12. January 2009, 09:39 clock
DIGITAL PHOTOGRAPHY
pro tips for great panoramic views
to tinker For each photo a powerful panorama, which requires some basic knowledge. Professional photographer Michael Freeman explains what stitching, how to make a 360-degree panoramic view of a single image, and how transitions between images succeed clean.
technologies that claim to promote creativity, I am naturally skeptical. But in the case of multiple images Anstückelns (jargon "stitching") I make an exception.
| For a variety of frames of several sequences of eight images were selected to this panoramic impression from the studio of the Chinese artist Shao Fan to make |
The technology behind this very simple concept has dramatically during the last few years. Basically, stitching nothing but the combination of several overlapping images into a single, larger picture.
stitching software has the analog days, almost unthinkable in the process of joining together of 360-degree panoramas or large images of several individual shots as easily never done before. These opportunities offer an inexhaustible creative potential and have even found their way into the art of photography.
Huge images create
The assembly of a single, huge image of many individual images increases the resolution of the final image. Rather than take a subject with a focal length of 50 mm, zoom simply approached 100 mm detailed and bright, overlapping areas of the image from. The end result is an image file, which is four times as big - as if it had been made with a camera that has a much higher sensor resolution. In the analog era it was forced to switch for high-resolution images on an expensive large-format camera. Even today you can outrageously expensive digital backs with 15 megapixels or more to fall back - or you simply multiply the resolution of your current camera through the use of stitching. To do this, divide the scene into several segments - the longer the focal length, the more segments. This allows a multi-telephoto image file can be huge in size - to expect do have a look.
A 15-mm lens on a DSLR with a full image sensor covers a viewing angle of 110 degrees, which corresponds to a real wide angle shot. Now imagine the same scene with a 120 mm lens in front, divided into small segments. The 20 degree full view of the telephoto lens can be divided into 64 segments, which results in regards to the necessary areas of overlap around 100 frames. If you use a 10 megapixel camera would end up with a picture file with the dimensions are 31 000 x 21 000 pixels. This corresponds to a virtual camera with a 640-megapixel sensor!
In practice, however, you must face some serious drawbacks. First, does the Anstückeln much time and patience. Second, it is almost exclusively for static subjects. And thirdly, you need an extremely powerful computer, perform the necessary processing steps in a reasonable time to - the above example would result in a two-gigabyte image file by itself.
Nevertheless offers stitching at all times when a higher resolution is required. All you need is time, software and a tripod head that allows you to rotate the camera around the virtual focal point around, so that perspective distortions are minimized.
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A single shot of the skyscrapers of Pudong in Shanghai, were taken with a focal length of 80 mm on a 12-megapixel camera (4100x2800 Pixels).
nine overlapping frames of the same scene with a focal length of 200 mm give a picture file with 15 300 x 4000 pixels - equivalent to a resolution of 61 megapixels.
panoramas
panoramic images are the most important application for stitching software - not surprising, because the results are exciting and impressive for many reasons. Panoramic images are much wider than high, and there is no absolute benchmark for aspect ratio are - generally, anything over and above the 3:1 format, be regarded as a panoramic. Why panoramic images are so popular? It is possible that the same cause as the popularity of wide-screen formats in film and television - we are used to scan large-scale scenes such as landscapes and horizontally to explore in this way with our views. Panoramas provide a superior feel for the real sight of the shooting scene. Here there are no limits - even 360 ° views are possible by a full rotation of the camera.
can in terms of image composition, you can learn from the way the cinematic. A popular approach is the "pulling apart" of the composition in the width. Unlike the conventional 3:2 format of digital cameras, you can easily format panoramic two or three motifs combine in an image. The integration of the dominant foreground helps give more depth to the panorama to the eye and reveal even more details to explore.
panoramas work best across a large depth of field over the entire distance, so you should focus elements are avoided.
An important side effect of the stitching, the resulting, large image file with many details and much higher resolution, so that also be worth the high-format photography can. , To determine the long axis of the image height of the panoramic image. The only problem with this approach is the correct tripod mount - I personally prefer an L-shaped mounting on a tripod head with quick release.
| Michael Freeman |
Asia's largest LCD display is mounted on the ceiling of a shopping center in Beijing. Their size and position require a strong bent angle, so that the final image has a strong image distortion curve, the surreal impression of the scene reinforced.
