# The PanoramIX Authoring Tool

## Version 0.1.4.92, February 26, 1998

### 5.2 Camera Properties

The Camera Properties dialog allows one to specify the properties of the camera used to capture the images comprising the panoramic scene. This dialog is opened by selecting the Camera entry in the Options menu.

The principal purpose of this dialog is to establish the field of view angles for imported images comprising the panoramic scene. As long as the same camera, lens, and lens settings are used for all images, these angles will be the same for all images. If the field of view angle is known, it can be entered directly in the Field of view field. The alternative is to enter the camera properties needed to calculate the field of view.

Setting the camera properties with this dialog is needed only when importing images with the Direct Image Import method described above. This is not required for images specified in Raw Image Control Files.

The camera properties have no effect on panoramic images or sprites. In addition, these settings have no effect on subsequent images specified in Raw Image Control Files. Side images specified in Raw Image Control Files have their own field of view angles which take priority over the values specified in the Camera Properties dialog. After reading a Raw Image Control File with side images, the Camera Properties will reflect the conditions implied by the data in the Raw Image Control File.

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### 5.2.1 Camera Body Types

The first portion of the Camera Properties dialog allows one to specify the type of camera body used to capture the images. The choices here are (a) standard 35mm film, (b) 35mm digital camera, (c) Kodak DC40, or (d) other.

#### 5.2.1.1 Standard 35mm Camera Body

The standard 35mm film option assumes a standard image size of 36mm wide and 24mm high. These dimensions may be used to determine the field of view for images scanned from full negative prints. Unfortunately, it is common practice to crop away portions of images near the edges, because these edges tend to look fuzzy and ugly. Unless the images are scanned from contact prints or proof sheets, the scanned images usually represent an area less than 36mm wide and 24mm high. In addition, if the prints do not have a 3:2 aspect ratio, part of the full image has been lost. For example, a 4x5 or 5x7 print from a 35mm negative cannot represent the entire negative. In order to have a full negative print, the dimensions of the print may be 4x6, 5x7.5, and so forth. If the scanned prints do not represent the entire area of the original negatives, then the focal length specified for the lens must be adjusted to compensate for the fraction of the negative actually contained in the print.

#### 5.2.1.2 35mm Digital Camera

The 35mm digital camera body option is provided for images obtained from professional digital cameras that can accommodate standard lenses compatible with 35mm film cameras. Although these cameras use the same lenses used by 35mm film cameras, the images are captured on electronic image detectors (usually CCDs or charge coupled devices).

The problem with these cameras is that the CCDs typically do not occupy the same 36mm by 24mm area used to capture images in a standard 35mm film camera. This causes the field of view angle of the captured images to be reduced compared to that obtained with the full negative in a 35mm film camera. In order to compensate for the reduced size of the image capture area in a 35mm digital camera, the focal length specified for the lens must be increased by the ration of the CCD size to the 35mm film size (36mm by 24mm). The result is the "35mm film equivalent focal length", or the focal length of the lens which would give the same field of view on a standard 35mm film camera.

In most cases, the manufacturer of a 35mm digital camera may not provide sufficient information to determine the conversion from the nominal focal length of a lens to the 35mm film equivalent. The ratio of the 35mm film equivalent focal length to the nominal focal length (the value declared on the lens), however, is a constant for the camera body and is independent of the particular lens. Therefore, for the first set of images captured with such a camera, it may be necessary to perform some calibration exercises and to go through some guessing and refinement of estimates until the correct factor can be determined. Once this factor is determined, it can be used for all subsequent work with any lens on the same camera body.

#### 5.2.1.3 Kodak DC40 or Compatible Camera

Recently, a large number of relatively low cost digital cameras have been developed. In contrast to the professional digital cameras which may cost $10k to $30k, these have prices in the range of $400 to $1000. The CCDs used by these cameras are much smaller than the CCDs used in the professional digital cameras. The small size of the CCDs requires new lenses with much shorter focal lengths than are used by 35mm film cameras. For example, in order to obtain an image equivalent to that produced by a 35mm film camera with a 50mm lens, a low cost digital camera must have a lens with a focal length of 7mm or less. As a result, not only are these cameras incapable of using standard 35mm camera lenses, but you would not want to use such lenses on these cameras even if you could.

