Digital Camcorders
Digital Camcorders |
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Richard H. Wiggins, III, MD has reported no financial interest, arrangement or affiliation with a commercial organization that may have a direct or indirect influence in the subject matter of this presentation.
Objectives
Introduction
With the advances of technology, the ability to have digital capabilities in a small package is now possible, bringing the abilities of the big movie studios to the lowly masses. The phrase "digital video" refers to the capturing, manipulation, and storage of motion images that can be displaced on a computer. In the older analog world, in order to display video images on a computer, the video signal had to first be converted from an analog to a digital format. Video digitalizing hardware on the computer had to be installed to do this conversion. To accomplish this required a high-end, powerful computer to be able to digitalize every frame of a video. Just like in radiology, where it makes more sense when you are capturing an image digitally, such as with CT and MRI, to then read the image digitally, with PACS, than to print out an analog version of the image you acquired digitally, it make more sense to acquire a video digitally and edit it digitally. Therefore, the entire process, including the capturing, editing, and displaying of video, is in a digital format.
This digital process begins with a camera and a microphone that captures the images and sounds of a video clip and send those analog signals (that exist as waves) to a video-capture adapter board. There is an analog-to-digital converter chip on this video-capture adapter card, which converts these analog signals into digital patterns (1's and 0's) and a compression/decompression chip (or software) reduces the amount of data needed to recreate the video and audio signals:
For those of you who like medical analogies, the lens of the camera is equivalent to the lens of the eye, focusing the image of interest. The Charged Couple Device (CCD) is like the retina, that the image is focused upon, and creates an analog RGB representation of the image focused upon it. The A/D converter, is then like the optic nerve, and then takes that analog image, and converts it to sampled digital values. The CCD interface (I/F) then sorts and buffers those digital sampled values, and sends them to the System Controller, that provides the system level interface of the hardware involved. The microcontroller (uC) assists with coordinating the interactions of the hardware and software in the system for the System Controller. The Image Processing is a hardware accelerator assistant provided to improve system level performance, and the Optional Digital Encoding assists with encoding the digital samples to MPEG (video) and JPEG (image). The controllers to the right of the image above perform interaction functions, to other digital or analog display devices (Digital Controller and Analog Controller), or memory resources and devices (Memory Controller), and nonvolatile secondary storage media (Storage Controller).
There are several attractive advantages to working in the digital environment. Comparing analog to digital in this sense is similar to comparing a typewriter to Microsoft Word. The current level of technology allows the user to use features like cut/copy/paste of the clipboard in editing digital video clips. There are many special features previously available to only large production studios that can now be available on a small digital camera. Current software for video editing now also allows the user to quickly organize video clips as well as edit sound separate from the video, and add a new soundtrack. Although major motion studio screen films are not digital (although this is changing; the latest Star Wars Prequel version was an all-digital production), they are still high quality analog images, but it is far easier to maintain digital video resolution then analog video. VHS type tapes are subject to video quality degradation much more than digital media. A digital video can be copied without losing its resolution; however, analog signals can experience resolution degradation, and will lose some quality with each reproduction and manipulation.
These digital video files can, however involve significant amounts of storage space. If a single image frame from a video with a spatial resolution of 640 X 480-pixels and a contrast resolution of 24-bits per pixel (True color) has a size of (640 X 480 X 24)/8 = 921,600 bytes, or 921 KB of data. So, if the clip has 30 frames per second that is 921 X 30 = 27.6 MB. If this clip is from a movie that is 1.5 hours long, or 90 minutes, or 5400 seconds, that is 27.6 X 5400 = 3812400 MB, or 3.8 TB of data without some kind of data compression! Obviously, compression is essential in working with digital video.
Similar to image file formats, there are two main types of video compression, lossy and lossless. The lossless type of compression retains the original data resolution, and decreases file size by removing redundant data. This compression rate is less than 4:1, so in the above example, it may only decrease the file size to 1 TB. The lossy compression algorithms decrease video and audio data that is less likely to significantly decrease resolution, while significantly decreasing file size. The most common video compression algorithms are AVI, MOV and MPEG.
