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<title>Contrast (vision)</title>

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Contrast (vision)

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.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}

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</style><div role="note" class="hatnote navigation-not-searchable">For other uses, see <a href="Contrast_(disambiguation)" class="mw-redirect mw-disambig" title="Contrast (disambiguation)">Contrast</a>.</div>Contrast is the difference in <a href="Luminance" title="Luminance">luminance</a> or <a href="Color" title="Color">color</a> that makes an object (or its representation in an <a href="Image" title="Image">image</a> or <a href="Display_device" title="Display device">display</a>) visible against a background of different luminance or color.<a href="#cite_note-1">[1]</a> The human <a href="Visual_perception" title="Visual perception">visual system</a> is more sensitive to contrast than to absolute luminance; thus, we can perceive the world similarly despite significant changes in illumination throughout the day or across different locations.<a href="#cite_note-2">[2]</a>

The maximum contrast of an image is termed the <a href="Contrast_ratio" title="Contrast ratio">contrast ratio</a> or <a href="Dynamic_range" title="Dynamic range">dynamic range</a>. In images where the contrast ratio approaches the maximum possible for the medium, there is a conservation of contrast. In such cases, increasing contrast in certain parts of the image will necessarily result in a decrease in contrast elsewhere. Brightening an image increases contrast in darker areas but decreases it in brighter areas; conversely, darkening the image will have the opposite effect. <a href="Bleach_bypass" title="Bleach bypass">Bleach bypass</a> reduces contrast in the darkest and brightest parts of an image while enhancing luminance contrast in areas of intermediate <a href="Brightness" title="Brightness">brightness</a>.

<div class="mw-heading mw-heading2"><h2 id="Biological_contrast_sensitivity">Biological contrast sensitivity</h2></div>

Campbell and Robson (1968) showed that the human <a href="#Contrast_sensitivity">contrast sensitivity function</a> shows a typical <a href="Band-pass_filter" title="Band-pass filter">band-pass filter</a> shape peaking at around 4 cycles per degree (cpd or cyc/deg), with sensitivity dropping off either side of the peak.<a href="#cite_note-Campbell@1968-3">[3]</a> This can be observed by changing one's viewing distance from a "sweep <a href="Grating#Optical_grating" title="Grating">grating</a>" (shown below) showing many bars of a <a href="Sine_wave" title="Sine wave">sinusoidal</a> grating that go from high to low contrast along the bars, and go from narrow (high spatial frequency) to wide (low spatial frequency) bars across the width of the grating.

The high-frequency cut-off represents the <a href="Optics" title="Optics">optical</a> limitations of the visual system's ability to <a href="Optical_resolution" title="Optical resolution">resolve</a> detail and is typically about 60 cpd. The high-frequency cut-off is also related to the packing density of the <a href="Retina" title="Retina">retinal</a> <a href="Photoreceptor_cell" title="Photoreceptor cell">photoreceptor cells</a>: a finer matrix can resolve finer gratings.

The low frequency drop-off is due to <a href="Lateral_inhibition" title="Lateral inhibition">lateral inhibition</a> within the <a href="Retinal_ganglion_cell" title="Retinal ganglion cell">retinal ganglion cells</a>.<a href="#cite_note-4">[4]</a> A typical retinal ganglion cell's <a href="Receptive_field" title="Receptive field">receptive field</a> comprises a central region in which light either excites or inhibits the cell, and a surround region in which light has the opposite effects.

One experimental phenomenon is the inhibition of blue in the periphery if blue light is displayed against a white background, leading to a yellow surrounding. The yellow is derived from the inhibition of blue on the surroundings by the center. Since white minus blue is red and green, this mixes to become yellow.<a href="#cite_note-5">[5]</a>

For example, <a href="Display_contrast" title="Display contrast">in the case of graphical computer displays</a>, contrast depends on the properties of the picture source or file and the properties of the computer display, including its variable settings. For some screens <a href="Viewing_cone" title="Viewing cone">the angle</a> between the screen surface and the observer's line of sight is also important.

