# Document camera

Document cameras, also known as visual presenters, visualizers, digital overheads, docucams, or simply doc-cams, 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.
A webcam is mounted on arms to operate a document camera, allowing it to be positioned over a page. The camera connects to a projector or similar video display 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.

## Use cases

Document cameras are commonly used in:
* Lecture halls or classrooms
* 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 overhead projectors, which were formerly used for this purpose. A document camera can enlarge the small print in books and project a printed page as if it were a traditional transparency by using a zoom feature. Document cameras do not require the lights to be dimmed in the room they are used in, contrary to what overhead projectors need to be visible. Most document cameras can also send a video signal to a computer.

## History

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 document camera, known as a visualizer, was developed by Wolf Vision and Elmo and launched at the Photokina trade fair in 1988.
The widespread use of computers, projectors, and popular presentation programs such as Microsoft PowerPoint in meeting rooms led to overhead projectors being used less frequently.
Early prototypes were simple video cameras mounted on copy stands. During the mid-1970s, these were assembled and equipped with additional lighting to provide a consistent quality of the projected image and enable use in a darkened room.
Progressive scan cameras were introduced toward the end of the 1990s. The modern visualizers available on the market can output at least 30 frames per second.

## Technology

The design and specification of a document camera combine several different technologies. Image quality depends on primary components: optics, camera, lighting, and the motherboard, which must have the appropriate firmware. Individual manufacturers produce different mechanical designs and then realize the finished product. Some document cameras offer HDMI output, audio/video recording, and Wi-Fi connectivity.

### Optics

Optics are critical to image quality and vary based on the device's cost. Optical systems can differ significantly in quality and size based on their complexity. The iris, or aperture, is a critical component of the optical system. The aperture controls and regulates the amount of light that passes through the camera lens onto the image sensor. The lens then focuses on a single point of the object, projecting it onto the sensor. The area in front of and behind the point of focus is called the depth of field and affects how much of the image will be perceived as being in focus by the human eye. Depth of field depends upon the size of the aperture: the smaller the aperture, the greater the depth of field.

### Camera

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. 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. Because of this, the filter is better adaptable to the higher sensitivity and resolution of the human eye. 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, and blue components, and a separate sensor is then used for each color. This camera technology 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 1,500 lines. In addition, the image can be adapted to fit common display aspect ratios of 4:3, 16:9, and 16:10.

### Lighting system

A uniform lighting system is essential for accurate color rendition in document cameras.
* High-intensity lighting permits the document camera to produce clear images regardless of ambient light conditions.
* Utilization of powerful lighting systems enables smaller apertures to be used, and this, in turn, can provide an increase in the depth of field that can be achieved by the document camera.
* If the quality of the light source is increased, more light can reach the camera sensor, which results in less noticeable noise, permitting the quality of the image to 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.

### Motherboard and firmware

The motherboard plays an important role in image processing and it has influence on the quality of the eventual image that is produced. Larger resolutions and high refresh rates generate large amounts of data that must be processed in real time.
Document cameras can be equipped with a range of advanced automated systems designed to enhance ease of use and improve functionality and image quality. For instance, permanent auto-focus detection automatically adjusts focus settings whenever a new object is displayed, eliminating the need for manual adjustments. Other examples of automated features include automatic iris adjustment, auto exposure, white balance, and automatic gain control.
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 camera types

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

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 models

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.

### Document camera scanners

Document cameras have also been used as replacements for image scanners. 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.
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 require a small amount of space and are often portable.

## Drawbacks

While scanning large batches of un-stapled documents, ADF scanners can be more efficient when compared to these cameras. These cameras may face challenges with certain environmental conditions such as poor lighting, which may decrease the quality of scanned documents.