AVI ("ay-vee-EYE") is an acronym for Audio/Video Interlaced, created by Microsoft to work with the Windows Operating System (OS). This format has several limitations, including compatibility problems with different operations systems and some hardware. The MOV ("EM-oh-vee") video file format, originally created by Macintosh, is the proprietary format of QuickTime, but can function on both Macintosh OS and Windows OS computers. MPEG ("EM-peg") is an acronym for the Moving Picture Experts Group and the digital video compression standards and video file formats developed by this group. This is actually a lossy compression algorithm, which has a significant compression rate by only saving information about the differences between frames, instead of all information required to create all of the images in each frame.
History
The history of digital video camcorders, itself is only about 10 years old, but it really began with the origins of similar technologies. In 1876, Alexander Graham Bell invented the telephone and brought a revolution in terms of electronic sound reproduction. This was expanded at the beginning of the 20th century with the radio (in about 1892) and the phonograph by Thomas Edison in 1877. Soon after, in about 1934, television demonstrated how analog technology could produce images and sound, using continuous electronic signal between a source and receiver.
In about 1950, the first computers were being created, but it wasn’t until the 1960s when the solid-state integrated circuits were invented that digital technology in computers exploded, leading to an impressive decrease in cost, and an increase in speed and stability. Some of these technologies were combined in the 1970s with the invention of the VCR. In the 1990s, HDTV was introduced as well as the technology leading to digital video. In the early 1990s, the VCR was an amazing product. Suddenly viewers were not dependent on viewing programs only when they were aired, they could be recorded and viewed at any time. It was another big step to the modern digital recording hard drives like the TiVo, and PVR available today, but the VCR was significant technology advancement.
In the late 1970s, the first portable video cameras emerged from JVC, and then models were released from Sony and RCA. These were big, bulky units using the VCR tapes found in the larger recorders and a separate, but connected camera. It wasn’t until 1982 that Sony and JVC produced combination devices called camcorders (Camera and Recorder: CAMera/reCORDER=CAMCORDER). JVC was pushing their small VHS standard for camcorders, VHS-C, while Sony was pushing their Beta standard camcorder. In 1984, Kodak introduced a new standard video format, the 8mm tape, and Sony released a 8mm tape camcorder the next year, and a higher resolution, Hi8 (high-band 8mm tape) three years later, in 1988.
JVC created an impressive and popular feature to the camcorder with the LCD screen in 1992, in addition to the traditional viewfinder. In 1995, Panasonic released the first MiniDV format cassettes. This allowed cameras to be smaller, and have higher resolution, fully twice the resolution of the VHS format.
Video Tape Formats
Video tape format types are usually divided into two categories: analog (VHS, VHS-C, 8mm, Hi8, S-VHS) and digital (MiniDV, Digital8). In general, the most significant difference is that analog camcorders record electronic video signals onto video tape as magnetic patterns on a continuous track. Digital camcorders take the same analog information and translate it into digital data, rather the storing the video signal as magnetic patterns.
Analog Formats:
VHS
VHS video camcorders use the same VHS tape that is used in videocassette recorders. Therefore, a user can simply remove the videotape out of your VHS video camera, and immediately insert the tape into a VCR for viewing. Because these camcorders use the larger size of videotape, they are larger and heavier than other camcorder formats, but were also more durable. The resolution of VHS tapes is about 200 lines.
VHS-C
A VHS-C video camera is about half of the size and weight of the VHS video camera, because the cassette that holds the tape is half the size of the VHS cassette. The "c" in the acronym is for "compact". These tapes use an adaptor to be able to play in a VCR. While they are much smaller, allowing the camera to be much smaller, they have a much shorter recording length, about 30 minutes.
