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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<title>Hugin Exposure tab - PanoTools.org Wiki</title>
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<h1 id="firstHeading" class="firstHeading">Hugin Exposure tab</h1>
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<p><a href="Hugin.html" title="Hugin">hugin</a> has a brightness and colour correction system which is completely
independent of the old <a href="PTStitcher.html" title="PTStitcher">PTStitcher</a> tool. This improved system is only
available with the default <a href="Nona.html" title="Nona">nona</a> stitching tool in the <a href="Hugin_Stitcher_tab.html" title="Hugin Stitcher tab">hugin Stitcher tab</a>.
</p><p>The <b>hugin</b> system works by sampling a spread of points for each pair of
overlapping images. The optimiser then tries to model a system of <a href="Camera_response_curve.html" title="Camera response curve">camera response curve</a>,
<b>exposure</b>, <b>white balance</b> and <a href="Vignetting.html" title="Vignetting">vignetting</a> that fits the values of these points.
</p><p>So for this to work, the photos in the project have to be already aligned. Align
photos by managing control points in the <a href="Hugin_Control_Points_tab.html" title="Hugin Control Points tab">hugin Control Points tab</a> and optimising
geometric image parameters in the <a href="Hugin_Optimizer_tab.html" title="Hugin Optimizer tab">hugin Optimizer tab</a>.
</p><p><b>Only use images selected in preview.</b> allows you to work with just a few
of the images in the current project rather than all of them. Use the buttons along the top of the
<a href="Hugin_Preview_window.html" title="Hugin Preview window">Hugin Preview window</a> to enable and disable source photos. When optimising, all the hidden images will be ignored.
</p>
<a name="Optimize_Preset" id="Optimize_Preset"></a><h2> <span class="mw-headline"> Optimize Preset </span></h2>
<p>Use the <b>Optimize Preset</b> combo box to pick one of several pre-set photometric
optimisation schemes, then click the <b>Optimize now!</b> button to calculate the
best available brightness and colour adjustments.
</p>
<a name="Low_dynamic_range" id="Low_dynamic_range"></a><h3> <span class="mw-headline"> Low dynamic range </span></h3>
<p>This will optimise <a href="Vignetting.html" title="Vignetting">vignetting</a>, the <a href="Camera_response_curve.html" title="Camera response curve">camera response curve</a> and <b>exposure</b> (EV)
for all the photos in your project.
</p><p>The exposures for all images (except for the anchor image determined by selecting
<b>Anchor this image for exposure</b> in the <a href="Hugin_Images_tab.html" title="Hugin Images tab">hugin Images tab</a>) are optimised.
</p>
<a name="Low_dynamic_range.2C_variable_white_balance" id="Low_dynamic_range.2C_variable_white_balance"></a><h3> <span class="mw-headline"> Low dynamic range, variable white balance </span></h3>
<p>This will optimise <a href="Vignetting.html" title="Vignetting">vignetting</a>, the <a href="Camera_response_curve.html" title="Camera response curve">camera response curve</a>, <b>exposure</b> (EV) and
<b>white balance</b> for all the photos in your project.
</p><p>Similarly to above, the exposures and white balance is optimised for all images except the
<i>anchor</i>.
</p>
<a name="High_dynamic_range.2C_fixed_exposure" id="High_dynamic_range.2C_fixed_exposure"></a><h3> <span class="mw-headline"> High dynamic range, fixed exposure </span></h3>
<p>This will optimise <a href="Vignetting.html" title="Vignetting">vignetting</a> and <a href="Camera_response_curve.html" title="Camera response curve">camera response curve</a> for all photos.
</p>
<a name="High_dynamic_range.2C_variable_white_balance.2C_fixed_exposure" id="High_dynamic_range.2C_variable_white_balance.2C_fixed_exposure"></a><h3> <span class="mw-headline"> High dynamic range, variable white balance, fixed exposure </span></h3>
<p>This will optimise <a href="Vignetting.html" title="Vignetting">vignetting</a>, the <a href="Camera_response_curve.html" title="Camera response curve">camera response curve</a> and <b>white balance</b>
for all the photos in your project.
</p>
<a name="Custom_parameters_below" id="Custom_parameters_below"></a><h3> <span class="mw-headline"> Custom parameters below </span></h3>
<p>The pre-set options are good for most situations, but often it is necessary to switch to
<b>Custom parameters</b>. For example, none of the pre-sets will optimise the
<b>Vignetting Centre</b>, so use custom parameters if your vignetting is off-centre.
</p>
<a name="Image_Variables" id="Image_Variables"></a><h2> <span class="mw-headline"> Image Variables </span></h2>
<p>Image variables are quite likely to vary between photos, perhaps because of minor
variations in shutter speed, changes in natural light or because of 'auto' settings
in the camera itself.
