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Topics covered:
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 What is HDTV?
Which HDTV versions exist?
What is HD ready?
What is Resolution?
What is Aspect Ratio?
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What is HDTV?
HDTV (High Definition Television) is a designated future television standard offering much more digital information than today’s „Standard Definition“ television systems PAL and NTSC respectively. Consequently, HD images on a screen consist of more and more tightly packed pixels and offer a much higher resolution. Stated simply, High Definition means better looking pictures that bring you a step closer to reality.
HDTV originates from the broadcast sector, but beside the use in the consumer market HDTV also provides a much more detailed, sharper and realistic impression in medical applications.
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Which HDTV versions exist?
Two main HDTV standards are currently used: HDTV1080i and HDTV720p. The number stands for the quantity of horizontal lines that comprises the image on the screen, while the letter stands for the scan mode: Interlaced or progressive. Interlaced scan is a technique of reducing the data volume without significantly compromising on image quality. It initially scans only every second line of an image, then in a second scan draws in the gaps between the lines of the previous scan. Progressive scan draws the image sequentially line by line, from top to bottom.
Both standards have their advantages and disadvantages and the decision for either one can best be based on what type of content the imaging modality is used for. Based on decades of experience in endoscopic imaging technology, Olympus decided for HDTV1080i in EXERA II to accomplish the best image quality currently possible.
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What is HD ready?
“HD ready” is a logo that shows if display equipment is capable of processing and displaying high-definition signals. It is primarily designed for home cinema systems and does not relate to imaging platforms.
The fact that a screen bears the label „HD ready“ does not necessarily mean that it has 1080 scanning lines. Many HD ready monitors simply interpolate 1080i resolution to 720 lines.
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What is Resolution?
Image resolution describes the detail an image holds. Basically, it quantifies how close structures can be to each other and still be visibly apart. An established measuring unit regarding digital images resolution is the number of pixels (short for picture element, using the common abbreviation “pix” for picture) that make up the image. Pixel counts can be expressed as a single number, as in a “three megapixel” digital camera, which nominally has three million pixels or a pair of numbers, as in a “640 by 480” VGA computer display, which has 640 pixels from side to side and 480 from top to bottom. Another way is to only specify the vertical resolution by indicating the number of pixel lines, like in HDTV1080i which has 1080 pixels from top to bottom. As a comparison, PAL has only 576 visible lines and NTSC even only 480.
The more pixels used to represent an image, the closer the result can resemble the original: Increasing the number of pixel lines obviously increases the quality of the picture and subsequently provides the surgeon with a more detailed and realistic impression.
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What is Aspect Ratio?
The aspect ratio of an image is its displayed width divided by its height. For instance, the aspect ratio of a traditional television screen is 4:3 which means the image is a little bit wider than high. This aspect ratio has been in use since television‘s origins and many computer monitors also use it.
When cinema attendance dropped, Hollywood created widescreen aspect ratios to immerse the viewers at movie theatres and provide a more realistic experience. As a consequence, these films, watched on regular TVs have masked-off areas above and below the picture area (often referred to as „black bars“). Wide screen TV sets with a 16:9 aspect ratio follow this trend and allow motion-pictures to be viewed without “black bars”.
Present technology does not allow for effective pixel use at a 16:9 aspect ratio in endoscopy because of restrictions imposed by the round shape of the endoscope. The below drawings visualise the limitations: a 16:9 shaped CCD would not be the best choice for optimum coverage of the round area inside an endoscope (1,2). Only the endoscopists can decide whether the blue (on top and bottom) or the red (left and right) area is more important to be visualised (4). Fact is, the blue area in the right drawing (4) is 14.5% bigger than the red area, which means a 5:4 ratio provides higher resolution. a 5:4 shaped CCD is very near to the ideal square shape (1). Electronic conversion to a 16:9 image would result in loss of information (image cut off (2) or electronic zoom (3)). The Olympus-preferred aspect ratio (5:4) produces the best HD image by delivering a depiction with the highest resolution and pixel density currently available.
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