Digital image

From Includipedia, the inclusionist encyclopedia

A digital image is a representation of a two-dimensional image as a finite set of digital values, called picture elements or pixels. The digital image contains a fixed number of rows and columns of pixels. Pixels are the smallest individual element in an image, holding quantized values that represent the brightness of a given colour at any specific point.

Typically, the pixels are stored in computer memory as a raster image or raster map, a two-dimensional array of small integers. These values are often transmitted or stored in a compressed form.

Digital images can be created by a variety of input devices and techniques, such as digital cameras, scanners, coordinate-measuring machines, seismographic profiling, airborne radar, and more. They can also be synthetized from arbitrary non-image data, such as mathematical functions or three-dimensional geometric models; the latter being a major sub-area of computer graphics. The field of digital image processing is the study of algorithms for their transformation.

1 Image types
2 Image formats (preservation quality)
3 Image viewing
4 Image calibration
5 Notes and references
6 See also

Image types

Each pixel of an image is typically associated to a specific 'position' in some 2D region, and has a value consisting of one or more quantities (samples) related to that position. Digital images can be classified according to the number and nature of those samples:

The term digital image is also applied to data associated to points scattered over a three-dimensional region, such as produced by tomographic equipment. In that case, each datum is called a voxel.

Image formats (preservation quality)

A RAW file format is an image captured in its pure state by a chosen digital recording device. The Universal Photographic Imaging Guidelines (UPDIG) suggests this format be used when possible since RAW files produce the best quality images. This file format allows the photographer and the processing agent the greatest level of control and accuracy for output. Unfortunately, there is an issue of proprietary information [trade secrets] for some camera makers, but organizations are attempting to influence the manufacturers of them to avail these records publicly. An alternative may be a Digital Negative (DNG™) an Adobe® product described as “the public, archival format for digital camera raw data”. ^[1] Although this format is not yet universally accepted, support for the product is growing and archival confidence is building. ^[2]

According to A Ware Systems on-line, a website linked through the Adobe® TIFF developer resources page, a TIFF (TIF) is a Tagged Image File Format. ^[3] It has a flexible tagset, which enables metadata, data about the data, to be customized. This allows for a wide range of color space, bitdepth/datatype, and compression schemes. A TIFF permits the file size to be reduced with no loss in image quality. This format is recommended for output in print, multi-page file sharing, and preservation image files. Since all web browsers do not support TIFF, it should not be used for Web purposes. Also, the size limitation may be a concern. Currently, the file format cannot exceed four gigabytes. However, the size is expected to increase with subsequent versions of the design. As a result, no published standards or guidelines exist for determining the level of image quality required to create digital images. It is understood, "the larger the file is the more detail will be captured resulting in better reproductions." ^[4] Typically, images for the Web can be saved at 72 ppi (pixels per inch) while images for print should be saved at a minimum of 300 ppi. ^[5] However, a movement towards 600 ppi is becoming more commonly accepted.

Image viewing

The user can utilize different program to see the image. The GIF, JPEG and PNG images can be seen simply using a web browser because they are the standard internet image formats. The SVG format is more and more used in the web and is a standard W3C format.

Some viewers offer a slideshow utility, to see the images in a certain folder one after the other automatically. The user can utilize different program to see the image. The GIF, JPEG and PNG images can be seen simply using a web browser because they are the standard internet image formats. The SVG format is more and more used in the web and is a standard W3C format.

Some viewers offer a slideshow utility, to see the images in a certain folder one after the other automatically.

Image calibration

Proper use of a digital image usually requires knowledge of the relationship between it and the underlying phenomenon, which implies geometric and photometric (or sensor) calibration. One must also keep in mind the unavoidable errors that arise from the finite spatial resolution of the pixel array and the need to quantize each sample to a finite set of possible values.

Notes and references

^ Digital Negative (DNG) Specification. San Jose: Adobe, 2005. Vers. 1.1.0.0. p. 9. Accessed on October 10, 2007.
^ Anderson, Richard. The Universal Photographic Digital Imaging Guidelines. Ed. Michael Stewart. 2006. Vers. 2.0. UPDIG: Universal Photographic Digital Imaging Guidelines. p. 8. Accessed on October 12, 2007
^ TIFF, Tag Image File Format, FAQ Netherlands: n.d. A Ware Systems on-line. Accessed on October 14, 2007
^ The Canadian Heritage Information Network (CHIN) Capture Your Collections: A Guide for Managers Planning and Implementing Digitization Projects, Standards and Guidelines to Consider. Quebec: CHIN. Accessed December 9, 2007.
^ Anderson, Richard. The Universal Photographic Digital Imaging Guidelines. Ed. Michael Stewart. 2006. Vers. 2.0. UPDIG: Universal Photographic Digital Imaging Guidelines. p. 12. Accessed on October 12, 2007

Digital image

From Includipedia, the inclusionist encyclopedia

Contents

Image types

Image formats (preservation quality)

Image viewing

Image calibration

Notes and references

See also

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