[HDR-photo] xmp files

Tue Dec 12 23:16:26 EST 2006

On 12/10/06, Ferrell McCollough <ferrellmc at comcast.net> wrote:
>
>  Hello,
>
> I think xmp files for HDR images would be a benefit to the user.
> Although PM includes in the file name the number of images and the
> starting file, for example Set01HDRI5from_DSC2535.hdr,  it doesn't help us
> if we have 5 bracketed images and only use 2 or 3 of the set.  An xmp
> file should list the file name w/ extension, image size, exposure values,
> and EV steps.
>
> Some cameras, like Nikon have a max 1EV step when using AEB mode, so in
> order to use AEB and get a +2EV and a -2EV sequence we need to shoot 5
> images and delete or not include the +/-1EV images in the merging. I've
> notified Nikon of the need for AEB of 5frames @ 2EV steps. Hopefully it's
> just a firmware update. Other camera's like Pentax, Fuji and Olympus only
> allow 3 frames at a max of 1EV step (except for the Fuji S3 Pro which allows
> 2EV steps)   Ferrell, the Pentax K10D can go up to 2 full stops, btw.
>
> Here's a typical Nikon AEB shoot sequence:
> 5 images @ 1EV step:
>
> 5385.nef    0EV
> 5386.nef    -2EV
> 5387.nef    -1EV
> 5388.nef    +1EV
> 5389.nef    +2EV
>
>  If I used 3 images of this 5 image set I'd like to know in the xmp file
> if it was the 0EV, +1EV, -1EV, or the 0EV, +2EV, -2EV for example. Using all
> 5 images isn't necessary.
>
> Here is an example of xmp info in which the +/-2EV steps were used. It
> includes the file names, sizes, exp and EV step.
>
>  DSC5385.NEF    4320x2868    1/50sec - F/18    +/-0EV
> DSC5386.NEF    4320x2868    1/200sec - F/18    -2EV
> DSC5389.NEF    4320x2868    1/13sec - F/18    +2EV
>
>
> Canon on the other hand is able to shoot 3 frames @ 2EV steps in AEB
> mode. For a high contrast scene in which +/-4EV is needed, the photographer
> can dial in -2EV then shoot AEB for a sequence of -4EV, -2EV, 0EV. Then dial
> in +2EV and shoot another AEB set for a sequence of +4EV, +2EV, 0EV. The end
> result is a very high dynamic range capture but there are two images that
> are 0EV. One must be deleted or not used in the merging. It would be nice to
> know, especially in ghost analysis, which 0EV was used.
>
> So as you can see present camera technology is designed for small
> incremental bracketing or limited bracketing. This is good for choosing the
> best single shot of the scene but not for HDR merging. So as we shoot we
> capture more images than we need, some get deleted, and some become part of
> the merging. An xmp file will show us which ones were part of the merging.
>
> Shooting in AEB mode is the superior method as it doesn't require touching
> the camera between images. The less you touch the camera the less the chance
> of camera movement. Also AEB allows for continuous shooting at high fps.
>  Shooting in manual, or using exposure compensation requires dialing-in each
> exposure and unless the camera is tethered there is a chance of movement
> even if on a pixel level. Shooting in manual also has a slight disadvantage
> of not including EVsteps in the Raw xmp file, just f-stop and shutter speed.
> Many cameras include an estimated or evaluated EV in the EXIF, I've
> discovered
>
> With today's limititions in DR of our monitors, HDR images are a stepping
> stone to the final tone mapped image. How much we need to open and view our
> HDR images will be limited, it's mostly archived information once the tone
> mapping is completed. If we decide later the tone mapped image is not to our
> liking we can begin with the HDR file again or begin with the raw files
> again. The tone mapping data would be very valuable either with the hdr or
> as a separate file like PM has now. I agree that saving the tonemapping
> settings with the output image is a good idea. Even if it has to be manually
> applied to another image, having the Tonemapping settings as file info is a
> good idea. That way it can't be misplaced, like a standalone XMP setting
> file can.
>
> I believe we should always save our original RAW files, especially the 0EV
> for that single shot metered exposure of the scene. I think it would be nice
> but somewhat redundant if the HDR image contained info that the Raw file
> has, white balance, ISO, Color Mode, Focal length, lens used, etc. It
> doesn't change between exposures so it's not critical. File size doesn't
> change between images, but it's important to see if an hdr is derived from a
> reduced image set, for speed of processing. I agree that original capture
> data about the gear, settings is a good idea to keep...for shutter speed,
> would it be possible to include all shutter speeds in the series, or the
> cheesed 'multiple values exist' way that Bridge does it when you've got
> multiple files selected
>
> On another note, I think it would be great if the HDR image had
> information of the real world dynamic range captured expressed as EV range.
> I'd like to know if the scene had a range of 6EV, 9EV or even 12EV. It would
> be valuable in learning to associate a particular scene with a dynamic
> range. That would then give us some insight into bracketing range.  Right
> now the only way to learn the DR of a scene is to spot meter the scene and
> record the EV of the darkest and lightest part of the scene or as most of us
> do, just wing it. Of course the sun would have to be eliminated from the
> calculation, as photographers we rarely want to expose for the sun's disc
> but only the blue sky around it.
>
> So I think an xmp file should have:
>
> File names
> File sizes
> Shutter speeds & f-stops
> EV's
> Dynamic Range
>
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>
>


-- 
Jack Howard
732/682-7628
www.sportsshooter.com/jackhoward
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