Because of the need for new smaller lenses and the goal of reducing the prices of these cameras, these low-cost digital cameras do not offer interchangeable lenses. Each camera has a single fixed lens offering either a fixed focal length and field of view, or a choice of normal and telephoto settings. Wide angle options remain essentially nonexistent at this point in time, although this may change rapidly in the next few years as these cameras come into widespread use. The absence of any wide-angle options limits the ability to use these cameras for panoramic image capture, but they can still be used as long as one can tolerate a restricted vertical field of view.

Since these cameras do not accept interchangeable lenses, each product presents unique characteristics regarding focal length and field of view. In spite of this, all of these products tend to be very similar to each other and all have similar characteristics. Consequently, we have chosen one example, the Kodak DC40, as representative of this class, and have "hard-wired" the parameters for this particular camera. These same parameters may be close enough for other cameras of this type, or at least these parameters should provide a useful first approximation to to actual parameters of other similar cameras.

Someday, this program may offer a database of digital cameras so one may simply choose a particular make and model from a menu, but for now we must make do with the DC40 as the only choice.

#### 5.2.1.4 Other Camera Body Types

The "other" category is provided for any other type of camera body which does not fit the preceding categories. This may include large format film cameras (2.25x3.25, 4x5, 8x10, etc.) or other aspect ratios, such as square negatives (Hasselblad, etc.). Since these may be diverse, but used by professionals well-educated in optics and knowledgeable about how the focal length relates to the field of view, we simply give the user the responsibility of telling us either the 35mm equivalent focal length or the actual field of view of the images.

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### 5.2.2 Camera Orientation

The camera orientation specifies whether the field of view angle corresponds to the larger or smaller of the dimensions of a rectangular image. If the "portrait" option is selected, then the field of view angle will correspond to the smaller dimension. If the "landscape" option is selected, then the field of view will correspond to the larger dimension.

The panorama editor can determine how the camera was actually oriented for each image and will automatically apply the appropriate field of view independently of how the camera orientation is specified here. This choice is only needed to determine which field of view angle is indicated in the lens properties section.

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### 5.2.3 Lens Properties

The lens properties include the focal length, field of view angle, and barrel distortion value. In the case of a standard 35mm camera, the focal length of each lens is usually printed on the rim of the lens. If one has full negative prints, it should be possible to enter this value directly from the lens. If the images have been cropped so they do not represent 100% of the area of the original negative, or if any other type of camera has been used, one must enter the focal length of the equivalent 35mm lens providing the same field of view.

The field of view angle is really a combination of lens and body properties. This value is calculated and presented for the user's information in the Lens Properties section of the Camera Properties dialog. Alternatively, if the focal length of the camera is not known, but one can measure, estimate, or guess the field of view angle, then the field of view angle may be entered directly and the corresponding 35mm equivalent focal length will be calculated and presented in the focal length field.

Ideally, each lens is perfectly rectilinear and straight lines in the scene are represented by perfectly straight lines in the resulting images. Such results are expected from the ideal pin-hole cameras represented by the real cameras and lenses. Real lenses, however, may introduce distortions from these ideal conditions. The barrel distortion entry in the lens properties dialog allows the panorama editor to compensate for such distortions.

A non-zero value should be entered in the barrel distortion field only if the images show noticeable curvature of what should be straight lines. Such distortions, if any, will be most noticeable in areas most distant from the center of an image, and most pronounced in lines perpendicular to radial lines radiating from the center of an image. The value to be entered here should be determined by trial and error until all curvature appears to be removed from lines that should be straight.

Warning: The barrel distortion correction is very costly in terms of performance and should not be attempted until after refining all other parameters. In addition, this is an experimental correction and may be removed in subsequent versions of the panorama editor.

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### 5.2.4 Using the Camera Properties

After specifying the camera properties, the user has three options regarding what the panorama editor should do with these values. One choice, is the "Cancel" button which causes the information to be discarded and ignored. The same result is obtained for the "quit" button (X) in the title bar. Selecting the "OK" button stores the current settings where they will be applied to subsequently imported images. If the "Apply" button is selected, then the camera settings are applied retroactively to all previously imported images as well as to subsequently imported images.

The camera property settings have no effect on subsequent images specified in Raw Image Control Files. The side images specified in Raw Image Control Files have their own field of view angles which take priority over the values specified in the Camera Properties dialog. The Camera Properties dialog can be used to override the field of view settings specified in a Raw Image Control File by opening the Raw Image Control File first, then opening the Camera Properties dialog, and selecting the "Apply" button to apply the new camera properties to the previously opened images.

The camera properties have no effect on panoramic images or sprites.

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Last modified February 27, 1998.
wluken@watson.ibm.com