<div class="mw-heading mw-heading2"><h2 id="Quantifications">Quantifications</h2></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Display_contrast" title="Display contrast">Display contrast</a></div>

There are many possible definitions of contrast. Some include color; others do not. Russian scientist N. P. Travnikova laments, "Such a multiplicity of notions of contrast is extremely inconvenient. It complicates the solution of many applied problems and makes it difficult to compare the results published by different authors."<a href="#cite_note-Peli1990-6">[6]</a><a href="#cite_note-7">[7]</a>

Various definitions of contrast are used in different situations. Here, <a href="Luminance" title="Luminance">luminance</a> contrast is used as an example, but the formulas can also be applied to other physical quantities. In many cases, the definitions of contrast represent a ratio of the type

<mfrac>

<mtext>Luminance difference</mtext>

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<mtext>Average luminance</mtext>

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</mfrac>

</mrow>

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<annotation encoding="application/x-tex">{\displaystyle {\frac {\mbox{Luminance difference}}{\mbox{Average luminance}}}.}</annotation>

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</math><img src="./b4aad56885b55bc752770b1065c59a8fa5a0db04.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.505ex; width:22.901ex; height:6.009ex;" alt="{\displaystyle {\frac {\mbox{Luminance difference}}{\mbox{Average luminance}}}.}" loading="lazy"></dd></dl>

The rationale behind this is that a small difference is negligible if the average luminance is high, while the same small difference matters if the average luminance is low (see <a href="Weber%E2%80%93Fechner_law" title="Weber–Fechner law">Weber–Fechner law</a>). Below, some common definitions are given.

<div class="mw-heading mw-heading3"><h3 id="Weber_contrast">Weber contrast</h3></div>

Weber contrast is defined as<a href="#cite_note-Peli1990-6">[6]</a>

<mfrac>

<mrow>

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</mrow>

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<annotation encoding="application/x-tex">{\displaystyle {\frac {I-I_{\mathrm {b} }}{I_{\mathrm {b} }}},}</annotation>

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</math><img src="./d1d2a408ff570ccbc0e538e696e9fd34ebf86808.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.338ex; width:7.664ex; height:5.676ex;" alt="{\displaystyle {\frac {I-I_{\mathrm {b} }}{I_{\mathrm {b} }}},}" loading="lazy"></dd></dl>

with <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle I}">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle I}</annotation>

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</math><img src="./535ea7fc4134a31cbe2251d9d3511374bc41be9f.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.172ex; height:2.176ex;" alt="{\displaystyle I}" loading="lazy"> and <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle I_{\mathrm {b} }}">

<msub>

</mrow>

</msub>

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle I_{\mathrm {b} }}</annotation>

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</math><img src="./3a4e79a9c1cf7c7d7229115d3c91d7b77110f17d.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:2.169ex; height:2.509ex;" alt="{\displaystyle I_{\mathrm {b} }}" loading="lazy"> representing the luminance of the features and the background, respectively. The measure is also referred to as Weber fraction, since it is the term that is constant in <a href="Weber's_Law" class="mw-redirect" title="Weber's Law">Weber's Law</a>. Weber contrast is commonly used in cases where small features are present on a large uniform background, i.e., where the average luminance is approximately equal to the background luminance.<style data-mw-deduplicate="TemplateStyles:r1273380762/mw-parser-output/.tmulti">

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.mw-parser-output .tmulti .multiimageinner{display:flex;flex-direction:column}.mw-parser-output .tmulti .trow{display:flex;flex-direction:row;clear:left;flex-wrap:wrap;width:100%;box-sizing:border-box}.mw-parser-output .tmulti .tsingle{margin:1px;float:left}.mw-parser-output .tmulti .theader{clear:both;font-weight:bold;text-align:center;align-self:center;background-color:transparent;width:100%}.mw-parser-output .tmulti .thumbcaption{background-color:transparent}.mw-parser-output .tmulti .text-align-left{text-align:left}.mw-parser-output .tmulti .text-align-right{text-align:right}.mw-parser-output .tmulti .text-align-center{text-align:center}@media all and (max-width:720px){.mw-parser-output .tmulti .thumbinner{width:100%!important;box-sizing:border-box;max-width:none!important;align-items:center}.mw-parser-output .tmulti .trow{justify-content:center}.mw-parser-output .tmulti .tsingle{float:none!important;max-width:100%!important;box-sizing:border-box;text-align:center}.mw-parser-output .tmulti .tsingle .thumbcaption{text-align:left}.mw-parser-output .tmulti .trow>.thumbcaption{text-align:center}}@media screen{html.skin-theme-clientpref-night .mw-parser-output .tmulti .multiimageinner span:not(.skin-invert-image):not(.skin-invert):not(.bg-transparent) img{background-color:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .tmulti .multiimageinner span:not(.skin-invert-image):not(.skin-invert):not(.bg-transparent) img{background-color:white}}

