Dieter Brors
Perfect Photo Panoramas
special topic: Step by step to the final round picture using Hugin
The open-source software can certainly compete with commercial Hugin panoramic programs. But the lack of documentation and the numerous adjustment possibilities make it difficult for the beginner to achieve a presentable result. In this workshop we will show you how in just a few steps still create.
updated articles from c't 21/06Compared with commercial programs such as PanoramaStudio offers free Hugin some merit. Shall suspend the program along several rows of overlapping photos into a single picture, making it easy for example, house of a tight market place representing the full amount. It is sufficient to tilt the camera slightly and make a second or third row of the scene. It is only necessary to ensure that the photos and vertically by about one third overlap. A tripod is not necessary for the recordings, as well Hugin with ink paintings cope.
As incurred during assembly of the photos (stitching) a lot of computation and huge amounts of data, Hugin is quite high hardware requirements. It is recommended that a fast computer with as much RAM, and 512MB apply as an absolute minimum. Better are 1 gigabyte, which shortens the Stitcher runs clear. For Windows there is the additional tool autopano-sift that automates much of the work. In the current Windows installation package that is included, so that it does not need to set up further. Linux is a variant called autopano-sift-C available. Sorry missing for Mac OS X such a tool, so Mac owners need to invest more time and manual labor for their views.
basis for this workshop is the Windows version, configuration and use, but on Linux and Mac OS X almost identical. All necessary steps are the way to see in the picture gallery in full size.
Those interested in more details and background information, or even Special Functions of Hugin, found on the internet a very detailed tutorial . Among other things, it shows what can be correct converging lines in architectural photography.
laborers
After installation of Hugin should check some settings on the first start and, if necessary. enabled "Use alternative Autopano-SIFT application" under "File / Preferences" tab has Autopano of entry and in the selection list "Autopano-SIFT (by S. Nowozin)" selected. In addition, the path to the application are correct, the bin in a default to "Autopano-sift-c.exe" in the directory of the Hugin folder has. All other settings are for fine tuning, especially for specialists. You can initially remain unchanged.The typical process is to load the pictures and in the setting of so-called control points in the overlapping area of all images. These points can mark identical points and provide the necessary information, put together with those of the individual images Stitcher seamlessly and align the different perspectives. Since the control points determine the quality of the generated panorama, the main work was as they sent to distribute. This work is both Windows and Linux users can delegate to autopano-sift to find the basis of color differences automatically appropriate agencies.
Back and forth
Unlike earlier versions of Hugin now contains a wizard, which lets you can create panoramas in three steps. It is sufficient to load the images to align and to create the final panoramic image. But this often does not lead to some notable successes, such as when control points in cloud formations or in branches of trees have been set that have moved between the single images and produced the automatic therefore incorrect views.Despite the wizard to get the manual assembly the individual images in the long run are not around. Although the surface is all the steps from loading the pictures before roughly to the output of the finished panorama on tabs. But who simply executes the pages from left to right will hardly achieve the expected result. This produces a high quality Hugin result, the user must always insert interim steps and move from one tab to another back and forth. There is also a large number of parameters that require a lot of expertise that would otherwise be embraced in the first - especially as more detailed information in the online documentation is missing. Whoever does either of them, the result of deteriorated much more than that he improved. Fortunately, you have to But do not bother with literature, because most of these settings, the program calculates automatically.
first step is to load on the tab "Pictures" to the individual photos. In general, the photos from the camera and are numbered consecutively in the same directory, so just click "Add As a result of recorded images" button is enough to import a dialog ( step 1). On "Individual images Add the still images can be individually and load from different folders. If you have it read in photos, not part of the panorama, they can be in the file view deleting Hugin. If not the pictures be taken from left to right, should the order according to order by each image shifts. Although does the order not to merge the images, but simplifies the editing of control points, the selection of adjacent images.
default marked Hugin the first frame of a series as the anchor frame where the program aligns all the other photos and aligning brightness and perspective. Hugin A distinction between position and exposure anchor and this marked the anchor column of the file list with "A" position and "C" for brightness. Since the frames are usually exposed to different, it should be assigned to the exposure anchors the picture with optimum brightness to make the panorama does not get too dark or too light. This can be done after selection of image "set exposure anchor" a click on the button (step 2 ). Regardless of the exposure should be assigned to the anchor position anchor the middle picture, in that these depends on the perspective of the final image and the Stitcher all the lines and the horizon hosting it ( step 3). Leaving it to one of the preset position, protrudes the panorama from one edge to another sometimes extreme up or down and so distorted the content - sometimes beyond recognition. The parameters for the image orientation (in the German version of yaw, pitch angle and roll angle is called) can be ignored because Hugin calculated independently.
determine on the tab "camera lens" you should then control settings. If the image files EXIF information mentioned, you must set the main parameters by hand. It is sufficient to select the first image and activate the box "Link" to save the settings for all other photos ( step 4). Relevant here are the type of lens, with wide-angle lenses are considered standard lenses "Straightforward (rectlinear)", which is the default. In addition, information on the focal length used and the form factor of the camera (or extension Crop factor) needed depends on the sensor size. Who does not know the values of his camera, she finds in the manual. For the angle should be a rule, a value 60-70 Degrees, which corresponds to a standard lens. The other settings can be like the correction of distortion or displacement or the displacement of the center ignore you again because they Hugin also calculated.
