Image resolution

Source: Wikipedia, the free encyclopedia.

Image resolution is the level of detail of an image. The term applies to digital images, film images, and other types of images. "Higher resolution" means more image detail. Image resolution can be measured in various ways. Resolution quantifies how close lines can be to each other and still be visibly resolved. Resolution units can be tied to physical sizes (e.g. lines per mm, lines per inch), to the overall size of a picture (lines per picture height, also known simply as lines, TV lines, or TVL), or to angular subtense. Instead of single lines, line pairs are often used, composed of a dark line and an adjacent light line; for example, a resolution of 10 lines per millimeter means 5 dark lines alternating with 5 light lines, or 5 line pairs per millimeter (5 LP/mm). Photographic lens are most often quoted in line pairs per millimeter.

Types

The resolution of digital cameras can be described in many different ways.

Pixel count

The term resolution is often considered equivalent to

CIPA DCG-001 calls for notation such as "Number of Recorded Pixels 1000 × 1500".[1][2] According to the same standards, the "Number of Effective Pixels" that an image sensor or digital camera has is the count of pixel
sensors that contribute to the final image (including pixels not in said image but nevertheless support the image filtering process), as opposed to the number of total pixels, which includes unused or light-shielded pixels around the edges.

An image of N pixels height by M pixels wide can have any resolution less than N lines per picture height, or N TV lines. But when the pixel counts are referred to as "resolution", the convention is to describe the pixel resolution with the set of two positive

upper bounds
on image resolution.

Below is an illustration of how the same image might appear at different pixel resolutions, if the pixels were poorly rendered as sharp squares (normally, a smooth image reconstruction from pixels would be preferred, but for illustration of pixels, the sharp squares make the point better).

An image that is 2048 pixels in width and 1536 pixels in height has a total of 2048×1536 = 3,145,728 pixels or 3.1 megapixels. One could refer to it as 2048 by 1536 or a 3.1-megapixel image. The image would be a very low quality image (72ppi) if printed at about 28.5 inches wide, but a very good quality (300ppi) image if printed at about 7 inches wide.

The number of photodiodes in a color

demosaiced
to produce all three colors for each output pixel.

Spatial resolution

The terms blurriness and sharpness are used for digital images but other descriptors are used to reference the hardware capturing and displaying the images.

Spatial resolution in radiology is the ability of the imaging modality to differentiate two objects. Low spatial resolution techniques will be unable to differentiate between two objects that are relatively close together.

The 1951 USAF resolution test target is a classic test target used to determine spatial resolution of imaging sensors and imaging systems.
Image at left has a higher pixel count than the one to the right, but is still of worse spatial resolution.

The measure of how closely lines can be resolved in an image is called spatial resolution, and it depends on properties of the system creating the image, not just the pixel resolution in

pixels per inch
(ppi). For practical purposes the clarity of the image is decided by its spatial resolution, not the number of pixels in an image. In effect, spatial resolution is the number of independent pixel values per unit length.

The spatial resolution of consumer displays ranges from 50 to 800 pixel lines per inch. With scanners, optical resolution is sometimes used to distinguish spatial resolution from the number of pixels per inch.

In

diffraction, as well as by aberrations, imperfect focus, and atmospheric distortion. The ground sample distance
(GSD) of an image, the pixel spacing on the Earth's surface, is typically considerably smaller than the resolvable spot size.

In

electron microscopy
, line or fringe resolution is the minimum separation detectable between adjacent parallel lines (e.g. between planes of atoms), whereas point resolution is instead the minimum separation between adjacent points that can be both detected and interpreted e.g. as adjacent columns of atoms, for instance. The former often helps one detect periodicity in specimens, whereas the latter (although more difficult to achieve) is key to visualizing how individual atoms interact.

In Stereoscopic 3D images, spatial resolution could be defined as the spatial information recorded or captured by two viewpoints of a stereo camera (left and right camera).

Spectral resolution

Pixel encoding limits the information stored in a digital image, and the term color profile is used for digital images but other descriptors are used to reference the hardware capturing and displaying the images.

Spectral resolution is the ability to resolve spectral features and bands into their separate components.

Multispectral images can resolve even finer differences of spectrum or wavelength
by measuring and storing more than the traditional 3 of common RGB color images.

Temporal resolution

Temporal resolution (TR) is the precision of a measurement with respect to time.

frames per second
(frames/s), whereas high-speed cameras may resolve 50 to 300 frames/s, or even more.

The Heisenberg uncertainty principle describes the fundamental limit on the maximum spatial resolution of information about a particle's coordinates imposed by the measurement or existence of information regarding its momentum to any degree of precision.

This fundamental limitation can, in turn, be a factor in the maximum imaging resolution at subatomic scales, as can be encountered using scanning electron microscopes.

Radiometric resolution

reflectivity
can be represented, at least in theory. In practice, the effective radiometric resolution is typically limited by the noise level, rather than by the number of bits of representation.

Resolution in various media

This is a list of traditional, analogue horizontal resolutions for various media. The list only includes popular formats, not rare formats, and all values are approximate, because the actual quality can vary machine-to-machine or tape-to-tape. For ease-of-comparison, all values are for the NTSC system. (For PAL systems, replace 480 with 576.) Analog formats usually had less chroma resolution.

  • Analogue and early digital[3]

Many cameras and displays offset the color components relative to each other or mix up temporal with spatial resolution:

PPI Pixels mm
800 1000 31.8
300 1000 84.7
200 1000 127
72 1000 352.8
PPI Pixels mm
800 3150 100
300 1181 100
200 787 100
72 283 100
PPI Pixels mm Paper size
300 9921×14008 840×1186 A0
300 7016×9921 594×840 A1
300 4961×7016 420×594 A2
300 3508×4961 297×420 A3
300 2480×3508 210×297 A4
300 1748×2480 148×210 A5
300 1240×1748 105×148 A6
300 874×1240 74×105 A7
300 614×874 52×74 A8

See also

References

  1. ^ [1] Archived 2017-02-02 at the Wayback Machine Guideline for Noting Digital Camera Specifications in Catalogs. "The term 'Resolution' shall not be used for the number of recorded pixels"
  2. ^ ANSI/I3A IT10.7000–2004 Photography – Digital Still Cameras – Guidelines for Reporting Pixel-Related Specifications
  3. ^ "Video resolution comparison chart".
  4. ^ "Kodak VISION3 500T Color Negative Film 5219 / 7219 / SO-219" (PDF). July 2015.
  5. ^ [2] An analysis of film resolution
  6. ^ Understanding image sharpness part 1A: Resolution and MTF curves in film and lenses, by Norman Koren
  7. ^ "/Film Interview: IMAX Executives Talk 'The Hunger Games: Catching Fire' and IMAX Misconceptions". Slash Film. December 2, 2013. Retrieved December 17, 2013.
  8. ^ "Phaseone". Archived from the original on 2012-03-18.
  9. ^ "Leaf Aptus Medium Format Digital Backs". www.mamiyaleaf.com. Archived from the original on 2015-09-24. Retrieved 2013-11-06.
  10. ^ DxO. "Phase One IQ180 Digital Back: Tests and Reviews – DxOMark". www.dxomark.com.
  11. ^ Forret, Peter. "Megapixel calculator – toolstudio". web.forret.com.