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</style><div class="thumb tmulti tright"><div class="thumbinner multiimageinner" style="width:244px;max-width:244px"><div class="trow"><div class="tsingle" style="width:242px;max-width:242px"><div class="thumbimage"></div></div></div><div class="trow"><div class="tsingle" style="width:242px;max-width:242px"><div class="thumbimage"></div><div class="thumbcaption">A photograph of a leaf with several colors—the bottom image has an 11% saturation boost and around 10% increase in contrast.</div></div></div></div></div>

<div class="mw-heading mw-heading3"><h3 id="Michelson_contrast">Michelson contrast</h3></div>

Michelson contrast<a href="#cite_note-8">[8]</a> (also known as the visibility) is commonly used for patterns where both bright and dark features are equivalent and take up similar fractions of the area (e.g. <a href="Spatial_frequency" title="Spatial frequency">sine-wave gratings</a>). The Michelson contrast is defined as<a href="#cite_note-Peli1990-6">[6]</a>

<mfrac>

<mrow>

<msub>

</mrow>

</msub>

<msub>

</mrow>

</msub>

</mrow>

<mrow>

<msub>

</mrow>

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<annotation encoding="application/x-tex">{\displaystyle {\frac {I_{\mathrm {max} }-I_{\mathrm {min} }}{I_{\mathrm {max} }+I_{\mathrm {min} }}},}</annotation>

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</math><img src="./2f75b0dabafc3852c0b9c33efe7bd5235ed0aef2.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.338ex; width:12.633ex; height:5.676ex;" alt="{\displaystyle {\frac {I_{\mathrm {max} }-I_{\mathrm {min} }}{I_{\mathrm {max} }+I_{\mathrm {min} }}},}" loading="lazy"></dd></dl>

with <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle I_{\mathrm {max} }}">

<msub>

</mrow>

</msub>

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle I_{\mathrm {max} }}</annotation>

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</math><img src="./b2e3ae131f4cb6a62441f4beedeef61c6b76f932.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:4.314ex; height:2.509ex;" alt="{\displaystyle I_{\mathrm {max} }}" loading="lazy"> and <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle I_{\mathrm {min} }}">

<msub>

</mrow>

</msub>

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle I_{\mathrm {min} }}</annotation>

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</math><img src="./c47d42e240ac362f0d0f90f6a5dd87d4392c7a67.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:3.996ex; height:2.509ex;" alt="{\displaystyle I_{\mathrm {min} }}" loading="lazy"> representing the highest and lowest luminance. The denominator represents twice the average of the maximum and minimum luminances.<a href="#cite_note-9">[9]</a>

This form of contrast is an effective way to quantify contrast for periodic functions <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle f(x)}">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle f(x)}</annotation>

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</math><img src="./202945cce41ecebb6f643f31d119c514bec7a074.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:4.418ex; height:2.843ex;" alt="{\displaystyle f(x)}" loading="lazy"> and is also known as the modulation <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle m_{f}}">

<msub>

</mrow>

</msub>

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle m_{f}}</annotation>

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</math><img src="./a6b1ed1cca247d7fbe5a237f3c266a4e13850185.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:3.177ex; height:2.343ex;" alt="{\displaystyle m_{f}}" loading="lazy"> of a periodic signal <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle f}">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle f}</annotation>

</semantics>

</math><img src="./132e57acb643253e7810ee9702d9581f159a1c61.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:1.279ex; height:2.509ex;" alt="{\displaystyle f}" loading="lazy">. Modulation quantifies the relative amount by which the amplitude (or difference) <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle (f_{\text{max}}-f_{\text{min}})/2}">

<msub>

</mrow>

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<msub>

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</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle (f_{\text{max}}-f_{\text{min}})/2}</annotation>

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</math><img src="./b347dd7b25a28be6fa3ab57a47e4b2df0b241023.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:15.517ex; height:2.843ex;" alt="{\displaystyle (f_{\text{max}}-f_{\text{min}})/2}" loading="lazy"> of <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle f}">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle f}</annotation>

