Difference between revisions of "Hugin Exposure tab"

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[[hugin]] has a brightness and colour correction system which is completely
+
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
+
available with the default [[nona]] stitching tool in the [[hugin Stitcher tab]].
+
  
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 predefined options do not give 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]],
+
'''exposure''', '''white balance''' and [[vignetting]] that fits the values of these points.
+
  
So for this to work, the photos in the project have to be already aligned.  Align
+
The images list behaves very similar like the image list on the [[Hugin Photos tab|Photos tab]]. So can also in this tab add/remove images, change the lens or stack assignments, link or unlink image variables,... Beside the features of the list on the [[Hugin Photos tab|Photos tab]] it provides also in-place editing of single image variables. ('''Note:''' If you want to modify a value for a lens, you need to single-click the value, not double-click it.) If you want to change image variables from several images at once, select all affected images and choice '''Edit image variables...''' from the context menu.
photos by managing control points in the [[hugin Control Points tab]] and optimising
+
geometric image parameters in the [[hugin Optimizer tab]].
+
  
'''Only use images selected in preview.''' allows you to work with just a few
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= Photometric Optimisation =
of the images in the current project rather than all of them.  Use the buttons along the top of the
+
[[Hugin Preview window]] to enable and disable source photos.  When optimising, all the hidden images will be ignored.
+
  
== Optimize Preset ==
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With Ctrl+Left click you define which parameters will be optimised. The context menu provides short cuts to select the parameters of all images, of all images of a selected lens or of all image of a single stack.
  
Use the '''Optimize Preset''' combo box to pick one of several pre-set photometric
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== Image variables ==
optimisation schemes, then click the '''Optimize now!''' button to calculate the
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In the '''Image variables''' part of the screen you can modify the exposure EV, the ''red multiplier'' '''Er''' and the ''blue multiplier'' '''Eb'''.
best available brightness and colour adjustments.
+
  
=== Low dynamic range ===
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The '''Red multiplier''' and '''Blue multiplier''' settings are used to account for changes
 +
in '''white balance''' (also known as ''colour balance'' or ''colour temperature'') between
 +
photos.  Setting them both to ''1'' will result in no ''white balance'' change (the numbers
 +
are relative to the green channel which stays unaltered).
  
This will optimise [[vignetting]], the [[camera response curve]] and '''exposure''' (EV)
+
As with exposure, different photos in the same project are quite likely to require different
for all the photos in your project.
+
''white balance''.  Typically this will be caused by variations in lighting conditions between
 +
shots - For example a cloudy scene will contain considerably less ''red'' light than the same scene
 +
under direct sunlight.
  
The exposures for all images (except for the anchor image determined by selecting
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== Camera and Lens variables ==
'''Anchor this image for exposure''' in the [[hugin Images tab]]) are optimised.
+
The values that you can change in the '''Camera and Lens variables''' table is again dependent on the '''Simple''', '''Advanced''' or '''Expert''' User interface.
  
=== Low dynamic range, variable white balance ===
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=== Vignetting ===
  
This will optimise [[vignetting]], the [[camera response curve]], '''exposure''' (EV) and
+
[[Vignetting]] is dependent mainly on your lens and the ''aperture''. Usually the
'''white balance''' for all the photos in your project.
+
centre of the image is brighter with a falloff towards the edges.  The three
 +
numbers here represent a polynomial curve used by [[hugin]] to correct vignetting.
  
Similarly to above, the exposures and white balance is optimised for all images except the
+
You are not expected to guess these values, they are generally loaded with a lens
''anchor''.
+
profile or calculated from two or more overlapping photos.
  
=== High dynamic range, fixed exposure ===
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Set the values to ''0,0,0'' for no vignetting correction.
  
This will optimise [[vignetting]] and [[camera response curve]] for all photos.
+
Usually all photos taken with the same ''lens'' will have the same vignetting, keep
 +
'''Link''' checked to ensure '''hugin''' applies the same vignetting correction to all
 +
photos with the selected lens number.
  
=== High dynamic range, variable white balance, fixed exposure ===
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=== Vignetting Center Shift ===
  
This will optimise [[vignetting]], the [[camera response curve]] and '''white balance'''
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The centre of [[vignetting]] is rarely the exact centre of the photo. The two numbers
for all the photos in your project.
+
here indicate the position of the vignetting centre. The scale is in pixels, with
 +
''0,0'' indicating the centre of the photo. The values are independent of the '''d'''
 +
& '''e''' parameters which specify the origin for projection and geometric distortion.
  
