View source for Hugin Exposure tab

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.

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'''.

= Photometric Optimisation =

== 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.

<!-- As with other lens parameters, this '''Vignetting Center Shift''' can be optimised in
the [[hugin Exposure tab]].  Keep '''Link''' checked to ensure [[hugin]] applies the same
vignetting centre to all photos with the selected lens number. -->

=== 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 [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
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.