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Author Topic: Dynamic range limitations due to glare and flare  (Read 18653 times)

Iliah

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Dynamic range limitations due to glare and flare
« on: July 19, 2015, 04:05:22 pm »

The article discusses a simple experiment allowing to estimate how the camera dynamic range is affected by the glare and flare, and demonstrates that dynamic range figures of 11+ stops may be a bit too optimistic.

http://www.rawdigger.com/Dynamic-range-fair-share-of-flare-and-glare
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Tim Lookingbill

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Re: Dynamic range limitations due to glare and flare
« Reply #1 on: July 19, 2015, 04:13:18 pm »

Are there any real world photographs that show this limited dynamic range due to flare and glare?

That test on that linked article is not how photographers make images especially when editing in a Raw converter to squeeze every bit of DR possible out of a capture.

IOW that article only helps those that take pictures of stars and heavenly bodies at night with a high powered telescope and there isn't a lot of detail in that to begin with unless you're using the Hubble space telescope.
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Iliah

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Re: Dynamic range limitations due to glare and flare
« Reply #2 on: July 19, 2015, 05:10:34 pm »

> Are there any real world photographs that show this limited dynamic range due to flare and glare?

All of them do.
I know some will be disappointed, but truth is the effect is there on any photo. If the scene has 11 stops dynamic range - it is quite visible.
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ErikKaffehr

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Re: Dynamic range limitations due to glare and flare
« Reply #3 on: July 19, 2015, 05:12:22 pm »

+1

Erik


> Are there any real world photographs that show this limited dynamic range due to flare and glare?

All of them do.
I know some will be disappointed, but truth is the effect is there on any photo. If the scene has 11 stops dynamic range - it is quite visible.
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Erik Kaffehr
 

bjanes

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Re: Dynamic range limitations due to glare and flare
« Reply #4 on: July 19, 2015, 05:33:25 pm »

Are there any real world photographs that show this limited dynamic range due to flare and glare?

That test on that linked article is not how photographers make images especially when editing in a Raw converter to squeeze every bit of DR possible out of a capture.

IOW that article only helps those that take pictures of stars and heavenly bodies at night with a high powered telescope and there isn't a lot of detail in that to begin with unless you're using the Hubble space telescope.

The veiling glare and flare light will be overlaid over the luminances of the scene, and contrast will be reduced. The effect will be most marked in the shadows where the flare light will be a significant proportion of the total luminance, but scene luminances will not be destroyed. The effect is similar to viewing a movie with the lights on. Is that correct, Iliah?

I have a well regarded book on photographic exposure dating back to the film era, where the authors stated that flare is not entirely deleterious since it lifts the shadows to a level that can be printed.

Regards,

Bill
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Iliah

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Re: Dynamic range limitations due to glare and flare
« Reply #5 on: July 19, 2015, 05:38:38 pm »

> The veiling glare and flare light will be overlaid over the luminances of the scene, and contrast will be reduced. The effect will be most marked in the shadows where the flare light will be a significant proportion of the total luminance, but scene luminances will not be destroyed. The effect is similar to viewing a movie with the lights on.

Yes, or like projecting the slides with lights on; but that is a part of the story. The other part depends on what we agree to call "scene luminances".

> I have a well regarded book on photographic exposure dating back to the film era, where the authors stated that flare is not entirely deleterious since it lifts the shadows to a level that can be printed.

If it is veiling glare only, and if it is more or less uniform, it is the case sometimes. But even a uniform glare destroys details in shadows.
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Tim Lookingbill

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Re: Dynamic range limitations due to glare and flare
« Reply #6 on: July 19, 2015, 06:38:33 pm »

I agree with the premise of glare and flare limiting DR. I have old film legacy lenses that do this depending on the angle of light to subject and lens.

It's just the article was difficult for me to comprehend as to how they prove this. I thought this article was showing new information I wasn't aware before on this subject and I just didn't see it.

What I've found in practice editing Raw images that have this glare or veil, is it's best to retain but gradually taper off this veil close to black point in order to make out detail like in tree foliage or else wind up with blacks that look like charcoal blotches or holes in the image. Some of these blacks are around 10,10,10RGB and there's nothing else below to apply a curve adjust to taper off into. It's either all black or there's a veil of flare.
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ErikKaffehr

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Re: Dynamic range limitations due to glare and flare
« Reply #7 on: July 19, 2015, 10:07:16 pm »

Hi,

This may be a typical image with a lot of flare, great highlight areas within picture, causing a lot of flare:



This is perhaps an example of a subject with little flare, small windows large dark area. HDR exposure using LumaRiver HDR.



Best regards
Erik
« Last Edit: July 19, 2015, 10:09:50 pm by ErikKaffehr »
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Erik Kaffehr
 

Iliah

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Re: Dynamic range limitations due to glare and flare
« Reply #8 on: July 20, 2015, 09:54:45 am »

Hi Erik,

Indeed, if the light source is present and shadows are empty on the RawDigger histogram, it is due to veiling glare that raises all the levels so that no "true black" is present in raw data.
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Guillermo Luijk

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Re: Dynamic range limitations due to glare and flare
« Reply #9 on: July 20, 2015, 12:43:02 pm »

I am not so sure glare is going to be such a general problem Iliah. The following (tone mapped) scene has more than 16 stops of DR:



Veiling glare is clearly visible in some areas due to lens flare, but in the very dark areas not affected the deep shadows remained deep. I needed a 4 shots / 3 stops apart HDR composite to capture the entire DR. This means my 8 stops Canon 350D could face up to: 8 + (4 - 1) * 3 = 17 stops of real dynamic range. And it did because this was the DR of this scene. This is the linear composite histogram:




