndrome" and the M9 "red edges."

 

It's a very narrow question in my mind, and I think Michael has understood it better than I expressed it.

 

I'm delighted for any input because maybe someone will see or say something that sparks a thought that could lead to finding something we're all missing.

 

I've got a similar shot made 3 seconds later that also shows the effect. Could have been the polarizations of the sky, or defects in my sensor reacting with sunspots or cellphone signals, for all I know. Maybe battery level had to do with it, or emanations from the alligator behind me who was wondering why I was shooting the moon when I could have been shooting her. The scene was wispy white clouds, plus the sunshine reflected from the moon, plus the general blue scattering, and a passenger plane mainly silhouetted against all the above.

 

But why the colored streaks running parallel to the frame edges? And why are they similar in color to the other cases I mentioned above?

[jankap]

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The sunlight comes from the right side. Why does the moon have a black skin on the right side?

My opinion is, that the processor in the camera is working for us. Also in the raw-case.

Jan

[AlanG]

I played around with the auto curve feature on two images that were shot on film.

 

The first image below shows the overall image after auto curve was applied.

 

The second image shows what happens when I cropped to only include the sky and then apply auto curve.

 

The second pair shows a sky before auto curve and after.

 

I'd be hesitant to reach any conclusion about a sensor based on what PS auto curve does to sky areas.

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[AlanG]

Another pair - before and after auto curve is applied.

 

It doesn't get the same edge effects as in the D200 image, but the results are pretty weird. Either the D200 image is an anomaly caused by the arrangement of the clouds or there is some aspect of the D200 sensor that causes a bit more pattern when the PS Auto Curve feature works on it. (Whatever it does is certainly based on an algorithm that is not intended for low contrast images that are primarily a single color.)

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[ho_co]

The sunlight comes from the right side. Why does the moon have a black skin on the right side?

Good point, Jan, but I need to disappoint: That line appeared in the JPG conversion and isn't in the RAW. In the second image I made at the same time, for some reason, the conversion to JPG doesn't add that line and makes a much less noticeable light line around the plane.

 

 

But here's an off-the-wall thought:

 

As you said, from the illumination of the moon, one can tell that the canera was pointed into the part of the sky that is 90 degrees from the sun, the ring of maximum polarization. I wonder if the microlenses or the AA filter might contribute a slight polarization for some wavelengths. As far as that goes, I don't know how the particle theory explains polarization, so I might as well wonder whether the edges of the 'photon wells' could contribute some selective polarization.

 

(This theory runs into some trouble as you follow it, but might spark some productive speculation.)

[mjh]

Whatever it does is certainly based on an algorithm that is not intended for low contrast images that are primarily a single color.

It sets the black and white points individually for the three colour channels, spreading the tonal values actually present in the image to use the full range from 0 to 255. The less contrast in the original image, the weirder the results can get as the contrast enhancement can get quite extreme.

[ho_co]

Alan, I like your examples.

 

Looks as if all the astronomers looking for the "green flash" are looking in the wrong place. It's always with us, if we just knew how to look!