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Author Topic: Better than ETTR ?  (Read 18980 times)
bjanes
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« Reply #100 on: August 21, 2011, 09:11:14 AM »
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Interesting! An excellent demonstration of the situation, Guillermo. Thanks. It makes sense that the red channel would be the last to be clipped in a blue sky, unless it were a sunrise or sunset.

I guess someone at Adobe has decided that a reconstruction of a blown sky that leans towards cyan is more acceptable than one which leans towards magenta.

Ray,

The Adobe software may not be as intelligent as you think. Rather than identifying a blown sky, ACR may have merely identified a clipped area. When reconstructing blown areas, ACR pushes blown areas to neutral. The red channel is the only one intact in the photo, so ACR may have added blue and green, resulting in a cyan cast.

DCRaw has various highlight recovery options. See Guillermo's post on highlight recovery and look at the reconstructions of blown facial highlights in his example. ACR pushes them towards white, whereas DCRaw looks at the adjacent colors in determining the reconstruction.

ETTR is a good thing, but when one pushes it to extreme, clipping and data loss will occur. The prudent photographer avoids data loss rather than depending on implementation of highlight recovery in software. With today's high performance sensors, a bit of underexposure can be tolerated if bracketing is not feasible. Since blown highlights are often relatively neutral in color cast, highlight recovery can often rescue inadvertently overexposed images. However, I think that successful reconstruction has more to do with the SNR than the abundance of levels in the highlights as claimed by some experts. Shot noise and rendering of the raw file will usually be sufficient to dither the image and prevent banding.

Regards,

Bill
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ejmartin
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« Reply #101 on: August 21, 2011, 05:43:54 PM »
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I've generally found ACR to be either better than other converters at recovering highlights, or at least as good, whenever I've taken the trouble to make a comparison.

Making more extreme adjustments to my previous example, it seems clear that the blue sky is definitely blown out to a degree which ACR cannot rectify. However, I doubt that any other converter could do a more convincing job of reconstructing that lost data.

May I have the raw file to play with?

Here is an example that works particularly well with RawTherapee's (in the dev version, 4.0) recently revamped color propagation method of highlight recovery:

« Last Edit: August 21, 2011, 06:12:53 PM by ejmartin » Logged

emil
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« Reply #102 on: August 21, 2011, 06:07:47 PM »
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Hi Ray,

It might teach a valuabe lesson (without having to repeat it for every file), e.g. that Highlight Recovery should only be used after an adjustment of the exposure (and perhaps the brightness) slider(s). When Rawnalyse tells you that there are no clipped highlights, then why use the HR tool?

Cheers,
Bart

It depends how ACR does HR.  The raw file may have no clipped highlights, but WB can send some channels past the white point.  A good HR tool should be able to distinguish channels that are clipped because of WB vs those that are clipped because the raw data is clipped.
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emil
BartvanderWolf
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« Reply #103 on: August 21, 2011, 06:28:52 PM »
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It depends how ACR does HR.  The raw file may have no clipped highlights, but WB can send some channels past the white point.

Hi Emil,

A good point, althought the potentially best method to avoid data clipping due to WB would be a bit more -EV correction at the Raw conversion stage.

Quote
 A good HR tool should be able to distinguish channels that are clipped because of WB vs those that are clipped because the raw data is clipped.

Exactly, fully agree with that.

Cheers,
Bart
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ejmartin
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« Reply #104 on: August 21, 2011, 07:27:44 PM »
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Hi Emil,

A good point, althought the potentially best method to avoid data clipping due to WB would be a bit more -EV correction at the Raw conversion stage.

The tricky bit is that -EV correction to save unclipped channels runs the risk of messing up clipped channels, bringing them down into the visible range, with disastrous hue shifts.
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emil
Ray
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« Reply #105 on: August 21, 2011, 08:34:08 PM »
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May I have the raw file to play with?

Here is an example that works particularly well with RawTherapee's (in the dev version, 4.0) recently revamped color propagation method of highlight recovery:


Hi Emil,
I've sent you the RAW image as requested plus another one with an even greater degree of blown sky, as detailed below.

Thanks for your interest.

Regards,   Ray
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ejmartin
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« Reply #106 on: August 21, 2011, 09:17:40 PM »
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Here's RawTherapee on the first one.  The Color Propagation recovery tool is still experimental -- I had to adjust the pre-demosaic CA correction manually to keep the CA in the image from infecting the highlight recovery.  I'll have to fix that in the next iteration.  The blown area is still a little too pink for my taste.

The second image is too blown to recovery anything in the sky -- there is no unblown region to inpaint from.

« Last Edit: August 21, 2011, 09:25:48 PM by ejmartin » Logged

emil
Ray
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« Reply #107 on: August 21, 2011, 10:09:26 PM »
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Here's RawTherapee on the first one.  The Color Propagation recovery tool is still experimental -- I had to adjust the pre-demosaic CA correction manually to keep the CA in the image from infecting the highlight recovery.  I'll have to fix that in the next iteration.  The blown area is still a little too pink for my taste.

The second image is too blown to recovery anything in the sky -- there is no unblown region to inpaint from.



Hi Emil,

That's amazing! Are you involved in the development of RAW Therapee? Version 4 looks as though it could be very useful. I look forward to using it.

Cheers!   Ray
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ejmartin
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« Reply #108 on: August 21, 2011, 10:17:57 PM »
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Hi Emil,

That's amazing! Are you involved in the development of RAW Therapee? Version 4 looks as though it could be very useful. I look forward to using it.


Yes, I started revamping the image processing pipeline when it went open source a little over a year ago.  We're slowly getting our act together...
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emil
ErikKaffehr
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« Reply #109 on: August 22, 2011, 02:49:41 AM »
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Hi,

Very much impressed...

Best regards
Erik

Yes, I started revamping the image processing pipeline when it went open source a little over a year ago.  We're slowly getting our act together...
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Guillermo Luijk
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« Reply #110 on: August 22, 2011, 10:46:58 AM »
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Impressive!
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