HDR

Hi,

I took 7 Cr2 images of the sky with combination of two different f-stops, to get the range 17 stops.
When i assembled them i get blue tint on the final HDR image. What can be the possible reason that i am getting blue color?

···

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Brajesh Lal

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Niels Jernes Vej 14 Aalborg University,
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Hello Brajeshlal(?)

I took 7 Cr2 images of the sky with combination of two different f-stops, to get the range 17 stops.
When i assembled them i get blue tint on the final HDR image. What can be the possible reason that i am getting blue color?

You did not give much detail on what you try to do. What are the sky conditions - do you have the direct sun on you images? What is Cr2? What means blue tint - I would not be surprised if the sky has a blueish color, that is what I observe usually.

Cheers, Lars.

As Lars noted, you need to provide a lot more information for anyone to help you. I know that Cr2 files are the raw output of a Canon camera, but you did not say what program you used to process them, or what options.

-Greg

···

From: [email protected]
Date: June 7, 2010 1:51:36 AM PDT

Hi,

I took 7 Cr2 images of the sky with combination of two different f-stops, to get the range 17 stops.
When i assembled them i get blue tint on the final HDR image. What can be the possible reason that i am getting blue color?

--
Regards,
Brajesh Lal

Hi Lars,

I was referring the paper"Direct HDR Capture of the Sun and Sky" and try to the experiment. Canon Eos 1Ds Mark II with Kodak Wratten ND filter 3.0 is placed in upward direction to capture the sun and sky images. Almost in 50 sec i took 7 raw images ( Canon CR2 format). f4 - 1s, 1/4 and 1/30 and f16 - 1/15, 1/125, 1/1000, 1/8000. Then calculated relative stops between them and used HDRShop 3.0 ( uses directly CR2 format) to assemble it as HDR image.
The image was having bit surroundings and clear sky was and have direct sun.
After assembling it i got the entire HDR image with Blue color tint. I was wondering why i am getting that Blue color tint . Is it camera problem or ND filter or assembling software (HDRShop) or some thing else.

Best Regards, Brajesh Lal

···

________________________________
From: Lars O. Grobe <[email protected]>
To: High Dynamic Range Imaging <[email protected]>
Sent: Mon, June 7, 2010 1:01:29 PM
Subject: Re: [HDRI] HDR

Hello Brajeshlal(?)

I took 7 Cr2 images of the sky with combination of two different f-stops, to get the range 17 stops.
When i assembled them i get blue tint on the final HDR image. What can be the possible reason that i am getting blue color?

You did not give much detail on what you try to do. What are the sky conditions - do you have the direct sun on you images? What is Cr2? What means blue tint - I would not be surprised if the sky has a blueish color, that is what I observe usually.

Cheers, Lars.

This is probably due to the handling of clipped values in the Canon raw files in HDRshop, but I can't say for sure as I don't have experience with this program. You could try assembling the images in Photoshop (CS3 or higher) to see what happens.

FYI, this list deals mostly with Mac users of Photosphere and related tools, so I don't think you'll find many experts on HDRshop, but I could be wrong.

Best,
-Greg

···

From: Brajesh Lal <[email protected]>
Date: June 7, 2010 4:22:28 AM PDT

Hi Lars,

I was referring the paper "Direct HDR Capture of the Sun and Sky" and try to the experiment. Canon Eos 1Ds Mark II with Kodak Wratten ND filter 3.0 is placed in upward direction to capture the sun and sky images. Almost in 50 sec i took 7 raw images ( Canon CR2 format). f4 - 1s, 1/4 and 1/30 and f16 - 1/15, 1/125, 1/1000, 1/8000. Then calculated relative stops between them and used HDRShop 3.0 ( uses directly CR2 format) to assemble it as HDR image.
The image was having bit surroundings and clear sky was and have direct sun.
After assembling it i got the entire HDR image with Blue color tint. I was wondering why i am getting that Blue color tint . Is it camera problem or ND filter or assembling software (HDRShop) or some thing else.

Best Regards, Brajesh Lal

From: Lars O. Grobe <[email protected]>
To: High Dynamic Range Imaging <[email protected]>

Hello Brajeshlal(?)

