|
| Home > Photo, Video, Graphics > graphics > |
| AVI Graphics Format Overview |
Section 13 of 14 - Prev - Next
All sections - 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13 - 14
The Intel Architecture is a de facto standard. Intel has repeatedly added new instructions and features to the architecture, although so far maintaining backward compatibility with previous versions. New instructions such as the MMX instructions and the Streaming SIMD Extensions in the Pentium III can be used to accelerate video codecs such as are used in AVI files. Advanced Micro Devices (AMD), National Semiconductor's Cyrix division, and Integrated Device Technology (IDT) manufacture processor chips compatible with the Intel Architecture.
As a rough rule of thumb, an image with a PSNR of 25 dB (decibels) is usually pretty poor. Anything below 25 dB is usually unacceptable. Perceived quality usually improves from 25 dB to about 30 dB. Above around 30 dB images look pretty good and are often indistinguishable from the uncompressed original image.
The human visual system appears to have sensitivity thresholds. This can be rigorously demonstrated in controlled experiments using sinusoidal gratings against black backgrounds. Because of this thresholding, once the PSNR exceeds some value, the errors become undetectable to human viewers. Hence an image with a PSNR of 35 dB may look the same as an image with a PSNR of 40 dB.
Conversely, the human visual system seems to have a saturation effect as well. Once the image quality falls below a certain level, the image simply looks bad. An image with a PSNR of 15 dB and an image with a PSNR of 10 dB may look equally bad to a viewer. Typically by this point the image appears quite poor.
There is a range where the perceived quality and the PSNR tend to scale.
| ************ Q| ***** u| **** a| *** l| ** i| ** t| *** y|********** | --------------------------------------------- 25 dB 30 db 35 dB (PSNR) Relationship Between Perceived Quality and Image PSNR
The Mean Squared Error is the mean of the squares of the differences between the values of pixels in two images. If i and j are indices of an images and N is the total number of pixels:
MSE = (1 / N) * (Sum[i][j] |P[i][j] - Q[i][j]|^2
Where P and Q are two images. i and j are the horizontal and vertical location of a pixel. P[i][j] is the value of the pixel at location (i,j) in the image. Sum[i][j] indicates a sum over i and j.
The Root Mean Squared Error (RMSE) is:
RMSE = Sqrt(MSE)
The Peak Signal to Noise Ratio expressed in decibels is:
PSNR = 20 log_10(b/RMSE)
Where b is the peak value for a pixel, typically 255 (8 bit pixels).
The ISO (International Organization for Standardization) gives the following definition: "Standards are documented agreements containing technical specifications or other precise criteria to be used consistently as rules, guidelines, or definitions of characteristics, to ensure that materials, products, processes and services are fit for their purpose."
Standard can have a precise legal meaning in the context of U.S. law, the laws of foreign nations, treaties and international organizations such as the United Nations. For example, the United States Office of Management and Budget (OMB) Circular A-119, "Federal Participation in the Development and Use of Voluntary Consensus Standards and in Conformity Assessment Activities", Revised and Dated February 10, 1998 provides the following definition of standards (Note: the Act refers to Public Law 104-113, the "National Technology Transfer and Advancement Act of 1995"):
WHAT DEFINITIONS OF STANDARDS
3. What Is A Standard?
a. The term "standard," or "technical standard" as cited in the Act, includes all of the following:
(1) Common and repeated use of rules, conditions,guidelines or characteristics for products or related processes and production methods, and related management systems practices.
(2) The definition of terms; classification of components; delineation of procedures; specification of dimensions, materials, performance, designs, or operations; measurement of quality and quantity in describing materials, processes, products, systems, services, or practices; test methods and sampling procedures; or descriptions of fit and measurements of size or strength.
b. The term "standard" does not include the following:
(1) Professional standards of personal conduct.
(2) Institutional codes of ethics.
c. "Performance standard" is a standard as defined above that states requirements in terms of required results with criteria for verifying compliance but without stating the methods for achieving required results. A performance standard may define the functional requirements for the item, operational requirements, and/or interface and interchangeability characteristics. A performance standard may be viewed in juxtaposition to a prescriptive standard which may specify design requirements, such as materials to be used, how a requirement is to be achieved, or how an item is to be fabricated or constructed.
d. "Non-government standard" is a standard as defined above that is in the form of a standardization document developed by a private sector association, organization or technical society which plans, develops, establishes or coordinates standards, specifications, handbooks, or related documents.
4. What Are Voluntary, Consensus Standards?
a. For purposes of this policy, "voluntary consensus standards" are standards developed or adopted by voluntary consensus standards bodies, both domestic and international. These standards include provisions requiring that owners of relevant intellectual property have agreed to make that intellectual property available on a non-discriminatory, royalty-free or reasonable royalty basis to all interested parties. For purposes of this Circular, "technical standards that are developed or adopted by voluntary consensus standard bodies" is an equivalent term.
(1) "Voluntary consensus standards bodies" are domestic or international organizations which plan, develop, establish, or coordinate voluntary consensus standards using agreed-upon procedures. For purposes of this Circular, "voluntary, private sector, consensus standards bodies," as cited in Act, is an equivalent term. The Act and the Circular encourage the participation of federal representatives in these bodies to increase the likelihood that the standards they develop will meet both public and private sector needs. A voluntary consensus standards body is defined by the following attributes:
(i) Openness.
(ii) Balance of interest.
(iii) Due process.
(vi) An appeals process.
(v) Consensus, which is defined as general agreement, but not necessarily unanimity, and includes a process for attempting to resolve objections by interested parties, as long as all comments have been fairly considered, each objector is advised of the disposition of his or her objection(s) and the reasons why, and the consensus body members are given an opportunity to change their votes after reviewing the comments.
b. Other types of standards, which are distinct from voluntary consensus standards, are the following:
(1) "Non-consensus standards," "Industry standards," "Company standards," or "de facto standards," which are developed in the private sector but not in the full consensus process.
(2) "Government-unique standards," which are developed by the government for its own uses.
(3) Standards mandated by law, such as those contained in the United States Pharmacopeia and the National Formulary, as referenced in 21 U.S.C. 351.
The AVI file format is an example of a standard. AVI would probably be considered a "de facto standard" in the language of the U.S. Federal Government.
Under the Uruguay Round agreements that established the WTO, the United States was able to exempt government sponsored research and development of non-commercial working prototypes from treatment as a government subsidy to industry. While the United States has relatively few direct subsidies of companies compared to other nations, many high technology businesses in the United States were built on technologies and non-commercial working prototypes developed with federal funding. The Internet and the Worldwide Web are probably the most prominent example of this currently - with Microsoft licensing the Mosaic Web browser to become Internet Explorer and Netscape hiring several of the Mosaic development team from the federally funded National Center for Supercomputer Applications (NCSA) at the University of Illinois. In the video world, the emerging wavelet technologies were largely developed with federal funding, including the development of working still image prototypes in software.
On March 23, 1998 the AVI Overview received the PC Webopaedia
Outstanding Page Award.
On February 4, 1999 was selected as a HotCool SuperSite.
jfm@rahul.net
| Back to category graphics - Discuss "AVI Graphics Format Overview" |
| Home - Search - About the project - Forum - Feedback |
© allanswers.org | Terms of use