# Hugin Stitcher tab

From PanoTools.org Wiki

The rest of hugin is all about setting up the project and aligning images, the Stitcher tab is where the final output file is created.

# Projection

Here you can set the output Projection of your project, there are lots to choose from, each with different advantages and disadvantages:

- Rectilinear, this is the same projection as a photo taken with a 'normal' camera and lens. Use this if you are just stitching a handful of photographs together with a narrow Field of View or correcting perspective in a single shot.
- Cylindrical, actually a simple Cylindrical Projection as used by traditional rotating panoramic cameras. A good projection for printing a 360 degree panorama, though you may prefer Mercator Projection.
- Equirectangular, the all purpose format for representing an entire spherical scene. It covers 360 degrees horizontally as well as the zenith and nadir.
- Fisheye, the same projection as a photo taken with a fisheye lens. Better for representing a wide Field of View than rectilinear, but in many cases Stereographic Projection gives less distortion than simple fisheye.
- Stereographic, a conformal fisheye image. Objects in a stereographic image keep the same shape and show less distortion than simple fisheye.
- Mercator, a conformal cylindrical image. A good projection for printing a 360 degree panorama.
- Trans Mercator, a mercator image rotated 90 degrees, suitable for displaying tall or overhead objects.
- Sinusoidal, an equal area projection of an entire spherical scene.
- Lambert Cylindrical Equal Area[*]
- Lambert Equal Area Azimuthal[*]
- Albers Equal Area Conic[*]
- Miller Cylindrical[*]
- Panini
- Architectural[*]
- Orthographic
- Equisolid
- Equirectangular Panini
- Biplane[*]
- Triplane[*]
- Panini General
- Thoby Projection, is modeling the 10.5 mm Nikkor fisheye lens and was introduced with hugin 2011.0.0. The projection is called after Michel Thoby who was able to empirically find it.
- Hammer-Aitoff Equal Area Projection

# Field of View

This is the horizontal and vertical angle of view of the output image, clicking Calculate Field of View will shrink or enlarge the field of view of the output to fit the arrangement of the input images - The Fit button in the Hugin Preview window does the same thing.

Note that some Projections have a limited field of view, notably:

- Rectilinear has to be less than 180 degrees both vertically and horizontally.
- Panoramic (cylindrical) has to be less than 180 degrees vertically.
- Stereographic has to be less than 360 degrees both vertically and horizontally.
- Mercator has to be less than 180 degrees vertically.
- Transverse Mercator has to be less than 180 degrees horizontally.

# Canvas Size

Set the width and height of your output panorama in pixels. Calculate Optimal Size will estimate a size that has about the same resolution as your input images.

Some examples: a three megapixel image has pixel dimensions of 2048 x 1536, an A4 print at 300 pixels per inch will have a pixel size of 3500 x 2480, a full screen spherical Equirectangular Projection image will have pixel dimensions of 6000 x 3000 or greater and a gigapixel image has a pixel size of 32768 x 32768.

Note that the interpolation used by hugin doesn't handle downsampling very well, so output images smaller than about half the size of the Optimal Size will show aliasing artefacts. If you want to create high quality small images, it is better to create an Optimal Size image in hugin and downsize it later in an image editor such as Gimp[*].

# Crop

The crop settings allow just a portion of the panorama to be stitched, there are various reasons to do this:

- When correcting perspective large areas of the panorama output will be empty anyway.
- Large 'gigapixel' style panoramas can be stitched in sections then blended later.

The cropped-out areas are shown darkened in the Preview window.

The Fit Crop to Images button will automatically determine a crop that has a maximum number of pixels and no empty space. This is the same function as the Autocrop button in the Fast Preview window.

# Panorama Outputs

Hugin can output 'normal' stitched images, exposure fused[*] images or high dynamic range (HDR) images. The following options determine which kind of image is created, and allow keeping the intermediate images created during the process.

## Normal

If Exposure corrected, low dynamic range is enabled then enblend is used for blending. In the final stitching process nona reprojects and distorts images to fit, enblend takes these images as individual TIFF files and merges them using sophisticated seam positioning and blending. Further enblend settings can be found in the hugin Preferences.

Enable Exposure corrected, low dynamic range under Remapped Images if you want to keep the intermediate images that enblend uses as input - For example modifying the alpha channel of these images and then blending manually is one technique for including and excluding people or objects that move between shots.

