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FORUMS Post Processing, Marketing & Presenting Photos HDR Creation 
Thread started 01 Apr 2010 (Thursday) 23:37
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'HDR' vs 'tone mapping'

 
_GUI_
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Apr 06, 2010 12:06 |  #16

Shadowblade wrote in post #9941525 (external link)
If you already had all the information in one exposure, you're not actually increasing the image's dynamic range - merely brightening the shadows and dimming the highlights.

If you already had all the information in one exposure, you don't need more exposures, and you can't increase the captured dynamic range because you already have it all. Full stop.

The reason for doing several shots in HDR imaging is because in most high dynamic range situations, with present digital cameras we cannot capture all the information in one exposure: to get non-blown highlights, shadows become too noisy, or to get well exposed shadows, the highlights get clipped. But if we could, just one shot would be fine. For example a HDR camera like the Fuji Super CCD (external link), or the use of a dense GND filter (external link) in a sunset will allow us to capture a high dynamic range in a single shot.

HDR is about capturing all the information (noisefree shadows plus non-clipped highlights) of a high dynamic range scene, and tone mapping it so that it becomes well rendered in the final image. The number of shots needed to achieve it (one, or one million) doesn't play any role in the definition of HDR.

Find here one single RAW file (external link) containing the 12 stops of information of a HDR scene. No more files needed because that single RAW file summarizes (external link) the content of two RAW files shot 4EV apart, that served well to capture all the dynamic range of the real scene. What you can achieve with that single file, is exactly the same to what you could achieve with the original 2 RAW files, no more, no less.

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bsmotril
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Apr 06, 2010 12:56 |  #17

If you start with a RAW file that has recoverable detail in highlights and shadows, and use an HDR processor like Dynamic Photo HDR, then you can get an HDR from a single image. It will not have as large of a dynamic range as a multi exposure based HDR, but it will have more dynamic range than a psuedo tone mapped image from a single exposure. The key is the way the raw file is processed and how good your original exposure was. Shadow Noise certainly becomes a factor though at anything shot much above ISO400.

dugcross wrote in post #9919176 (external link)
I agree with that. The problem is that too many photographers still think their one exposure image is a HDR image. They refuse to listen to anybody and think that just because at the very least they created 2 more images in lightroom or whatever from that single image and took it through Photomatix that the image is HDR when it is not. It is just a tone-mapped image! If you start out with a single image, no matter what you do to it, it will STILL not be a HDR image, it is tone-mapped. Tone-mapping an image does not magically make it HDR.


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Shadowblade
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Apr 06, 2010 20:54 |  #18

bsmotril wrote in post #9943969 (external link)
If you start with a RAW file that has recoverable detail in highlights and shadows, and use an HDR processor like Dynamic Photo HDR, then you can get an HDR from a single image. It will not have as large of a dynamic range as a multi exposure based HDR, but it will have more dynamic range than a psuedo tone mapped image from a single exposure. The key is the way the raw file is processed and how good your original exposure was. Shadow Noise certainly becomes a factor though at anything shot much above ISO400.

There's no such thing as 'recoverable detail'. Detail is either there or it's not - it just may not be apparent in the default tone curves applied in RAW conversion. You can make the detail visible by applying a custom curve to brighten the shadows and darken the highlights - which is essentially what you're doing by using HDR software to combine several conversions of a single RAW file which have been pushed and pulled to different extents, only that you're doing it in another program other than the RAW converter. You haven't changed the image's dynamic range at all, merely the windowing. The extra 'detail' which you're seeing is really a consequence of local contrast enhancement in darker and lighter areas, which, if badly done, can result in 'haloing', as often seen in overblown tone-mapping.




  
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Apr 06, 2010 23:49 |  #19

Shadowblade wrote in post #9946679 (external link)
There's no such thing as 'recoverable detail'. Detail is either there or it's not - it just may not be apparent in the default tone curves applied in RAW conversion. You can make the detail visible by applying a custom curve to brighten the shadows and darken the highlights - which is essentially what you're doing by using HDR software to combine several conversions of a single RAW file which have been pushed and pulled to different extents, only that you're doing it in another program other than the RAW converter. You haven't changed the image's dynamic range at all, merely the windowing. The extra 'detail' which you're seeing is really a consequence of local contrast enhancement in darker and lighter areas, which, if badly done, can result in 'haloing', as often seen in overblown tone-mapping.

Agreed +1


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_GUI_
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Apr 08, 2010 15:22 |  #20

Shadowblade wrote in post #9946679 (external link)
There's no such thing as 'recoverable detail'. Detail is either there or it's not.

In the highlights this is fairly true: you kept the information with maximum detail, or you totally ruined it. We could still talk about partial saturation though (when just one or two of the RAW channels got clipped).

But in the deep shadows of a digital camera, being so taxative (detail is, or it is not) is not correct. When lifting the shadows noise appears, and wheter noise will prevent us to obtain detail from those areas or not will depend on several factors:

  • Scene: if there was detailed texture in the dark areas or not, and how much it was affected by noise
  • Application: the size of the final print copy or resized digital image (noise reduces when downsizing an image)
  • User: how demanding we are about visible noise
For some scene/application/user​, an image could be fine, while for another scene/application/user could have a too low quality.

