Difference between revisions of "Hugin Exposure tab"

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[[hugin]] has a brightness and colour correction system which is completely
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As explained on the [[Hugin Photos tab#Photometric_.28Simple_User_interface.29|Hugin Photos tab]] hugin has a brightness and colour correction system using the default nona stitching tool.
independent of the old [[PTStitcher]] tool.  This improved system is only
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available with the default [[nona]] stitching tool in the [[hugin Stitcher tab]].
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The '''hugin''' system works by sampling a spread of points for each pair of
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Hugin comes with an extended set of predefined settings for photometric optimisation. If these do not gice the desired results you can define your custom parameters in this '''Hugin Exposure tab'''.
overlapping images.  The optimiser then tries to model a system of [[camera response curve]],
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'''exposure''', '''white balance''' and [[vignetting]] that fits the values of these points.
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So for this to work, the photos in the project have to be already aligned.  Align
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photos by managing control points in the [[hugin Control Points tab]] and optimising
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geometric image parameters in the [[hugin Optimizer tab]].
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'''Only use images selected in preview.''' allows you to work with just a few
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of the images in the current project rather than all of them.  Use the buttons along the top of the
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[[Hugin Preview window]] to enable and disable source photos.  When optimising, all the hidden images will be ignored.
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== Optimize Preset ==
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Use the '''Optimize Preset''' combo box to pick one of several pre-set photometric
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optimisation schemes, then click the '''Optimize now!''' button to calculate the
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best available brightness and colour adjustments.
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=== Low dynamic range ===
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This will optimise [[vignetting]], the [[camera response curve]] and '''exposure''' (EV)
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for all the photos in your project.
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The exposures for all images (except for the anchor image determined by selecting
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'''Anchor this image for exposure''' in the [[hugin Images tab]]) are optimised.
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=== Low dynamic range, variable white balance ===
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This will optimise [[vignetting]], the [[camera response curve]], '''exposure''' (EV) and
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'''white balance''' for all the photos in your project.
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Similarly to above, the exposures and white balance is optimised for all images except the
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''anchor''.
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=== High dynamic range, fixed exposure ===
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This will optimise [[vignetting]] and [[camera response curve]] for all photos.
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=== High dynamic range, variable white balance, fixed exposure ===
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This will optimise [[vignetting]], the [[camera response curve]] and '''white balance'''
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for all the photos in your project.
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=== Custom parameters below ===
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The pre-set options are good for most situations, but often it is necessary to switch to
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'''Custom parameters'''.  For example, none of the pre-sets will optimise the
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'''Vignetting Centre''', so use custom parameters if your vignetting is off-centre.
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== Image Variables ==
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Image variables are quite likely to vary between photos, perhaps because of minor
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variations in shutter speed, changes in natural light or because of 'auto' settings
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in the camera itself.
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=== Exposure ===
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The '''Exposure''' section shows the photo number and exposure values for all input
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photos (in parenthesis), the check mark indicates parameters that will be optimised.
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When a value is set to ''0'' (zero) this results in [[hugin]] applying no exposure
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change to the photo.  ''EV'' is a standard photographic scale, each increase or
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decrease by one unit will change the exposure by the equivalent of one ''f-stop''
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(ie. halving or doubling the exposure).
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=== White balance ===
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Also known as ''colour balance'' or ''colour temperature''.
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The '''White balance''' section shows the photo number and ''red'' and ''blue''
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multiplier values (in parenthesis), the check mark indicates photos that
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will be optimised.  If the values are set to ''(1,1)'', this will result in no
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'''white balance''' change (the numbers are relative to the green channel which
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stays unaltered).
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== Camera and Lens variables ==
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The '''Camera and Lens variables''' are the ''photometric'' analog of the ''geometric'' [[lens correction model]], [[hugin]]
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assumes that all input photos with the same '''lens number''' have identical values unless they are '''unlinked''' in the
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[[hugin Camera and Lens tab]].
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=== Vignettting ===
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[[Vignetting]] is dependent mainly on your lens and the ''aperture''.  Usually the centre of the image is
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brighter with a falloff towards the edges, [[hugin]] can calculate this falloff curve as part of the
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''photometric optimisation'' process or you can enter it manually in the [[hugin Camera and Lens tab]]
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as the three numbers shown here.
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=== Vignetting Centre ===
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The centre of [[vignetting]] is rarely the exact centre of the photo,
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[[hugin]] can optimise this position or you can enter it manually in the
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[[hugin Camera and Lens tab]].  The scale is in ''pixels'', with ''0,0''
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indicating the centre of the photo. The values are independent of the
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d & e parameters, that specify the origin for projection and distortion
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values.
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=== Camera Response ===
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[[hugin]] can optimise the [[camera response curve]] by comparing differences
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between overlapping images. To do this your photos need to either have
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significant [[vignetting]] or have variable exposure.  If your photos have
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perfectly even exposure and zero vignetting, then you would have to
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calibrate the camera response separately and then enter it manually in the
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[[hugin Camera and Lens tab]].
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The '''camera response curve''' is used both for mapping the images to a linear
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colourspace when creating [[HDR]] output, and for normalising the colourspace
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for internal vignetting, brightness and colour corrections when creating
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'normal' '''LDR''' output.  If your pictures don't require such corrections
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then you don't really need a calibrated response curve.
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Hugin uses the [http://www1.cs.columbia.edu/CAVE/projects/rad_cal/rad_cal.php EMoR response model]
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from the Computer Vision Lab at Columbia University which simplifies the full
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response curve to five empirical coefficient numbers.
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If your brightness variations are caused by lens flare then you may be better not optimising
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'''Exposure''' or '''white balance''', instead uncheck '''Link''' for '''Camera Response'''
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in the [[hugin Camera and Lens tab]] to optimise a different response curve for each photo.
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__NOTOC__
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[[Category:Software:Hugin]]
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Revision as of 13:15, 30 January 2013

As explained on the Hugin Photos tab hugin has a brightness and colour correction system using the default nona stitching tool.

Hugin comes with an extended set of predefined settings for photometric optimisation. If these do not gice the desired results you can define your custom parameters in this Hugin Exposure tab.