Document camera

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Document cameras, also known as visual presenters, visualizers, digital overheads, or docucams, are high-resolution real-time image capture devices used to display an object to a large audience, such as in a classroom or a lecture hall. They can also serve as replacements for image scanners. Similar to opaque projectors, document cameras can magnify and project the images of actual, three-dimensional objects, as well as transparencies.^[1]

To operate a document camera, a webcam is mounted on arms, allowing them to be positioned over a page. The camera connects to a projector or similar video streaming system, enabling a presenter to write on a sheet of paper or display a two- or three-dimensional object while the audience watches. Larger objects, for instance, can be positioned in front of the camera, which can then be rotated as needed. Alternatively, a ceiling-mounted document camera can create a larger working area.

Typical uses include:

• In a lecture hall or classroom
• Presentation of material in conferences, meetings, and training sessions
• Videoconferencing and telepresence
• Presentation of evidence in courtrooms
• Various medical applications (telemedicine, telepathology, display of radiology images)

Document cameras replaced epidiascopes and overhead projectors, which were formerly used for this purpose. By means of the zoom feature, a document camera can enlarge the small print in books and project a printed page as if it were a traditional transparency. Document cameras do not require the lights to be dimmed in the room they are used in, contrary to what overhead projectors require to be visible.^[1] Most document cameras can also send a video signal to a computer via a USB cable. Sometimes document cameras are connected to an interactive whiteboard instead of a standard screen.

Document cameras were developed to meet increased demand for the ability to project and present original documents, plans, drawings, and objects directly rather than necessitating the prior preparation required for their use as part of an overhead projector-based presentation. The first Visualizer/Document camera was developed by the companies WolfVision and Elmo and was launched at the Photokina Trade Fair in 1988.^[2][3]

The widespread use of computers, projectors, and popular presentation programs such as Microsoft PowerPoint in meeting rooms meant that overhead projectors became less frequently used.

The first attempts and prototypes were mostly simple video cameras on a copystand. During the mid-1970s, these were assembled and equipped with additional lighting to provide a consistent quality of the projected image, as well as enable use in a darkened room.

Toward the end of the 1990s, progressive scan cameras were introduced. Many visualizers available on the market today are capable of an output of at least 30 frames per second.

The design and specification of a document camera are a combination of several different technologies. The quality of the recorded image is dependent on the primary components, which are: optics, camera, lighting system, and motherboard with appropriate firmware (software). The finished product is then realized by the production of different mechanical designs by individual manufacturers. Some document cameras offer HDMI output, audio/video recording, and Wi-Fi connectivity.

Optics are one of the most critical components relating to image quality, and the quality of the optical system used will largely depend on the planned cost of the device. Simple or highly complex optical systems can be used, which can differ significantly in quality and size. The iris or aperture is another important component of the optics. The iris controls and regulates the amount of light that passes through the lens onto the image sensor. A lens will focus on exactly one point of an object to be imaged onto the sensor. However, there is also an area in front of and behind the point of focus that will be perceived as being in sharp focus by the human eye. This is called the depth of field, and it is dependent upon the size of the iris or aperture. The smaller the aperture, the greater the depth of field.

Progressive scan cameras use either CCD sensors or CMOS sensors. The general advantage of progressive scanning over the interlaced method is the much higher resolution. A progressive scan camera captures all scan lines at the same time, whereas an interlaced camera uses alternating sets of lines.

Image sensors provide only monochrome images. With a 1-chip camera, color information can be obtained through the use of color filters over each pixel. With 1-chip cameras, the Bayer filter is very commonly used. Red, green and blue filters are arranged in a pattern, where the number of green pixels is twice as large as that of the blue or red; thus, the higher sensitivity and resolution of the human eye is replicated. To get a color image, different algorithms are then used to interpolate the missing color information.

A 3CCD camera module is another way to produce color images. A prism is used to split white light into its red, green, blue components, and a separate sensor is then used for each color. This complex camera technology is used in 3-chip cameras and allows for excellent color reproduction at very high resolutions.

Modern camera systems used in a document camera are able to provide high-resolution color images at 30 frames per second. In a 3-chip camera, the measured resolution may be up to 1500 lines. In addition, the image can be adapted to fit common display aspect ratios of 4:3, 16:9, and 16:10.

Lighting is an essential part of a document camera. To ensure good color rendition, the lighting system to illuminate the image capture area should be uniform.