## Exposure fusion

If Exposure fused from stacks is enabled then hugin will group the input images into exposure stacks by comparing positions, any images with more than 70 % overlap are grouped like this. Each of these bracketed exposure stacks will be exposure fused[*] with enfuse and the results seam blended together into a panorama with enblend.

Notes:

- For this to work, the scene has to be photographed multiple times using exposure bracketing and the EV exposure values set either manually in the Photos tab, automatically from EXIF data or by optimising exposure in the hugin Assistant tab or hugin Exposure tab.

- Note also that unlike Normal and HDR merging options where images are exposure corrected as part of the remapping process, enfuse requires that each exposure layer is supplied uncorrected - Hugin takes care of this automatically and will not apply exposure correction in this case.

- If you want to keep the exposure fused stacks for manual blending tick the option Exposure fused stacks from Combined stacks.

- For special cases the percentage for decision for the overlap can be fine-tuned (only in expert). Go to Images tab[*] and select group by output stacks and change the minimum overlap value. If you want to use the already assigned stacks instead of the deduced stacks, set the minimum overlap value to -1.

If Exposure fused from any arrangement is enabled then hugin will seam blend images with similar exposure with enblend and than it will exposure fuse[*] them using enfuse. This variant is often much more successful than Exposure fused from stacks in two situations:

- Where entire panoramas have been shot at each EV level consecutively rather than each shot bracketed, in this case it isn't guaranteed that shots will line up into the approximate stacks expected by the Exposure fused from stacks option.

- When the panorama has been shot entirely on automatic exposure, in this situation it is useful to seam blend adjacent photos with small EV differences, but then exposure fuse larger EV differences - As effectively happens with this option.

Note that Hugin uses a default threshold of 0.5 EV exposure difference to determine which photos can be fused into each layer. This threshold can be modified on the Photos tab in the Expert mode (selecting group by Output layers).

Enable Blended layers of similar exposure, without exposure correction from Layers to keep exposure layers from the Exposure fused from any arrangement step, these are useful for manual Contrast Blending[*].

Enable No exposure correction, low dynamic range from Remapped Images to keep the intermediate images supplied to enblend and enfuse.

The output format of Normal and Exposure fusion can be in one of several output file types:

- TIFF, various compression options. 16 bit and 8 bit depth supported. None compression is supported by most other applications, LZW compression is common in Windows/Mac applications and Deflate compression is more common with Linux tools.
- JPG, lossy compression suitable for web/email. Quality can vary from 0 (extremely low quality, small file size) and 100 (high quality, large file size). A typical quality setting for web/email would be between 70 and 80
- PNG, lossless compression. 16 bit and 8 bit depth supported.

## HDR merging

The option High dynamic range is only available in Advanced and Expert mode.

If High dynamic range is enabled then hugin will identify likely bracketed stacks of images, then create remapped HDR images which are then blended with enblend.

Note that like the Exposure fusion option above, this generally only makes sense if the scene has been photographed multiple times using exposure bracketing. This option works also for creating panorama from HDR input images.

Enable High dynamic range merged stacks from Combined stacks to keep copies of the remapped HDR images as supplied to enblend.

Enable High dynamic range from Remapped Images to keep copies of each image remapped in linear colour space before merging to HDR. High dynamic range Format can be either:

- floating-point TIFF, various compression options.
- EXR, this is a high dynamic range format which is more compact than a high dynamic range TIFF.

# Processing

nona is the default Remapper (stitching engine) supplied with hugin, normally there is no need to change this or any of the options below.

Set the Interpolator (i) to change the sampling interpolation. You probably won't notice much difference between the various options except that Nearest Neighbour is fast but with very low quality. The default of Poly3 (bicubic) is generally good for most purposes.

Cropped TIFF files are smaller and more efficient because unused parts of the image are not stored in the file. You should always save cropped images unless you need to open them in an image editor without Cropped TIFF support.

enfuse is the default for Exposure fusion[*], Options are similar to enblend.

The default HDR merger is hugin_hdrmerge[*].

enblend is the default Blender for use with hugin, normally there is no need to change this. Additional command-line Options can be set here or in the hugin Preferences for new projects.

# Stitch

Click Stitch! (located in the bottom right corner of the window) to generate output panoramas. With default setting the current project is added to the Hugin Batch Processor stitching queue. Note that the queue won't be processed unless this queue manager is running.

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