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Apr 08, 2010 19:36 |  #21

_GUI_ wrote in post #9958323 (external link)
In the highlights this is fairly true: you kept the information with maximum detail, or you totally ruined it. We could still talk about partial saturation though (when just one or two of the RAW channels got clipped).

In which case, creating multiple images would not provide any more detail than adjusting curves (either using the sliders, or manually) during RAW conversion. The detail still isn't recoverable - it's either there (in the non-clipped channels) or not (clipped).

But in the deep shadows of a digital camera, being so taxative (detail is, or it is not) is not correct. When lifting the shadows noise appears, and wheter noise will prevent us to obtain detail from those areas or not will depend on several factors:
  • Scene: if there was detailed texture in the dark areas or not, and how much it was affected by noise
  • Application: the size of the final print copy or resized digital image (noise reduces when downsizing an image)
  • User: how demanding we are about visible noise
For some scene/application/user​, an image could be fine, while for another scene/application/user could have a too low quality.

Regards

That still doesn't make the detail 'recoverable' or 'non-recoverable' - it's either there (above the noise threshold) or not (indistinguishable from noise). The amount of detail visible above the noise threshold may vary, but what is there is there, and what isn't there cannot be recovered, since it isn't there in the first place.




  
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pcr1968
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Apr 09, 2010 05:45 |  #22

I vote not having any info about the shot, and let the experts tell us wich ones are HDR and wich ones are not.


Matthew 11:28-30 :)

  
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Apr 13, 2010 13:42 |  #23

Shadowblade wrote in post #9959728 (external link)
The detail still isn't recoverable - it's either there (in the non-clipped channels) or not (clipped).

I said I agree with your point of clipped vs non-clipped in the highlights.

Shadowblade wrote in post #9959728 (external link)
That still doesn't make the detail 'recoverable' or 'non-recoverable' - it's either there (above the noise threshold) or not (indistinguishable from noise). The amount of detail visible above the noise threshold may vary, but what is there is there, and what isn't there cannot be recovered, since it isn't there in the first place.

I never talked about recovering, just pointed that in the shadows, the border between 'detail is there' and 'detail is not there' is not clear like in the highlights.

For example if you shoot a scene and plan to make a print 2m high, and also publish the image on your site at 800px, for the 2m high print the detail could 'not be there' because the noise was excessive to be able to recognise detailed textures at that size. But the noise reduction when downsizing to 800px for the web could end in an image where the detail 'is there' (of course all the detail you can expect in a 800px image).

In digital sensors, information in the highlights is mostly boolean (we captured it 100%, or we clipped it, no mean term), while information in the shadows is relative (it will depend on several factors such as scene/application/user to consider it valid or not).

pcr1968 wrote in post #9962170 (external link)
I vote not having any info about the shot, and let the experts tell us wich ones are HDR and wich ones are not.

The only way to find out if an image is HDR is to know how much dynamic range the original scene had. To help on this, experience is a must. An indoor room with a window open outside to a sunny day will be HDR, with at least 12 stops of DR. A landscape with no sun in the frame and no strong shadows, will never be HDR.

This IS HDR (not very well tone mapped though, since the floor is more brilliant than the window that produced the reflection):

IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: NOT FOUND | MIME changed to 'image/png'


This is NOT HDR (but it is a specially ugly picture):

IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: NOT FOUND | MIME changed to 'image/png'

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pcr1968
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Apr 14, 2010 05:53 |  #24

_GUI_ wrote in post #9987510 (external link)
I said I agree with your point of clipped vs non-clipped in the highlights.

I never talked about recovering, just pointed that in the shadows, the border between 'detail is there' and 'detail is not there' is not clear like in the highlights.

For example if you shoot a scene and plan to make a print 2m high, and also publish the image on your site at 800px, for the 2m high print the detail could 'not be there' because the noise was excessive to be able to recognise detailed textures at that size. But the noise reduction when downsizing to 800px for the web could end in an image where the detail 'is there' (of course all the detail you can expect in a 800px image).

In digital sensors, information in the highlights is mostly boolean (we captured it 100%, or we clipped it, no mean term), while information in the shadows is relative (it will depend on several factors such as scene/application/user to consider it valid or not).



The only way to find out if an image is HDR is to know how much dynamic range the original scene had. To help on this, experience is a must. An indoor room with a window open outside to a sunny day will be HDR, with at least 12 stops of DR. A landscape with no sun in the frame and no strong shadows, will never be HDR.

This IS HDR (not very well tone mapped though, since the floor is more brilliant than the window that produced the reflection):

IMAGE NOT FOUND
HTTP response: NOT FOUND | MIME changed to 'image/png'


This is NOT HDR (but it is a specially ugly picture):


IMAGE NOT FOUND
HTTP response: NOT FOUND | MIME changed to 'image/png'

Sorry Mate Mine comment was sarcasm, I coudn't care less how many pics people take. If the final result is a nice pic, who cares. I stopped posting to HDR forums due to how much whinging and whining there is. Not just on this site but most other forums as well.


Matthew 11:28-30 :)

  
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'HDR' vs 'tone mapping'
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