> I took 7 Cr2 images of the sky with combination of two different f-stops, to get the range 17 stops.
> When i assembled them i get blue tint on the final HDR image. What can be the possible reason that i am getting blue color?

You did not give much detail on what you try to do. What are the sky conditions - do you have the direct sun on you images? What is Cr2? What means blue tint - I would not be surprised if the sky has a blueish color, that is what I observe usually.

Cheers, Lars.

Hi!

placed in upward direction to capture the sun and sky images. Almost in 50
sec i took 7 raw images ( Canon CR2 format). f4 - 1s, 1/4 and 1/30 and f16
- 1/15, 1/125, 1/1000, 1/8000. Then calculated relative stops between them
and used HDRShop 3.0 ( uses directly CR2 format) to assemble it as HDR
image.

I do not know the internals of how this raw format is handled. One thing that comes to my mind is that getting a relieable response curve for the camera over the whole luminance range and for all three channels may be challenging. I do not know what you use to derive the response of the sensor from. If it is a typical greyish indoor scene, you probably cannot do it with the filter in place. If you use the real sunny sky for calculating the sensor response, the different channels may perform different for the direct sun. Just a guess though.

Did you try other software, and did this result in the same blue tint?

Cheers, Lars.

Hullo again,

I would like to move this off-list because I do realise that all these
questions about HDRI are only of peripheral interest to the RADIANCE
community at large. However, a quick Google tought me that the majority of
HDR discussion seem to be going on at
http://www.hyperfocaldesign.com/,
and frankly, it doesn't seem to cut the custard for me. So please DO tell
me if there is a more appropriate List to direct this one to...

And 'ere we go:

I've just put up a few more examples on the WebHDR Gallery page, and
noticed that all of the tonemapped images are rather desaturated, compared
to what you get when hitting the old 'Do-it-all-for-me-Button' in Auto
Mode. I understand that most if not all digital consumer cameras do some
jigger-pokery colour gamut stretching, so the photos look a bit nicer.
However, my understanding is that once you've done an HDR, you can do all
sorts of things to it, probablay including those colour transform
things...

Since I am processing all results of WebHDR with RADIANCE tools, I was
wondering if there is a way of putting the colour-vibrancy back into the
tone mapped imaged.

Cheers

Axel

Hi Axel,

It seems to me that HDRI is quite relevant to this community, as there are a variety of people interested in the topic. Perhaps we should ask:

   1. is this topic appropriate for this particular radiance list
      (radiance-general)
   2. if not would it be worth it to set up a
      [email protected]

-Jack

Axel Jacobs wrote:

···

Hullo again,

I would like to move this off-list because I do realise that all these
questions about HDRI are only of peripheral interest to the RADIANCE
community at large. However, a quick Google tought me that the majority of
HDR discussion seem to be going on at
http://www.hyperfocaldesign.com/,
and frankly, it doesn't seem to cut the custard for me. So please DO tell
me if there is a more appropriate List to direct this one to...

And 'ere we go:

I've just put up a few more examples on the WebHDR Gallery page, and
noticed that all of the tonemapped images are rather desaturated, compared
to what you get when hitting the old 'Do-it-all-for-me-Button' in Auto
Mode. I understand that most if not all digital consumer cameras do some
jigger-pokery colour gamut stretching, so the photos look a bit nicer.
However, my understanding is that once you've done an HDR, you can do all
sorts of things to it, probablay including those colour transform
things...

Since I am processing all results of WebHDR with RADIANCE tools, I was
wondering if there is a way of putting the colour-vibrancy back into the
tone mapped imaged.

Cheers

Axel

_______________________________________________
Radiance-general mailing list
[email protected]
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--
# Jack de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction

Hi Jack, Axel,

I agree that a separate HDRI mailing list makes sense, if Peter A-B is willing to set one up. I would certainly participate, and it would save those who may not be interested from our noise.