order to let the control points on both Windows and Linux, automatically, you have to change then back to the tab "Pictures". There are "create control points" is the button. The field next to the button indicates the number of points per image pair before ( Step 5). Here it is appropriate to maintain the preset with 10 control points and the value only increased to, for example, 20 when the final image was not assembled correctly. According to Hugin Developer are not scheduled to reach only three of these points, but higher values to improve EBIT significantly. Create control points "After clicking on a command line Autopano starts. After a short time - on a Pentium 4 / 1, 8 with 1 GB of RAM and nine individual images, this will take just under three minutes - reports a window displays the number of control points.
tinkering on the tab "control points" then falls to the main work. Mac users will need here the salient points within the overlapping areas indicate by hand. But Windows and Linux users should spend some time here to check the automatically generated items and revise if necessary. Often they distributed Autopano namely uneven, sometimes they refer to entities such as branches, cars or people who have moved between shots. This is true but its position in the two images do not match, so the stitcher can not put together correctly. Three automatic functions support all operating system versions to the user by setting a point at the corresponding point found in the adjacent picture. For this, the automatic fine-tuning, adding and resources must be activated by clicking on the appropriate box (Step 6 ).
check then you choose to set a point from two adjacent pictures to side by side. Clicking on a prominent place in the overlap of the two images shows an enlarged section first, so you can position the mark exactly, and, with another click ( step 7). Hugin then marks in the adjacent picture the same place where it is located in the overlapping area (step 8 ). To remove an unfavorable set of control, it is sufficient to select it and press the delete key.
when marking the control points, one should avoid the edges of images, since lenses easily create distortions in these areas, especially in wide shots. You should also highlight any possible objects in the foreground as the camera rotation between the pictures, especially in the foreground leads to parallax. In order to shift the front side and background, so the two images show different parts of the scene that the stitcher can not put together correctly. In the background the effect is difficult, so that the control points as possible should concentrate on him.
If the anchor picture be seen as building facades or window frame, helping to define one or more horizontal and vertical lines while eliminating distortion. This is chosen in the left and right view of the same picture and turns off all three automatic options. After the setting of a point in the left view, such an upper corner of a window frame, marked one in the right view the lower corner ( step 9). Clicking the right mouse button or the "Add" defines the part of the picture as a vertical or horizontal line, with Hugin detects the type itself. If not, the line can be in the list of control points by selecting the item on the list correct "mode" (step 10 ).
After setting or changing the control points of each pair of images, the optimization feature of Hugin always check and optimize the settings. This one changes to the page "optimization" and choose in the list box first "orientation (incrementally, starting from anchor)". Start optimizing "Clicking starts running (step 11 ). In the end displays a dialog to statistics, in particular about the quality of the control points and thus about the expected result gives practical, with an average control point distance is less than 5 indicates a good result ( step 12). Dialogue with the question of whether changes should be taken as you close in this case "yes". Determines the optimization run a higher value than 5, you should spread a negative reply and the control points evenly. After this is done in all images pairs, an additional optimization run by selecting "All" to calculate the missing parameters for stitching ( step 13).
coffee break only after this optimization run, it pays to go to the tab "assembly" and making the output format and some additional settings. As projections are for normal panoramas "Spherical (Equirectangular)", So the picture on a ball, or "cylindrical" in question (step 14 ). The rectangular figure (item "Straight-line (rectilinear)") is indeed horizontal lines are straight, but is suitable only for small series of images from two or three photos because the image content to the edge more and more distorted. It is particularly suited to still images captured in buildings put together a mosaic. Cylinders with up to 360 degrees, the usual example of QuickTime panoramas, which is using the mouse to rotate as a viewer. The
via the View menu, expandable Preview allows control of the expected prior to stitching panoramas ( step 15). Here you can very well choose to see the impact of the selected image onto a different picture and, if necessary. Two faders can crop the image horizontally and vertically, which is unnecessary in many cases, post-processing in a separate image editing program ( step 16). For quick assembly, it is sufficient to choose the back to the Hugin-surface on the tab "joining" the result is "Panorama". If you want to view panoramas only on screen, it's not worth the maximum size determined by Hugin maintain because a finished panorama can occupy several hundred megabytes. In addition, a Stitcher run easily take over half an hour, the reduction to the required level speeds up the process considerably. This changing in the appropriate fields, the width, determined from the Hugin up. Please click on "now joining" opens a dialog, the file name and directory queries for output image, and then starts the run-Stitcher ( step 17).
Since the preview, but it gives an impression of the finished panorama, but shows no details in the transition areas, it pays to produce only a test pattern such as screen width in order to look for errors. Then you can optimize the control points as needed and only at the end Create the actual view in full resolution.
banish ghosts
Some errors can not resolve by reworking the control points. Has the scene such as people, cars or ships, which have moved during the recording, sometimes resulting in the overlapping area so-called ghost objects that appear twice or transparent. These errors can be quite easy to fix in any image editing program. This will initially be run with a special stitcher option enabled Converted frames for the output. In this way, namely by Hugin expects all the frames, but omits the last step you can make up for the processing of the images from the command line. For these files you charge one of the pictures with the unwanted object in the overlapping area in an image editing program like Gimp and clears the area with the eraser tool, which will be marked as transparent. Using the command line tool Enblend, which is located in the Hugin directory, can be put together after the panorama. This one changes in the Hugin folder and call enblend with the name of the output file and the individual images in the correct order to, for example:enblend.exe-v-w-oe: pano.tif pano1.tif pano2.tif pano3 . tif
This can catch the transparent area and superimposed it completely with the contents of the adjacent image, which the ghost object is gone.
Who has made with the individual steps once familiar and invested some effort in the correction of the control points, get a little exercise without excessive expenditure of time to some notable successes. Perfectionists but can also look for days so that to remove even the smallest discrepancy in the transitions. In most cases, but our already rich quick passage to impress viewers. (Db )
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