8mm
The 8 millimeter (8mm) video tape format camera offers superior picture and sound quality compared to the VHS and the VHS-C formats. The 8mm tape is also smaller than the 1/2 inch size VHS-C tape. These tapes can not be viewed in a standard VCR. These tapes are a higher quality, but to play on a VCR, the user must copy the video onto a VCR tape. However, when this is done, the duplication causes degradation in quality, resulting in a resolution similar to VHS. These have a longer length of recording time, up to 120 minutes. 8mm was the smallest size format available, before the digital video units, with a resolution around 240 lines.
Hi8
The Hi8 tape is the size of an 8mm tape, but is higher quality. An 8mm tape can, however, be used in a Hi8 video camera. The Hi8 format tapes are otherwise similar to the 8mm tapes. This was the highest resolution available prior to digital video cameras, with a picture resolution of about 400 lines.
S-VHS
The "S" stands for "Super" in the acronym S-VHS, with superior images and sound, compared to the VHS tapes. These tapes added increased video and audio resolution, similar to the step-up from 8mm to Hi8 tapes. The S-VHS tapes have similar resolution to the Hi8 format tapes, about 400 lines. These were essentially the same size as the prior standard, and there was released an S-VHS-C version of tapes that could also be played in a VCR with an adaptor.
Digital Formats:
MiniDV
MiniDV is the most common of the digital formats, and is the smallest of all formats, making the camcorders smaller than any other format. MiniDV tapes record video in a compressed, digital format on a small, 60-minute length tape. The MiniDV tape is about 1/10 the size of a VHS tape and its resolution is 500 lines.
Digital8
The
Digital8 format is the digital equivalent of the Hi8 tape format.
The characteristics and resolution are similar to those of the MiniDV camcorders, except that the Digital8 video camcorder can play 8mm and Hi8 tapes, therefore making this an attractive option to users who owned those types of camcorders previously and are considering upgrading to digital. Therefore, the camera is using the same tapes, but storing data on them differently. Because the amount of digital data occupies more space, a 120-minute analog Hi8 tape will only store 60 minutes of digital video data.
Pricing
The first consideration of what kind of camera to purchase is whether you should invest in a digital (Digital8, MiniDV) or analog (VHS, 8mm, Hi8, VHS-C, S-VHS-C) formatted camera. One of the biggest limitations for some users with these formats is cost. In general, you will get twice the quality of video by using digital instead of an analog VHS format. The ability to edit digital video on a computer is far easier if you have a digital camera, and will be worth the extra cost up front in purchasing the device. Digital video cameras have a price range roughly from $400 to $2000. There are fortunately many different types of digital video cameras available in this range, and features like optical and digital zoom make the differences in cost.
Lens
The lens is the
equivalent of the eye of the camera. Just like us, some cameras see well,
and others don’t see quite so well. The quality of the lens is one of
the considerations when considering a digital camcorder purchase. Almost
all digital camcorders will offer both optical and digital zoom. The
optical zoom is the more important of the two. The lens is made up of two
glass lenses, and the distance between the two creates the zoom ratio of
the camera. The optical zoom is creating magnification based on the optics
of these glass lenses, and therefore does not effect the video resolution
of the camera. The digital zoom is simply a digital enlargement of the
image that passes through the glass lenses to the CCD. Each increase in
digital zoom causes a decrease in resolution.
A 10-12X optical zoom is good and will usually be sufficient for most video projects. Cameras have been advertised with digital zoom ratios up to 700X. This is WORTHLESS. Do not be fooled by this. Some camera manufacturers are known for good optics for the optical zoom (glass lenses optics) and this is much more important than the digital zoom capabilities.
CCD
If the lens is like your eye, then a CCD is like your retina and optic nerve. The Charge Coupled Device (CCD) is the name of the computer chip inside the camera that actually acquires the light and color through the lens, converting it into a digital signal. Lower cost cameras have 1 CCD, and more expensive units have 3 CCDs. Usually the 3 CCD cameras are reserved for video professionals in broadcasting, not parents filming first steps.