</p>
<a name="Exposure" id="Exposure"></a><h3> <span class="mw-headline"> Exposure </span></h3>
<p>The <b>Exposure</b> section shows the photo number and exposure values for all input
photos (in parenthesis), the check mark indicates parameters that will be optimised.
</p><p>When a value is set to <i>0</i> (zero) this results in <a href="Hugin.html" title="Hugin">hugin</a> applying no exposure
change to the photo. <i>EV</i> is a standard photographic scale, each increase or
decrease by one unit will change the exposure by the equivalent of one <i>f-stop</i>
(ie. halving or doubling the exposure).
</p>
<a name="White_balance" id="White_balance"></a><h3> <span class="mw-headline"> White balance </span></h3>
<p>Also known as <i>colour balance</i> or <i>colour temperature</i>.
</p><p>The <b>White balance</b> section shows the photo number and <i>red</i> and <i>blue</i>
multiplier values (in parenthesis), the check mark indicates photos that
will be optimised. If the values are set to <i>(1,1)</i>, this will result in no
<b>white balance</b> change (the numbers are relative to the green channel which
stays unaltered).
</p>
<a name="Camera_and_Lens_variables" id="Camera_and_Lens_variables"></a><h2> <span class="mw-headline"> Camera and Lens variables </span></h2>
<p>The <b>Camera and Lens variables</b> are the <i>photometric</i> analog of the <i>geometric</i> <a href="Lens_correction_model.html" title="Lens correction model">lens correction model</a>, <a href="Hugin.html" title="Hugin">hugin</a>
assumes that all input photos with the same <b>lens number</b> have identical values unless they are <b>unlinked</b> in the
<a href="Hugin_Camera_and_Lens_tab.html" title="Hugin Camera and Lens tab">hugin Camera and Lens tab</a>.
</p>
<a name="Vignettting" id="Vignettting"></a><h3> <span class="mw-headline"> Vignettting </span></h3>
<p><a href="Vignetting.html" title="Vignetting">Vignetting</a> is dependent mainly on your lens and the <i>aperture</i>. Usually the centre of the image is
brighter with a falloff towards the edges, <a href="Hugin.html" title="Hugin">hugin</a> can calculate this falloff curve as part of the
<i>photometric optimisation</i> process or you can enter it manually in the <a href="Hugin_Camera_and_Lens_tab.html" title="Hugin Camera and Lens tab">hugin Camera and Lens tab</a>
as the three numbers shown here.
</p>
<a name="Vignetting_Centre" id="Vignetting_Centre"></a><h3> <span class="mw-headline"> Vignetting Centre </span></h3>
<p>The centre of <a href="Vignetting.html" title="Vignetting">vignetting</a> is rarely the exact centre of the photo,
<a href="Hugin.html" title="Hugin">hugin</a> can optimise this position or you can enter it manually in the
<a href="Hugin_Camera_and_Lens_tab.html" title="Hugin Camera and Lens tab">hugin Camera and Lens tab</a>. The scale is in <i>pixels</i>, with <i>0,0</i>
indicating the centre of the photo. The values are independent of the
d &amp; e parameters, that specify the origin for projection and distortion
values.
</p>
<a name="Camera_Response" id="Camera_Response"></a><h3> <span class="mw-headline"> Camera Response </span></h3>
<p><a href="Hugin.html" title="Hugin">hugin</a> can optimise the <a href="Camera_response_curve.html" title="Camera response curve">camera response curve</a> by comparing differences
between overlapping images. To do this your photos need to either have
significant <a href="Vignetting.html" title="Vignetting">vignetting</a> or have variable exposure. If your photos have
perfectly even exposure and zero vignetting, then you would have to
calibrate the camera response separately and then enter it manually in the
<a href="Hugin_Camera_and_Lens_tab.html" title="Hugin Camera and Lens tab">hugin Camera and Lens tab</a>.
</p><p>The <b>camera response curve</b> is used both for mapping the images to a linear
colourspace when creating <a href="HDR.html" title="HDR">HDR</a> output, and for normalising the colourspace
for internal vignetting, brightness and colour corrections when creating
'normal' <b>LDR</b> output. If your pictures don't require such corrections
then you don't really need a calibrated response curve.
</p><p>Hugin uses the EMoR response model<a class="external" href="http://www1.cs.columbia.edu/CAVE/projects/rad_cal/rad_cal.php">[*]</a>
from the Computer Vision Lab at Columbia University which simplifies the full
response curve to five empirical coefficient numbers.
</p><p>If your brightness variations are caused by lens flare then you may be better not optimising
<b>Exposure</b> or <b>white balance</b>, instead uncheck <b>Link</b> for <b>Camera Response</b>
in the <a href="Hugin_Camera_and_Lens_tab.html" title="Hugin Camera and Lens tab">hugin Camera and Lens tab</a> to optimise a different response curve for each photo.
</p>
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