And the deep shadows:




The resulting superhdr.tif can be lifted up to 15 stops holding detail:




Other not so radical examples of 12 stops and 11 stops scenes were no problem as well with exposure bracketing:

12 stops: indoor scene (the virtual RAW for download):


RAW histograms:


11 stops: candle flame


Regards






« Last Edit: July 20, 2015, 12:46:41 pm by Guillermo Luijk »
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Iliah

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Re: Dynamic range limitations due to glare and flare
« Reply #10 on: July 20, 2015, 12:48:06 pm »

I am not so sure glare is going to be such a general problem Iliah. The following (tone mapped) scene has more than 16 stops of DR:



Sorry, I can't possibly see this as a generally usable image. On a side note, how did you determine the original scene had 16 EV of range?
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Guillermo Luijk

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Re: Dynamic range limitations due to glare and flare
« Reply #11 on: July 20, 2015, 01:15:04 pm »

How valid the image is results irrelevant, it was just an experiment. The point is that it contained a difference in luminance between its darkest and brightest part of >16 stops. I determined this by looking at the histogram of the linear HDR composite. If it throwed 16 stops of DR it means the real scene was at least of 16 stops, far from the 11 stops limitation you are suggesting. Basically it's a counterexample.

Regards

ErikKaffehr

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Re: Dynamic range limitations due to glare and flare
« Reply #12 on: July 20, 2015, 02:13:29 pm »

Hi,

My take is that something like 0.5% of the light bounces around in the lens and gets on the sensor. A large bright area will have a different effect from a small bright area.

The "concert hall" image I posted is a typical example where flare from windows may play a lesser role.

Best regards
Erik


How valid the image is results irrelevant, it was just an experiment. The point is that it contained a difference in luminance between its darkest and brightest part of >16 stops. I determined this by looking at the histogram of the linear HDR composite. If it throwed 16 stops of DR it means the real scene was at least of 16 stops, far from the 11 stops limitation you are suggesting. Basically it's a counterexample.

Regards

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Erik Kaffehr
 

Iliah

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Re: Dynamic range limitations due to glare and flare
« Reply #13 on: July 20, 2015, 02:32:24 pm »

>The point is that it contained a difference in luminance between its darkest and brightest part of >16 stops

I asked you, "how did you determine the original scene had 16 EV of range?" - that is, what is the map of the spotmeter readings?

Saying the image is not usable I'm not discussing the subject of the image, but the subject of the thread. Not only flare and glare directly, but white balance skews all over "the place".
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Guillermo Luijk

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Re: Dynamic range limitations due to glare and flare
« Reply #14 on: July 20, 2015, 04:43:14 pm »

>The point is that it contained a difference in luminance between its darkest and brightest part of >16 stops

I asked you, "how did you determine the original scene had 16 EV of range?" - that is, what is the map of the spotmeter readings?

Saying the image is not usable I'm not discussing the subject of the image, but the subject of the thread. Not only flare and glare directly, but white balance skews all over "the place".

I didn't care to determine the exact DR of the scene, I just captured it (for which I needed 4 shots 3 stops apart) and the resulting captured data spreaded along 16 stops. That means the original scene had at least 16 stops of DR, well beyond 11.

I didn't use any spotmeter. In fact I didn't meter anything since it is not necessary for HDR capturing. Just a couple of tests are enough and more accurate.

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Iliah

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Re: Dynamic range limitations due to glare and flare
« Reply #15 on: July 20, 2015, 05:48:32 pm »

> the resulting captured data spreaded along 16 stops. That means the original scene had at least 16 stops of DR

Sorry, but no. Nothing substitutes controlled experiments. Those are especially valuable when the image looks wrong.
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AlterEgo

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Re: Dynamic range limitations due to glare and flare
« Reply #16 on: July 20, 2015, 07:08:49 pm »

> the resulting captured data spreaded along 16 stops. That means the original scene had at least 16 stops of DR

Sorry, but no. Nothing substitutes controlled experiments. Those are especially valuable when the image looks wrong.

well, what do you think (subjectively) is the DR of the scene in question and what one can find out from the said 4 raw files (if they are available)... hopefully not something like 8EV vs 16EV claimed ?
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Iliah

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Re: Dynamic range limitations due to glare and flare
« Reply #17 on: July 20, 2015, 07:34:28 pm »

The way it is rendered (without visible details in the window) IMHO it is about 11 stops, give or take.
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Guillermo Luijk

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Re: Dynamic range limitations due to glare and flare
« Reply #18 on: July 21, 2015, 02:29:09 am »

The window has details, even if I could have added some less exposed shot to avoid the little RAW clipping. Don't focus on the particular tone mapping applied (tone mapping captured information that spreads over a range of +16 stops is not an easy task):



I just wanted to show that 11 stops is far from being a limit as imposed by veiling glare.

Regards

Iliah

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Re: Dynamic range limitations due to glare and flare
« Reply #19 on: July 21, 2015, 10:35:46 am »

The window has details, even if I could have added some less exposed shot to avoid the little RAW clipping. Don't focus on the particular tone mapping applied (tone mapping captured information that spreads over a range of +16 stops is not an easy task):



I just wanted to show that 11 stops is far from being a limit as imposed by veiling glare.

Regards

No, it does not contain details. Those are some crude changes in brightness, nothing natural, and the overall contrast is not of a photographic image. Even on your "12 stops: indoor scene" the view from the window in not even close to a natural view. Such HDR is in the forensic processing domain. And again, I would be very interested to see the scene measurements because I think only such measurements may really put a number onto the scenes you are shooting.
« Last Edit: July 21, 2015, 10:41:34 am by Iliah »
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