Hugin Camera and Lens tab - PanoTools.org Wiki
Keywords: Hugin Camera and Lens tab,Camera response curve,Control points,Crop factor,Cylindrical Projection,EXIF,Equirectangular Projection,Field of View,Field of view,Fisheye Projection,Focal Length

# Hugin Camera and Lens tab

The Camera and Lens tab looks a lot like the hugin Images tab, except that the lens settings can be edited here. As in the Images Tab, multi-selection can be used to change the parameters for multiple images.

Panorama Tools[*] and hugin allow the usage of images shot with different lenses and settings inside the same project. Each image is associated with a lens number. All images that share the same lens number use the same lens type, and may be forced to share the same lens parameters.

The Load lens... and Save lens... buttons allow you to keep calibrated lens profiles. Once a set of lens parameters has been obtained through lens calibration[*] it shouldn't vary much for future projects. The advantage of this is that if only positions are being optimised in the hugin Optimizer tab, then as few as two or three control points are needed per image pair.

Load EXIF examines the selected image file and tries to determine the Field of View of the photo by reading embedded EXIF data. The same function is performed when initially adding photos so you only need this button to reset the Field of View if it has since changed.

By default, every photo in a project is assigned to lens number 0. If you are including pictures taken with a different camera, a different lens or at different zoom settings; then you need to assign a new lens for these pictures by clicking the New Lens button. Assign additional photos to this lens number with the Change Lens... button.

## Geometric

The Panorama Tools lens correction model has enough parameters to model most photographic images, these parameters can be set manually here in the hugin Camera and Lens tab or calculated automatically in the hugin Optimizer tab.

Note that any or all of these parameters can be changed back to good defaults in the Hugin Reset Values window reached by clicking the Reset... button.

### Lens

The most important parameters are the Horizontal field of view and the Lens type. Hugin supports the following projections in input images:

- Normal (rectilinear) - The projection used by most cameras. It keeps straight lines straight. The maximum horizontal field of view is 180 degrees (for an image of infinite size, that is).
- Panoramic (cylindrical) - Often used by panoramic cameras, such as the Horizon, Roundshot and Spheron cameras. This projection is also called simply cylindrical projection.
- Circular fisheye - Used by fisheye lenses. If the image is circular or the corners of the image are black, use this type of fisheye lens. A circular crop in the Hugin Crop tab can be used for cutting away the edge borders.
- Full frame fisheye - Exactly the same projection as circular fisheye, but the crop option will crop to a rectangle instead of a circle. This should be used for full frame fisheye images.
- Equirectangular - A full spherical projection. These are generally created as the result of the stitching process, but it can be useful to reload a finished panorama to extract further images.

After the lens type has been specified, an estimate for the horizontal field of view[*] (HFOV) is required. The HFOV specifies the horizontal opening angle of the image in degrees. Since most photographers are more familiar with Focal Length as a measure for the HFOV, it can be entered into hugin, and hugin will compute the HFOV from it. For this calculation the actual focal length and the crop factor of the camera are required. If the 35mm film equivalent focal length is known, a crop factor of 1 should be used.

With JPEG images, hugin can usually automatically calculate the HFOV based on the EXIF information.

### Radial Distortion, Image Center Shift and Image Shearing

Usually lenses do not project images exactly according to the selected projection type, but suffer from distortions. In many cases the distortions are acceptable for single image shots, but they need to be corrected when stitching a panorama. The a, b and c parameters are used to remove that distortion. They are applied radially from the image center, which can be moved by changing the d and e parameters. These a, b, c, d and e parameters are the basis of the panotools lens correction model.

Scanned images might also suffer from image shearing[*]. This can be corrected using the g and t parameters.

The distortion parameters usually vary with the focal length, and to a lesser degree with the focus. The link checkbox indicates whether the parameter is linked or not. A linked parameter is forced to the same value for all images with the same lens number. This is the default for the HFOV and distortion parameters. If a parameter is not linked each images is allowed to have individual values for the respective parameter. This is useful if a different zoom or focus setting has been used for some images. If scanned images are used, they are usually not perfectly centered, and each image should have individual d and e parameters.

## Photometric

hugin models the photometric parameters of a lens/camera combination in a similar way to the lens correction model for Geometric parameters. These parameters can be set manually here in the hugin Camera and Lens tab or calculated automatically in the hugin Exposure tab.

Note that any or all of these parameters can be changed back to good defaults in the Hugin Reset Values window reached by clicking the Reset... button.

### Exposure and Color

Exposure (EV), EV stands for Exposure Value, setting it to 0 (zero) will result in hugin applying no exposure change to the photo.

EV is a standard photographic scale, each increase or decrease by one unit will change the exposure by the equivalent of one f-stop (ie. halving or doubling the exposure).

Very often, different photos in the same project, even those with the same lens number, will require a different Exposure. This could be because the photos were taken with a different shutter-speed or simply because the light changed between shots, if so uncheck Link here before optimising exposure in the hugin Exposure tab.

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, so uncheck Link here before optimising White balance in the hugin Exposure tab.

### 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 in the hugin Exposure tab.

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 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 in the hugin Exposure tab.

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.

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