=== Custom parameters below ===
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<!-- As with other lens parameters, this '''Vignetting Center Shift''' can be optimised in
 
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the [[hugin Exposure tab]]. Keep '''Link''' checked to ensure [[hugin]] applies the same
The pre-set options are good for most situations, but often it is necessary to switch to
+
vignetting centre to all photos with the selected lens number. -->
'''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.
+
 
+
== Image Variables ==
+
 
+
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
+
in the camera itself.
+
 
+
=== 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).
+
 
+
=== White balance ===
+
 
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Also known as ''colour balance'' or ''colour temperature''.
+
 
+
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
+
stays unaltered).
+
 
+
== 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]].
+
 
+
=== 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.
+
 
+
=== Vignetting Centre ===
+
 
+
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
+
[[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
+
values.
+
  
 
=== Camera Response ===
 
=== Camera Response ===
  
[[hugin]] can optimise the [[camera response curve]] by comparing differences
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The [[camera response curve]] is used both for mapping the images to a linear
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]].
+
 
+
The '''camera response curve''' is used both for mapping the images to a linear
+
 
colourspace when creating [[HDR]] output, and for normalising the colourspace
 
colourspace when creating [[HDR]] output, and for normalising the colourspace
 
for internal vignetting, brightness and colour corrections when creating
 
for internal vignetting, brightness and colour corrections when creating
'normal' '''LDR''' output.  If your pictures don't require such corrections
+
'normal' '''LDR''' output.
then you don't really need a calibrated response curve.
+
  
Hugin uses the [http://www1.cs.columbia.edu/CAVE/projects/rad_cal/rad_cal.php EMoR response model]
+
[[hugin]] uses the [http://www1.cs.columbia.edu/CAVE/projects/rad_cal/rad_cal.php EMoR response model]
 
from the Computer Vision Lab at Columbia University which simplifies the full
 
from the Computer Vision Lab at Columbia University which simplifies the full
response curve to five empirical coefficient numbers.
+
response curve to these five empirical coefficient numbers.  You are
 +
not expected to guess these values, they are generally loaded with a lens
 +
profile or calculated from two or more overlapping photos.
 +
 
 +
Set the five numbers to ''0,0,0,0,0'' to use a generic response curve or change the '''Type'''
 +
to '''Linear''' to indicate that your input photos have a ''scene-referred'' or [[HDR]]
 +
response.
 +
 
 +
Keep '''Link''' checked to ensure '''hugin''' applies the same
 +
response curve to all photos with the selected lens number.
  
If your brightness variations are caused by lens flare then you may be better not optimising
 
'''Exposure''' or '''white balance''', instead uncheck '''Link''' for '''Camera Response'''
 
in the [[hugin Camera and Lens tab]] to optimise a different response curve for each photo.
 
  
__NOTOC__
 
 
[[Category:Software:Hugin]]
 
[[Category:Software:Hugin]]

Latest revision as of 17:30, 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 predefined options do not give the desired results you can define your custom parameters in this Hugin Exposure tab.

The images list behaves very similar like the image list on the Photos tab. So can also in this tab add/remove images, change the lens or stack assignments, link or unlink image variables,... Beside the features of the list on the Photos tab it provides also in-place editing of single image variables. (Note: If you want to modify a value for a lens, you need to single-click the value, not double-click it.) If you want to change image variables from several images at once, select all affected images and choice Edit image variables... from the context menu.

Photometric Optimisation

With Ctrl+Left click you define which parameters will be optimised. The context menu provides short cuts to select the parameters of all images, of all images of a selected lens or of all image of a single stack.

Image variables

In the Image variables part of the screen you can modify the exposure EV, the red multiplier Er and the blue multiplier Eb.

The Red multiplier and Blue multiplier settings are used to account for changes in white balance (also known as colour balance or colour temperature) between photos. Setting them both to 1 will result in no white balance change (the numbers are relative to the green channel which stays unaltered).

As with exposure, different photos in the same project are quite likely to require different white balance. Typically this will be caused by variations in lighting conditions between shots - For example a cloudy scene will contain considerably less red light than the same scene under direct sunlight.

Camera and Lens variables

The values that you can change in the Camera and Lens variables table is again dependent on the Simple, Advanced or Expert User interface.

Vignetting

Vignetting is dependent mainly on your lens and the aperture. Usually the centre of the image is brighter with a falloff towards the edges. The three numbers here represent a polynomial curve used by hugin to correct vignetting.

You are not expected to guess these values, they are generally loaded with a lens profile or calculated from two or more overlapping photos.

Set the values to 0,0,0 for no vignetting correction.

Usually all photos taken with the same lens will have the same vignetting, keep Link checked to ensure hugin applies the same vignetting correction to all photos with the selected lens number.

Vignetting Center Shift

The centre of vignetting is rarely the exact centre of the photo. The two numbers here indicate the position of the vignetting centre. The scale is in pixels, with 0,0 indicating the centre of the photo. The values are independent of the d & e parameters which specify the origin for projection and geometric distortion.


Camera Response

The camera response curve is used both for mapping the images to a linear colourspace when creating HDR output, and for normalising the colourspace for internal vignetting, brightness and colour corrections when creating 'normal' LDR output.

hugin uses the EMoR response model from the Computer Vision Lab at Columbia University which simplifies the full response curve to these five empirical coefficient numbers. You are not expected to guess these values, they are generally loaded with a lens profile or calculated from two or more overlapping photos.

Set the five numbers to 0,0,0,0,0 to use a generic response curve or change the Type to Linear to indicate that your input photos have a scene-referred or HDR response.

Keep Link checked to ensure hugin applies the same response curve to all photos with the selected lens number.