- Automatic vertical keystone correction technology instantly projects a square image even when the projector is set up at a steep offset angle to the screen; Auto power-on via the RGB (15-pin) input connector when a signal is detected from a computer; Sleep timer can be set to automatically turn off the projector at set countdown times.
- The keystone effect is often a curse faced by many people using screen projectors or when taking photographs from certain angles. The keystone effect or keystone projection can be corrected using various types of methods, using manual and digital correction option.
In these cases the projector keystone correction is generally insufficient and the perspective warping needs to be done via software. Projection Mapper basically reads the primary screen buffer and allows you to project it and correct the perspective via software on a secondary monitor. Download Projection Mapper directly from here.
Image warping (geometric correction) is used to make an image look visually correct when it is projected onto a non-planar screen.
Image warping (geometric correction) is used to make an image look visually correct when it is projected onto a non-planar screen. This process is also referred to as distortion correction or geometric correction. The image is warped so when it is projected onto the screen it is visually correct.
Forms of image warping can be found in many projector models, with a function known as keystone correction being the most common. Keystone correction (trapezoidal in nature) is used when projectors have been mounted at an angle (generally pointing down from a ceiling to a screen), and the opposing angular correction needs to be applied in order for the image to be correct. Whilst most current projectors offer this feature, in many areas, advanced functions are required. For example, advanced off-axis correction and projection on curved and other unusual surfaces. For these applications, geometric correction tools such as ImmersaView Warp can be used.
Areas where geometric correction is required include:
![Correction Correction](https://shopitjamaica.com/wp-content/uploads/2020/08/EAA64DED-AAF6-421C-95E3-64937ACECECE-600x469.jpg)
- Advanced off-axis correction where projector placement is awkward and needs an advanced mapping over the keystone function in a projector
- Non-planar screens such a curved screens and hemispherical domes
- Projecting one image from one projector onto more than one surface
- Unusual projection applications onto custom designed screens
![Software Software](https://i.ytimg.com/vi/3ZSd5qlgHMA/hqdefault.jpg)
Figure 3: An example of an advanced off-axis correction.
Figure 4: An example of spherical correction.
Projector Keystone Correction Software Mac
To describe the process of geometric correction in greater detail, we have taken the example of projecting onto a curved surface. For cylindrical and spherical screens, variations of barrel and pincushion correction functions are required to correct the image. The exact mapping will be dependent upon the optical characteristics of the projector, the screen’s size and shape as well as whether the imagery is front or rear projected.
Geometric correction can be performed with some special high-end projectors with advanced modules, but they are not common and tend to be expensive. There are also external electronic devices which can compensate for any geometric correction, but these also tend to be expensive.
Recently with advances in computer graphics cards, software solutions can now offer the ability to perform geometric correction. One such tool is ImmersaView Warp. This method provides a user with a number of control points which can be increased/decreased depending upon the complexity of the screen shape (see Figure 5). These control points can be manipulated by the user so an image is aligned correctly to a screen.
Figure 5: Control points for included for image warping.Typically, when a standard projector is used on a curved (cylindrical) screen, the image gets a characteristic “smile” shape (see Figure 6). To overcome this we need to use the control points along the top and bottom of the image to pull the image back down into shape. Because the pixels in the middle of the image will be bigger than the pixels at the edges, we compensate for this by dragging the control points near the center of the screen closer together. This tells the software system that these parts of the screen are further away and it automatically adjusts. ImmersaView Warp displays a checkerboard, which helps to create the right image warping pattern. When all the checks in the checkerboard look the same size, the distortion correction is correct.
Figure 6: Characteristic smile distortion when projecting onto a cylindrical screen.There are also other screen shapes that can be produced from complex curved and flat sections. One example of a linear based display is a wedge, composed from two flat screens. Here a single projector can be used with two advanced keystone correction patterns to project onto a single screen. Figure 7 shows an example of the pattern needed to rear project onto a convex wedge screen. To create these shapes the distortion systems need to be told that they are dealing with flat sections and rather than curved screens.
Figure 7: Projection map onto a two linear screens from one projector.Download Resource
The projected image has been keystone-corrected to be rectangular.
Projector With Horizontal Keystone Correction
The projected image has not been keystone-corrected to be rectangular.
The keystone effect is the apparent distortion of an image caused by projecting it onto an angled surface. It is the distortion of the image dimensions, such as making a square look like a trapezoid, the shape of an architectural keystone, hence the name of the feature. In the typical case of a projector sitting on a table, and looking upwards to the screen, the image is larger at the top than on the bottom. Some areas of the screen may not be focused correctly as the projector lens is focused at the average distance only.
In photography, the term is used to describe the apparent leaning of buildings towards the vertical centerline of the photo when shooting upwards, a common effect in Architectural photography. Likewise, when taking photos looking down, e.g., from a skyscraper, buildings appear to get broader towards the top. The effect is usually corrected for by either using special lenses in Tilt–shift photography or in post-processing using modern image editing software.
Brooklyn Bridge keystoning
Theory[edit]
The distortion suffered by the image depends on the angle of the projector to the screen, and the beam angle.
The distortion[clarification needed] (on a two-dimensional model[clarification needed], and for small focus angles) is best approximated by:
where is the angle between the screen axis[clarification needed] and the central ray from the projector, and is the width of the focus[clarification needed].
From the formula, it is clear[clarification needed] that there will be no distortion when is zero, or perpendicular to the screen.[citation needed]
Keystone effect in stereo imaging[edit]
In stereo imaging, two lenses are used to view the same subject image, each from a slightly different perspective, allowing a three-dimensional view of the subject. If the two images are not exactly parallel, this causes a keystone effect. This is particularly noticeable when the lenses are close to the subject, as with a stereo microscope,[1] but is also a common problem with many 3D stereo camera lenses.
Solving the problem[edit]
The problem arises for screen projectors that don't have the depth of focus necessary to keep all lines (from top to bottom) focused at the same time. Common solutions to this problem are:
- moving the projector more to the center of the screen,
- tilting the screen in a small angle,
- the use of special software on the projector
- and computer controlling the projector.
Correction[edit]
Keystone correction, colloquially also called keystoning, is a function that allows multimedia projectors that are not placed perpendicular to the horizontal centerline of the screen (too high or too low) to skew the output image, thereby making it rectangular.
It is often necessary for a projector to be placed in a position outside the line perpendicular to the screen and going through the screen's center, for example, when the projector is mounted to a ceiling or placed on a table top that is lower or higher than the projection screen. Most ceiling-mounted projectors have to be mounted upside down to accommodate for the throw of the image from the lens, with the image rotated right-side-up with software. Keystone correction is a feature included with many projectors that provides the ability to intentionally 'distort' the output image to recreate the original rectangular image provided by the video or computer source, thus eliminating the skewed output that would otherwise result due to angled projection.
The ability to correct horizontal keystone distortion is generally only available on larger or professional level projectors. In most consumer units, this is easily corrected by moving the projector left or right as necessary, or less often by lens shifting, with similar principles as Tilt–shift photography.
Functionality[edit]
In modern projectors keystone correction technology is performed digitally (rather than optically) via the internal (LCD) panels or (DLP) mirrors of the projector, depending on the technology used. Thus, when applying keystone correction to an image, the number of individual pixels used is reduced, lowering the resolution and thus degrading the quality of the image projected. Home theater enthusiasts would argue that keystoning should not be used because of the impact it has on image quality. However, it is a useful technology in cases where the projector cannot be mounted directly in front of the screen, or on projectors utilizing lens shift technology where the projector must be mounted outside the frame of the screen.
See also[edit]
References[edit]
- ^Introduction to stereo microscopy
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