• The greater the light intensity, the more independent the document camera is from ambient light sources.
• Using powerful lighting systems enables smaller apertures to be used, and this, in turn, provides a significant increase in the depth of field that can be achieved by the document camera.
• Also, the higher the quality of the light source, the more light will reach the camera sensor, which results in less noticeable noise; therefore, the quality of the image will not be degraded.

Some document camera models integrate additional functionality into the light system, such as a synchronized light field that indicates to the user at all times, by way of an illuminated image capture area or laser markers, the size and position of the imaging area, which adjusts simultaneously as the lens zooms in or out.

The motherboard plays an important role in image processing and it has a major influence on the quality of the eventual image that is produced. Larger and larger resolutions and high refresh rates generate large amounts of data that must be processed in real time.

Document cameras have various sophisticated automated systems designed to make the user experience as easy as possible. Permanent autofocus detection, for example, automatically adjusts the focus settings when a new object is displayed, with no need for user intervention. Other important features include automatic auto iris, auto exposure, white balance, and automatic control gain.

Modern motherboards have a variety of connections to ensure flexibility of use. In addition to HDMI, DVI and VGA ports for connecting to displays, (projectors, monitors and video conferencing systems) there are also several interfaces provided to facilitate connection to a computer or interactive whiteboard. These interfaces are most commonly USB, Network (LAN) and serial.

In addition, an external PC or laptop can be connected to the document camera to allow for switching between a Power Point presentation and a live demonstration. Some models can also handle external storage devices and play files directly from a USB flash drive, or save images taken during the presentation onto it.

Some document camera manufacturers also provide for regular firmware upgrades.

Document cameras are generally divided into three groups:

• Portable: Smaller and lightweight models.
• Desktop: Larger, sturdier and more stable units.
• Visualizers: Ceiling-mounted above a tabletop or podium.

Portable and desktop models allow a working environment similar to an overhead projector. Many document camera users appreciate the added flexibility regarding the variety of objects that can be displayed to an audience. Portable devices can be used in multiple locations without requiring any prior installation.

Ceiling-mounted document cameras/visualizers are a variation from the traditional desktop models and allow for larger objects to be displayed. There is no desktop technical equipment to restrict the views of the speaker and audience, as the technology is installed unobtrusively in the ceiling. Ceiling models are often used to support videoconferencing or telepresence systems to further enhance the immersive experience for participants. ^{[4] [5]}

Document cameras have also been used as replacements for image scanners.^[6] Capturing images on document cameras differs from that of flatbed and automatic document feeder scanners in that there are no moving parts required to scan the object. Conventionally either the illumination/reflector rod inside the scanner must be moved over the document (such as for a flatbed scanner), or the document must be passed over the rod (such as for feeder scanners) in order to produce a scan of a whole image. Document cameras capture the whole document or object in one step, usually instantly. Typically, documents are placed on a flat surface, usually the office desk, underneath the capture area of the document camera. The process of whole-surface-at-once capturing has the benefit of increasing reaction time for the workflow of scanning. After being captured, the images are usually processed through software that may enhance the image and perform such tasks like automatically rotating, cropping, and straightening them.^[7]

The documents or objects being scanned are not required to make contact with the document camera, increasing the flexibility of the types of documents that can be checked. Objects that have previously been difficult to scan on conventional scanners can now do so with one device. This includes, in particular, documents of varying sizes and shapes, stapled, in folders, bent, or crumpled, which may get jammed in a feed scanner. Other objects include books, magazines, receipts, letters, tickets, etc. No moving parts can also remove the need for maintenance, a consideration in the total cost of ownership, which includes the continuing operational costs of scanners.

Increased reaction time whilst scanning also has benefits in the realm of context-scanning. ADF scanners, whilst very fast and very good at batch scanning, also require pre and post-processing of the documents. Document cameras can be integrated directly into a workflow or process, for example, a teller at a bank. The document is scanned directly in the context of the customer, in which it is to be placed or used. Reaction time is an advantage in these situations. Document cameras usually also require a small amount of space and are often portable.^[8]

While scanning with document cameras may have a quick reaction time, large batch scanning of even and unstapled documents is more efficient with an ADF scanner. This kind of technology faces challenges regarding external factors (such as lighting) that may influence the scan results. How these issues are resolved firmly depends on the sophistication of the product and how it deals with these issues.

• Planetary scanner