Regarding color in HDR images, this really falls under the category of tone-mapping. Most film and digital cameras increase color saturation according to well-worn practices, which may be found in R.W.G. Hunt's classic tome on color management, "The Reproduction of Colour" (ISBN 0-470-02425-9). Unfortunately, few tone-mapping algorithms actually pay much attention to preference with respect to color, and I know of at least two reasons why not:

1) People prefer increased gamma or saturation on their colors, which happens to correspond to less dynamic range in the reproduction -- in other words, boosting saturation makes it difficult to represent your larger luminance range.

2) Increasing saturation, or even leaving it alone, while compressing an image's dynamic range makes colors look *too* saturated in many images, because a loss in contrast is often read as haze by the human visual system, and your brain compensates by imagining the colors to be more saturated than they appear.

That said, you can of course play around with the gamma when you convert to 24-bit/pixel formats, and get a boost in contrast and saturation that way. Sometimes the results will be nicer, oftentimes they will be worse. To boost contrast/saturation, try:

  pcond capture.hdr | ra_tiff -g 1.6 - boosted.tif

To reduce contrast/saturation try:

  pcond capture.hdr | ra_tiff -g 2.7 - reduced.tif

There are more sophisticated ways to play around with contrast and saturation separately using pcomb, but I'm not sure you gain that much by them.

-Greg

···

From: Jack de Valpine <[email protected]>
Date: January 16, 2006 7:53:24 AM PST

Hi Axel,

It seems to me that HDRI is quite relevant to this community, as there are a variety of people interested in the topic. Perhaps we should ask:
is this topic appropriate for this particular radiance list (radiance-general)
if not would it be worth it to set up a [email protected]
-Jack

--------------------

From: "Axel Jacobs" <[email protected]>
Date: January 15, 2006 8:26:53 PM PST

Hullo again,

I would like to move this off-list because I do realise that all these
questions about HDRI are only of peripheral interest to the RADIANCE
community at large. However, a quick Google tought me that the majority of
HDR discussion seem to be going on at
http://www.hyperfocaldesign.com/,
and frankly, it doesn't seem to cut the custard for me. So please DO tell
me if there is a more appropriate List to direct this one to...

And 'ere we go:

I've just put up a few more examples on the WebHDR Gallery page, and
noticed that all of the tonemapped images are rather desaturated, compared
to what you get when hitting the old 'Do-it-all-for-me-Button' in Auto
Mode. I understand that most if not all digital consumer cameras do some
jigger-pokery colour gamut stretching, so the photos look a bit nicer.
However, my understanding is that once you've done an HDR, you can do all
sorts of things to it, probablay including those colour transform
things...

Since I am processing all results of WebHDR with RADIANCE tools, I was
wondering if there is a way of putting the colour-vibrancy back into the
tone mapped imaged.

Cheers

Axel

IMHO, HDRI may or may not require the color reproduction and saturation to be as accurate or appealing. IIt seems to me that, in general, saturation and color issues are less important when using a HDRI for image-based lighting than when using the technique of converting a sequence of LDRI to a single HDRI for increased dynamic range in a tone-mapped photograph, where the final output will be an image of the scene as opposed to a light probe image for IBL.

Could hdrgen/Photosphere possibly benefit from more control over tone-mapping in a way similar to the CameraRaw presents options for exposing a RAW image? If the use of HDRI for general photography (which I am really getting interested in, BTW) would other users find it useful to expand the ability of hdrgen/Photosphere to present the user more control over the tone mapping process? This kind of discussion could probably fill a whole new forum, and I would be all for it, if it is not too much of a hassle.

Interesting as always!

kirk

···

------------------------------

Kirk L. Thibault, Ph.D.
[email protected]

p. 215.271.7720
f. 215.271.7740
c. 267.918.6908

skype. kirkthibault

On Jan 16, 2006, at 11:14 AM, Greg Ward wrote:

Hi Jack, Axel,

I agree that a separate HDRI mailing list makes sense, if Peter A-B is willing to set one up. I would certainly participate, and it would save those who may not be interested from our noise.

Hi Kirk,

Peter is quick. He has just set up a new mailing list, [email protected], which I suggest you subscribe to and we will move the discussion there.