</semantics>

</math><img src="./132e57acb643253e7810ee9702d9581f159a1c61.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:1.279ex; height:2.509ex;" alt="{\displaystyle f}" loading="lazy"> stands out from the average value (or background) <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle (f_{\text{max}}+f_{\text{min}})/2}">

<msub>

</mrow>

</msub>

<msub>

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</mrow>

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle (f_{\text{max}}+f_{\text{min}})/2}</annotation>

</semantics>

</math><img src="./d134a7477c36219ee3ad8bdb72724ae1b3cae0f8.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:15.517ex; height:2.843ex;" alt="{\displaystyle (f_{\text{max}}+f_{\text{min}})/2}" loading="lazy">.

In general, <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle m_{f}}">

<msub>

</mrow>

</msub>

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle m_{f}}</annotation>

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</math><img src="./a6b1ed1cca247d7fbe5a237f3c266a4e13850185.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:3.177ex; height:2.343ex;" alt="{\displaystyle m_{f}}" loading="lazy"> refers to the contrast of the periodic signal <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle f}">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle f}</annotation>

</semantics>

</math><img src="./132e57acb643253e7810ee9702d9581f159a1c61.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:1.279ex; height:2.509ex;" alt="{\displaystyle f}" loading="lazy"> relative to its average value. If <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle m_{f}=0}">

<msub>

</mrow>

</msub>

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle m_{f}=0}</annotation>

</semantics>

</math><img src="./a88ece180fcfdf014d5a4423777584f58b8dcc6f.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:7.438ex; height:2.843ex;" alt="{\displaystyle m_{f}=0}" loading="lazy">, then <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle f}">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle f}</annotation>

</semantics>

</math><img src="./132e57acb643253e7810ee9702d9581f159a1c61.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:1.279ex; height:2.509ex;" alt="{\displaystyle f}" loading="lazy"> has no contrast. If two periodic functions <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle f}">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle f}</annotation>

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</math><img src="./132e57acb643253e7810ee9702d9581f159a1c61.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:1.279ex; height:2.509ex;" alt="{\displaystyle f}" loading="lazy"> and <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle g}">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle g}</annotation>

</semantics>

</math><img src="./d3556280e66fe2c0d0140df20935a6f057381d77.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:1.116ex; height:2.009ex;" alt="{\displaystyle g}" loading="lazy"> have the same average value, then <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle f}">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle f}</annotation>

</semantics>

</math><img src="./132e57acb643253e7810ee9702d9581f159a1c61.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:1.279ex; height:2.509ex;" alt="{\displaystyle f}" loading="lazy"> has more contrast than <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle g}">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle g}</annotation>

</semantics>

</math><img src="./d3556280e66fe2c0d0140df20935a6f057381d77.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:1.116ex; height:2.009ex;" alt="{\displaystyle g}" loading="lazy"> if <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle m_{f}>m_{g}}">

<msub>

</mrow>

</msub>

<msub>

</mrow>

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</mrow>

<annotation encoding="application/x-tex">{\displaystyle m_{f}>m_{g}}</annotation>

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</math><img src="./7fc29320e25442e4de59abbbed0793e286759170.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:9.337ex; height:2.509ex;" alt="{\displaystyle m_{f}>m_{g}}" loading="lazy">.<a href="#cite_note-10">[10]</a>

<div class="mw-heading mw-heading3"><h3 id="RMS_contrast">RMS contrast</h3></div>

<a href="Root_mean_square" title="Root mean square">Root mean square</a> (RMS) contrast does not depend on the spatial frequency content or the spatial distribution of contrast in the image. RMS contrast is defined as the standard deviation of the <a href="Pixel" title="Pixel">pixel</a> intensities:<a href="#cite_note-Peli1990-6">[6]</a>

<msqrt>

<mfrac>

<mrow>

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</mrow>

</munderover>

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<msup>

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</mrow>

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</mrow>

<annotation encoding="application/x-tex">{\displaystyle {\sqrt {{\frac {1}{MN}}\sum _{i=0}^{N-1}\sum _{j=0}^{M-1}\left(I_{ij}-{\bar {I}}\right)^{2}}}}</annotation>