Viewfinders and LCD screens
The
viewfinder is the eyepiece on the back of the camera that you can look into
to see what the camera is pointed at, and is usually in black and white.
The Liquid Crystal Display (LCD) screen is the foldout screen on the side
of the camera used to see what you are shooting, usually in color. Larger
LCD screens (up to 4”) are generally more expensive, but 3”
screens are usually adequate. The LCD will use up battery power much faster
than just using the viewfinder.
Connections
Most digital cameras come with either USB 1.1 or FireWire (IEEE 1394) network capabilities to transfer the video to a computer. While all modern Macintosh computers have native FireWire (developed by Macintosh), not all Windows OS machines have FireWire capabilities, so you may be forced to invest in a FireWire card (under $100.00). USB 1.1 has a theoretical network speed of 12 MB per second, while FireWire has a theoretical speed of 50 MB per second. As explained earlier, digital movie files are enormous, thus FireWire is the recommended connectivity for efficient transfer to your desktop for editing.
Digital Camcorder Features
Image stabilization
Since most folks are going to hand hold their camera, image stabilization is important to reduce jiggling. There are two types: optical and digital. Optical systems produce a smoother look, and will cost you more. They use little gyroscopes within the lens system of the camera to steady the image. Digital stabilizers use an electronic circuit and software to do much the same thing, but can introduce some weird artifacts in your image. Look for an option to turn it off for the best possible image quality.
Special effects
Some cameras have special effects built right into the camera. These include strobe, old-fashioned movie, monochrome, and transitions, and special pre-sets for specific lighting.
Audio
Most cameras have a built-in microphone that works pretty well, although usually only capturing the sound in an arc beginning with the user and projected directly in front of the camera. If one desires a higher quality audio track, most cameras also come with an external microphone port. When recording outdoors, it is important to use the “Wind Cut” option, which helps reduce the (sometimes very loud and annoying) artifacts caused by wind hitting the microphone sensor. If this isn’t an option on your camera, or if it isn’t working well enough, you can always attach an external microphone with a wind cover (like your local newscasters use).
Manual controls
Point and shoot means all you have to do is know how to start the tape rolling, operate the zoom, compose a shot, and hold the camera fairly steady.
Battery life
Obviously an important issue, unless you plan to be plugged into the AC all the time. Check how long the battery will run while recording. Some cameras now claim to run 4 or 8 hours.
Video Capture Tips
Try to always use a tripod
The tripod ensures increased stability, thus avoiding the “Blair Witch” jumping images, which scared directors everywhere.
Turn off the date and time text
Try to avoid using the text stamping features on the video camera. Most of this can be added later with editing software easily, and you may want to use the clip without it in the future. It is easier to add than remove. If you really think you want it on, have it display when you start, and then remove it.
Avoid using the digital zoom
There are cameras that advertise 700 X digital zoom in big letters. Chances are that will be amazingly useless to you. Optical zoom is nice, but digital zoom is actually next to worthless, especially at 700X. Try opening an image in PhotoShop and then zooming in to 700X, you will see what I mean.
Pan slowly
Try to pan slowly and smoothly. You look silly doing it, but that fast, jerky motion is wasted tape, the image will almost always be completely blurred out and unusable with fast pans.
Maximize light
It may look too bright when you are taping, but usually it will look better when looking at the digital feed from the camera. Also try not to mix light sources, such as strong sunlight and strong fluorescent lights both pointing at the subject.
Be quiet
If the camera you are using has a microphone on it that you are using, the level of audio from the user of the camera will be amazingly higher than the subject. If you are video taping a subject several feet away, you will likely turn up the audio when viewing the video later, causing the user of the video to always sound like they are SCREAMING. Also, don’t forget to activate Wind Cut.
Try to always use the high quality tape at normal speed (SP)
The cost of tape media is relatively low, and there may be a noticeable difference with low quality tape media, and the difference between normal speed (SP) recording and extended slow (ESP) recording can be obvious.
Digital Video Resources
Copyright © 2004 American Society of Neuroradiology, www.asnr.org