HDRI generation is a separate issue from tone-mapping, and although Photosphere attempts to do both, it only makes a weak effort in the tone-mapping department. Hdrgen makes no effort to tone-map images, and it should not. In fact, I don't recommend tone-mapping HDR images into HDR, but directly into the destination display's color space, as an HDR image should maintain it's scene-referred color space. Some of these issues are discussed and spelled out on hdrsoft's excellent FAQ page:

  http://www.hdrsoft.com/resources/dri.html

Since you bring up RAW (also discussed by hdrsoft), I should mention that although it is tempting to shoot RAW in preparation for creating HDR images, I have found it not to be helpful in most cases. The additional range/resolution obtained is modest, and the confusion resulting from the many "development" options you mention means that reproducibility is an issue. Unless you have a method to go straight from RAW into HDRI, you are better off shooting high-quality JPEGs on most cameras.

I'll make an announcement under a new topic about the HDRI mailing list, and let's continue the discussion there.

-Greg

···

From: Kirk Thibault <[email protected]>
Date: January 16, 2006 8:49:46 AM PST

IMHO, HDRI may or may not require the color reproduction and saturation to be as accurate or appealing. IIt seems to me that, in general, saturation and color issues are less important when using a HDRI for image-based lighting than when using the technique of converting a sequence of LDRI to a single HDRI for increased dynamic range in a tone-mapped photograph, where the final output will be an image of the scene as opposed to a light probe image for IBL.

Could hdrgen/Photosphere possibly benefit from more control over tone-mapping in a way similar to the CameraRaw presents options for exposing a RAW image? If the use of HDRI for general photography (which I am really getting interested in, BTW) would other users find it useful to expand the ability of hdrgen/Photosphere to present the user more control over the tone mapping process? This kind of discussion could probably fill a whole new forum, and I would be all for it, if it is not too much of a hassle.

Interesting as always!

kirk

Peter and Greg - you guys rock.

Thanks!

···

------------------------------

Kirk L. Thibault, Ph.D.
[email protected]

p. 215.271.7720
f. 215.271.7740
c. 267.918.6908

skype. kirkthibault

On Jan 16, 2006, at 12:37 PM, Gregory J. Ward wrote:

Hi Kirk,

Peter is quick. He has just set up a new mailing list, [email protected], which I suggest you subscribe to and we will move the discussion there.

HDRI generation is a separate issue from tone-mapping, and although Photosphere attempts to do both, it only makes a weak effort in the tone-mapping department. Hdrgen makes no effort to tone-map images, and it should not. In fact, I don't recommend tone-mapping HDR images into HDR, but directly into the destination display's color space, as an HDR image should maintain it's scene-referred color space. Some of these issues are discussed and spelled out on hdrsoft's excellent FAQ page:

  http://www.hdrsoft.com/resources/dri.html

Since you bring up RAW (also discussed by hdrsoft), I should mention that although it is tempting to shoot RAW in preparation for creating HDR images, I have found it not to be helpful in most cases. The additional range/resolution obtained is modest, and the confusion resulting from the many "development" options you mention means that reproducibility is an issue. Unless you have a method to go straight from RAW into HDRI, you are better off shooting high-quality JPEGs on most cameras.

I'll make an announcement under a new topic about the HDRI mailing list, and let's continue the discussion there.

-Greg

From: Kirk Thibault <[email protected]>
Date: January 16, 2006 8:49:46 AM PST

IMHO, HDRI may or may not require the color reproduction and saturation to be as accurate or appealing. IIt seems to me that, in general, saturation and color issues are less important when using a HDRI for image-based lighting than when using the technique of converting a sequence of LDRI to a single HDRI for increased dynamic range in a tone-mapped photograph, where the final output will be an image of the scene as opposed to a light probe image for IBL.

Could hdrgen/Photosphere possibly benefit from more control over tone-mapping in a way similar to the CameraRaw presents options for exposing a RAW image? If the use of HDRI for general photography (which I am really getting interested in, BTW) would other users find it useful to expand the ability of hdrgen/Photosphere to present the user more control over the tone mapping process? This kind of discussion could probably fill a whole new forum, and I would be all for it, if it is not too much of a hassle.

Interesting as always!

kirk

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Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general