</semantics>

</math><img src="./620c41377e48a6e3f680f14bc49f532446e5d67f.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -3.338ex; width:26.39ex; height:8.343ex;" alt="{\displaystyle {\sqrt {{\frac {1}{MN}}\sum _{i=0}^{N-1}\sum _{j=0}^{M-1}\left(I_{ij}-{\bar {I}}\right)^{2}}}}" loading="lazy"></dd></dl>

where intensities <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle I_{ij}}">

<msub>

</mrow>

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</mstyle>

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<annotation encoding="application/x-tex">{\displaystyle I_{ij}}</annotation>

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</math><img src="./b8e861c28675994decc6373478cade6f99e4f4df.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:2.5ex; height:2.843ex;" alt="{\displaystyle I_{ij}}" loading="lazy"> are the <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle i}">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle i}</annotation>

</semantics>

</math><img src="./add78d8608ad86e54951b8c8bd6c8d8416533d20.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:0.802ex; height:2.176ex;" alt="{\displaystyle i}" loading="lazy">-th <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle j}">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle j}</annotation>

</semantics>

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</math><img src="./f82cade9898ced02fdd08712e5f0c0151758a0dd.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:2.442ex; height:2.176ex;" alt="{\displaystyle M}" loading="lazy"> by <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle N}">

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<div class="mw-heading mw-heading3"><h3 id="Haziness_contrast">Haziness contrast</h3></div>

Alternative contrast measurement metrics, such as the haziness metric,<a href="#cite_note-11">[11]</a> have been developed to quantify contrast (or lack of contrast) with more intuitive notions of contrast: ability to differenciate different regions of the image.

<div class="mw-heading mw-heading2"><h2 id="Contrast_sensitivity">Contrast sensitivity</h2></div>

Contrast sensitivity is a measure of the ability to discern different <a href="Luminance" title="Luminance">luminances</a> in a static <a href="Image" title="Image">image</a>. It varies with age, increasing to a maximum around 20 years at <a href="Spatial_frequency" title="Spatial frequency">spatial frequencies</a> of about 2–5 cpd; aging then progressively attenuates contrast sensitivity beyond this peak. Factors such as cataracts and <a href="Diabetic_retinopathy" title="Diabetic retinopathy">diabetic retinopathy</a> also reduce contrast sensitivity.<a href="#cite_note-12">[12]</a> In the sweep grating figure below, at an ordinary viewing distance, the bars in the middle appear to be the longest due to their optimal spatial frequency. However, at a far viewing distance, the longest visible bars shift to what were originally the wide bars, now matching the spatial frequency of the middle bars at reading distance.

<div class="mw-heading mw-heading3"><h3 id="Contrast_sensitivity_and_visual_acuity">Contrast sensitivity and visual acuity</h3></div>

<a href="Visual_acuity" title="Visual acuity">Visual acuity</a> is a parameter that is frequently used to assess overall vision. However, diminished contrast sensitivity may cause decreased visual function in spite of normal visual acuity.<a href="#cite_note-13">[13]</a> For example, some individuals with <a href="Glaucoma" title="Glaucoma">glaucoma</a> may achieve 20/20 vision on acuity exams, yet struggle with <a href="Activities_of_daily_living" title="Activities of daily living">activities of daily living</a>, such as driving at night.

As mentioned above, contrast sensitivity describes the ability of the visual system to distinguish bright and dim components of a static image. Visual acuity can be defined as the angle with which one can resolve two points as being separate since the image is shown with 100% contrast and is projected onto the fovea of the retina.<a href="#cite_note-14">[14]</a> Thus, when an <a href="Optometrist" class="mw-redirect" title="Optometrist">optometrist</a> or <a href="Ophthalmologist" class="mw-redirect" title="Ophthalmologist">ophthalmologist</a> assesses a patient's visual acuity using a <a href="Snellen_chart" title="Snellen chart">Snellen chart</a> or some other <a href="Landolt_C" title="Landolt C">acuity chart</a>, the target image is displayed at high contrast, e.g., black letters of decreasing size on a white background. A subsequent contrast sensitivity exam may demonstrate difficulty with decreased contrast (using, e.g., the Pelli–Robson chart, which consists of uniform-sized but increasingly pale grey letters on a white background).