The circular house of the Hakka clan, Tulou called, is located in the Chinese province of Fujian. make His great extent and the limited viewing angles make it an ideal panoramic image. With a focal length of 18 mm, I made five separate images in portrait mode. A second sequence was used to increase the depth. find
ideals overlap areas
is the stitching via software in three steps. First the program determines the matching pixels in the overlapping areas, so that the frames are strung together seamlessly. Second, the levels of the images are aligned. And thirdly, all source images are fused into a whole.
this step one can be run properly must include the overlapping areas enough details so that the software can easily identify the points of intersection. Ideally, you have to make the source images with small overlap areas to not have to make more images than necessary. Sharp and clearly identifiable image elements of the software easier to interpret than homogeneous areas without major differences such as white walls or overcast sky. An overlap of about 40 percent between images is usually sufficient, and it depends on the level of detail of the scene. I even facilitate my work, as I always the source images by half the image width to overlap. In practice this means that an object at the edge of the first frame in the middle of the second recording reappears. Since I always take pictures in this way, I go quite fast panoramic series of hand - I must make during the recording not worry about the size of the overlapping image regions.
The four source images from this installation in an art gallery overlap by about 40 percent. In each region of overlap there are enough details on which can guide the stitching software.
The consistency in the scene eighth
The second step is the stitching procedure, as described on the last page, the mesh screens of different source images, with both the levels and the colors are aligned. An identical on all the frames white balance makes the software work immensely. This also applies to other settings, including the exposure time. For this reason, you should turn off the automatic mode, the camera and make the necessary adjustments manually. A screen test helps you determine the correct values for all frames.
As in 360 º-degree panoramas usually one or more light sources are included (especially outdoors on a sunny day), could in some source images cropped lights or truncated shadows creep - the dynamic range of the camera is exceeded. The solution is to make multiple images with different exposure for each frame to be assembled later into an HDR image.
As so often, is also recommended for the panoramic photography, the use of the raw file so you can make the necessary corrections directly in the raw converter. An interesting technique is the progressive variation of the color balance over the panorama of time - for example in the area of a window with the setting "Daylight" and toward the interior, using the "artificial light". The stitching software then displays the different images together seamlessly.
This example demonstrates an approach that from the principle of identical white balance different.
The four source images were in raw format, customized with automatic white balance, so that the color temperature is changed from left to right (1 = 5500K, 2 = 4500K, 4000K 3 =, 4 = 3300K).
The reddish discoloration on the right side of the window was removed in the image processing software by replacing colors. By comparison, a recording with the same white balance (tungsten). determine
the virtual focal point
Normally, the software does the overlap of two images a good job by making the necessary, compensates by different angles resulting distortions. But when it comes to Parallaxverschiebungen that may occur through minimal changes to the camera position, possibly resulting ghost images of objects in the foreground. Of course the camera must be the making of a Panorama series moved - but only about its axis of rotation. And this axis must deal with the virtual focus of the lens are in harmony. This focal point is like the optical center of the lens (which may not necessarily be due to the lens elements in the physical center of the lens). With a zoom lens, this point moves with the focal length.
can with a simple trial and error method, this point for each lens Dashboard. Panorama supports for tripods can be fixed to certain positions. If the virtual focal point covers exactly with the rotation axis of the bracket, there is no Parallaxverschiebungen. See the viewfinder two closely spaced, vertical contours, which should be a close and the others are in the distance. Turn the camera and keep the distance between the two contours in the eye. If this distance is significantly changed, move the camera a little forward or backward, so that the distance remains the same after rotation. This is very good to see from the example panoramas on this site.
Figures 1 and 2 were made at a focal length of 14 mm for the determination of the virtual focus. Figure 3 was used as a reference. The distance between the drainpipe and the window frame in Figure 1 indicates a significant Parallaxverschiebung, which was eliminated by moving the camera forward and back.
is the virtual focal point of the lens exactly on the axis of rotation of the tripod-mounted panoramic bracket.
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