To assess a patient's contrast sensitivity, one of several diagnostic exams may be used. Most charts in an ophthalmologist's or optometrist's office will show images of varying contrast and <a href="Spatial_frequency" title="Spatial frequency">spatial frequency</a>. Parallel bars of varying width and contrast, known as sine-wave gratings, are sequentially viewed by the patient. The width of the bars and their distance apart represent spatial frequency, measured in cycles per degree.Studies have demonstrated that contrast sensitivity is maximum for spatial frequencies of 2-5 cpd, falling off for lower spatial frequencies and rapidly falling off for higher spatial frequencies. The upper limit for the human vision system is about 60 cpd. The correct identification of small letters requires the letter size be about 18-30 cpd.<a href="#cite_note-15">[15]</a> Contrast threshold can be defined as the minimum contrast that can be resolved by the patient. Contrast sensitivity is typically expressed as the <a href="Multiplicative_inverse" title="Multiplicative inverse">reciprocal</a> of the threshold contrast for detection of a given pattern (i.e., 1 ÷ contrast threshold).<a href="#cite_note-16">[16]</a>

Using the results of a contrast sensitivity exam, a contrast sensitivity curve can be plotted, with spatial frequency on the horizontal, and contrast threshold on the vertical axis. Also known as contrast sensitivity function (CSF), the plot demonstrates the normal range of contrast sensitivity, and will indicate diminished contrast sensitivity in patients who fall below the normal curve. Some graphs contain "contrast sensitivity acuity equivalents", with lower acuity values falling in the area under the curve. In patients with normal visual acuity and concomitant reduced contrast sensitivity, the area under the curve serves as a graphical representation of the visual deficit. It can be because of this impairment in contrast sensitivity that patients have difficulty driving at night, climbing stairs and other activities of daily living in which contrast is reduced.<a href="#cite_note-17">[17]</a>

Recent studies have demonstrated that intermediate-frequency sinusoidal patterns are optimally-detected by the retina due to the center-surround arrangement of neuronal receptive fields.<a href="#cite_note-18">[18]</a> In an intermediate spatial frequency, the peak (brighter bars) of the pattern is detected by the center of the receptive field, while the troughs (darker bars) are detected by the inhibitory periphery of the receptive field. For this reason, low- and high-spatial frequencies elicit excitatory and inhibitory impulses by overlapping frequency peaks and troughs in the center and periphery of the neuronal <a href="Receptive_field" title="Receptive field">receptive field</a>.<a href="#cite_note-19">[19]</a> Other environmental,<a href="#cite_note-20">[20]</a> physiological, and anatomical factors influence the neuronal transmission of sinusoidal patterns, including <a href="Adaptation" title="Adaptation">adaptation</a>.<a href="#cite_note-21">[21]</a>

Decreased contrast sensitivity arises from multiple etiologies, including retinal disorders such as <a href="Age-related_macular_degeneration" class="mw-redirect" title="Age-related macular degeneration">age-related macular degeneration</a> (ARMD), <a href="Amblyopia" title="Amblyopia">amblyopia</a>, lens abnormalities, such as <a href="Cataract" title="Cataract">cataract</a>, and by higher-order neural dysfunction, including <a href="Stroke" title="Stroke">stroke</a> and <a href="Alzheimer's_disease" title="Alzheimer's disease">Alzheimer's disease</a>.<a href="#cite_note-22">[22]</a> In light of the multitude of etiologies leading to decreased contrast sensitivity, contrast sensitivity tests are useful in the characterization and monitoring of dysfunction, and less helpful in detection of disease.

<div class="mw-heading mw-heading2"><h2 id="Contrast_threshold">Contrast threshold</h2></div>

A large-scale study of luminance contrast thresholds was done in the 1940s by Blackwell,<a href="#cite_note-blackwell-23">[23]</a> using a forced-choice procedure. Discs of various sizes and luminances were presented in different positions against backgrounds at a wide range of adaptation luminances, and subjects had to indicate where they thought the disc was being shown. After statistical pooling of results (90,000 observations by seven observers), the threshold for a given target size and luminance was defined as the Weber contrast level at which there was a 50% detection level. The experiment employed a discrete set of contrast levels, resulting in discrete values of threshold contrast. Smooth curves were drawn through these, and values tabulated. The resulting data have been used extensively in areas such as lighting engineering and road safety.<a href="#cite_note-25">[25]</a>

A separate study by Knoll et al<a href="#cite_note-26">[26]</a> investigated thresholds for point sources by requiring subjects to vary the brightness of the source to find the level at which it was just visible. A mathematical formula for the resulting threshold curve was proposed by <a href="Selig_Hecht" title="Selig Hecht">Hecht</a>,<a href="#cite_note-27">[27]</a> with separate branches for scotopic and photopic vision. Hecht's formula was used by Weaver<a href="#cite_note-28">[28]</a> to model the naked-eye visibility of stars. The same formula was used later by <a href="Bradley_Schaefer" title="Bradley Schaefer">Schaefer</a><a href="#cite_note-29">[29]</a> to model stellar visibility through a telescope.

<a href="Andrew_Crumey" title="Andrew Crumey">Crumey</a><a href="#cite_note-crumey-24">[24]</a> showed that Hecht's formula fitted the data very poorly at low light levels, so was not really suitable for modelling stellar visibility. Crumey instead constructed a more accurate and general model applicable to both the Blackwell and Knoll et al data. Crumey's model covers all light levels, from zero background luminance to daylight levels, and instead of parameter-tuning is based on an underlying linearity related to <a href="Ricco's_law" title="Ricco's law">Ricco's law</a>. Crumey used it to model astronomical visibility for targets of arbitrary size, and to study the effects of light pollution.

<div class="mw-heading mw-heading2"><h2 id="Test_images">Test images</h2></div>

Test images types<a href="#cite_note-30">[30]</a>

<ul><li>Pelli-Robson Contrast Sensitivity Chart</li>

<li>Regan chart</li>

<li>Arden grating chart</li>

<li>Campbell-Robson Contrast Sensitivity Chart<a href="#cite_note-31">[31]</a></li></ul>

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<ul><li><a href="Acutance" title="Acutance">Acutance</a> – Perception of image sharpness which is unrelated to actual resolution</li>

<li><a href="Color_blindness" title="Color blindness">Color blindness</a> – Decreased ability to see color or color differences</li>

<li><a href="Contrast_ratio" title="Contrast ratio">Contrast ratio</a> – Property of a display system</li>

<li><a href="Display_contrast" title="Display contrast">Display contrast</a> – Difference in appearance of two or more parts of a field seen simultaneously or successively</li>

<li><a href="Eye_examination" title="Eye examination">Eye examination</a> – Series of tests assessing vision and pertaining to the eyes</li>

<li><a href="Optical_resolution" title="Optical resolution">Optical resolution</a> – Ability of an imaging system to resolve detail</li>

<li><a href="Psychophysics" title="Psychophysics">Psychophysics</a> – Branch of knowledge relating physical stimuli and psychological perception</li>

<li><a href="Radiocontrast" class="mw-redirect" title="Radiocontrast">Radiocontrast</a> – Substance which enhances visibility in X-ray-based imagingPages displaying short descriptions of redirect targets</li>

<li><a href="Spatial_frequency" title="Spatial frequency">Spatial frequency</a> – Characteristic of any structure that is periodic across a position in space</li>

<li><a href="Visual_acuity" title="Visual acuity">Visual acuity</a> – Clarity of vision</li></ul>

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<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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<li id="cite_note-31"><a href="#cite_ref-31">^</a> <cite id="CITEREFTardifWatsonGiaschiGosselin2021" class="citation journal cs1">Tardif, Jessica; Watson, Marcus R.; Giaschi, Deborah; Gosselin, Frédéric (2021-03-09). <a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7985182">"The Curve Visible on the Campbell-Robson Chart Is Not the Contrast Sensitivity Function"</a>. Frontiers in Neuroscience. 15. Frontiers Media SA. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.3389%2Ffnins.2021.626466">10.3389/fnins.2021.626466</a>. <a href="ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/1662-453X">1662-453X</a>. <a href="PMC_(identifier)" class="mw-redirect" title="PMC (identifier)">PMC</a> <a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7985182">7985182</a>. <a href="PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/33767608">33767608</a>.</cite>

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<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="https://colorusage.arc.nasa.gov/luminance_cont.php">Details on luminance contrast</a></li></ul>

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