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Zernike polynomials
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<h2 id="definitions">Definitions</h2> <p>There are <a href="/facts/Even_and_odd_functions/tGHWJqAa">even and odd</a> Zernike polynomials. The even Zernike polynomials are defined as </p> Z n m ( ρ , φ ) = R n m ( ρ ) cos ( m φ ) {\displaystyle Z_{n}^{m}(\rho ,\varphi )=R_{n}^{m}(\rho )\,\cos(m\,\varphi )\!} <p>(even function over the azimuthal angle φ {\displaystyle \varphi } ), and the odd Zernike polynomials are defined as </p> Z n − m ( ρ , φ ) = R n m ( ρ ) sin ( m φ ) , {\displaystyle Z_{n}^{-m}(\rho ,\varphi )=R_{n}^{m}(\rho )\,\sin(m\,\varphi ),\!} <p>(odd function over the azimuthal angle φ {\displaystyle \varphi } ) where <i>m</i> and <i>n</i> are nonnegative <a href="/facts/Integer/PUwwrawx">integers</a> with <i>n ≥ m ≥ 0</i> (<i>m</i> = 0 for spherical Zernike polynomials), <i> φ {\displaystyle \varphi } </i> is the <a href="/facts/Azimuth/kEyt9nJ3">azimuthal</a> <a href="/facts/Angle/gFUTEQYq">angle</a>, <i>ρ</i> is the radial distance 0 ≤ ρ ≤ 1 {\displaystyle 0\leq \rho \leq 1} , and R n m {\displaystyle R_{n}^{m}} are the radial polynomials defined below. Zernike polynomials have the property of being limited to a range of −1 to +1, i.e. | Z n m ( ρ , φ ) | ≤ 1 {\displaystyle |Z_{n}^{m}(\rho ,\varphi )|\leq 1} . The radial polynomials R n m {\displaystyle R_{n}^{m}} are defined as </p> R n m ( ρ ) = ∑ k = 0 n − m 2 ( − 1 ) k ( n − k ) ! k ! ( n + m 2 − k ) ! ( n − m 2 − k ) ! ρ n − 2 k {\displaystyle R_{n}^{m}(\rho )=\sum _{k=0}^{\tfrac {n-m}{2}}{\frac {(-1)^{k}\,(n-k)!}{k!\left({\tfrac {n+m}{2}}-k\right)!\left({\tfrac {n-m}{2}}-k\right)!}}\;\rho ^{n-2k}} <p>for even <i>n</i> − <i>m</i>, while it is 0 for odd <i>n</i> − <i>m</i>. A special value is </p> R n m ( 1 ) = 1. {\displaystyle R_{n}^{m}(1)=1.} <h3>Other representations</h3> <p>Rewriting the ratios of factorials in the radial part as products of <a href="/facts/Binomial_coefficient/Tsx7eY5h">binomials</a> shows that the coefficients are integer numbers: </p> R n m ( ρ ) = ∑ k = 0 n − m 2 ( − 1 ) k ( n − k k ) ( n − 2 k n − m 2 − k ) ρ n − 2 k {\displaystyle R_{n}^{m}(\rho )=\sum _{k=0}^{\tfrac {n-m}{2}}(-1)^{k}{\binom {n-k}{k}}{\binom {n-2k}{{\tfrac {n-m}{2}}-k}}\rho ^{n-2k}} . <p>A notation as terminating <a href="/facts/Hypergeometric_function/yTEC6NBJ">Gaussian hypergeometric functions</a> is useful to reveal recurrences, to demonstrate that they are special cases of <a href="/facts/Jacobi_polynomials/5oKJKB1W">Jacobi polynomials</a>, to write down the differential equations, etc.: </p> R n m ( ρ ) = ( − 1 ) ( n − m ) / 2 ρ m P ( n − m ) / 2 ( m , 0 ) ( 1 − 2 ρ 2 ) = ( n n + m 2 ) ρ n 2 F 1 ( − n + m 2 , − n − m 2 ; − n ; ρ − 2 ) = ( − 1 ) n − m 2 ( n + m 2 m ) ρ m 2 F 1 ( 1 + n + m 2 , − n − m 2 ; 1 + m ; ρ 2 ) {\displaystyle {\begin{aligned}R_{n}^{m}(\rho )&=(-1)^{(n-m)/2}\rho ^{m}P_{(n-m)/2}^{(m,0)}(1-2\rho ^{2})\\&={\binom {n}{\tfrac {n+m}{2}}}\rho ^{n}\ {}_{2}F_{1}\left(-{\tfrac {n+m}{2}},-{\tfrac {n-m}{2}};-n;\rho ^{-2}\right)\\&=(-1)^{\tfrac {n-m}{2}}{\binom {\tfrac {n+m}{2}}{m}}\rho ^{m}\ {}_{2}F_{1}\left(1+{\tfrac {n+m}{2}},-{\tfrac {n-m}{2}};1+m;\rho ^{2}\right)\end{aligned}}} <p>for <i>n</i> − <i>m</i> even. </p><p>The inverse relation expands ρ j {\displaystyle \rho ^{j}} for fixed m ≤ j {\displaystyle m\leq j} into R n m ( ρ ) {\displaystyle R_{n}^{m}(\rho )} </p> ρ j = ∑ n ≡ m ( mod 2 ) j h j , n , m R n m ( ρ ) {\displaystyle \rho ^{j}=\sum _{n\equiv m{\pmod {2}}}^{j}h_{j,n,m}R_{n}^{m}(\rho )} <p>with rational coefficients h j , n , m {\displaystyle h_{j,n,m}} <a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p> h j , n , m = n + 1 1 + j + n 2 ( ( j − m ) / 2 ( n − m ) / 2 ) ( ( j + n ) / 2 ( n − m ) / 2 ) {\displaystyle h_{j,n,m}={\frac {n+1}{1+{\frac {j+n}{2}}}}{\frac {\binom {(j-m)/2}{(n-m)/2}}{\binom {(j+n)/2}{(n-m)/2}}}} <p>for even j − m = 0 , 2 , 4 , … {\displaystyle j-m=0,2,4,\ldots } . </p><p>The factor ρ n − 2 k {\displaystyle \rho ^{n-2k}} in the radial polynomial R n m ( ρ ) {\displaystyle R_{n}^{m}(\rho )} may be expanded in a <a href="/facts/Bernstein_polynomial/XkJFDDIB">Bernstein basis</a> of b s , n / 2 ( ρ 2 ) {\displaystyle b_{s,n/2}(\rho ^{2})} for even n {\displaystyle n} or ρ {\displaystyle \rho } times a function of b s , ( n − 1 ) / 2 ( ρ 2 ) {\displaystyle b_{s,(n-1)/2}(\rho ^{2})} for odd n {\displaystyle n} in the range ⌊ n / 2 ⌋ − k ≤ s ≤ ⌊ n / 2 ⌋ {\displaystyle \lfloor n/2\rfloor -k\leq s\leq \lfloor n/2\rfloor } . The radial polynomial may therefore be expressed by a finite number of Bernstein Polynomials with rational coefficients: </p> R n m ( ρ ) = 1 ( ⌊ n / 2 ⌋ ⌊ m / 2 ⌋ ) ρ n mod 2 ∑ s = ⌊ m / 2 ⌋ ⌊ n / 2 ⌋ ( − 1 ) ⌊ n / 2 ⌋ − s ( s ⌊ m / 2 ⌋ ) ( ( n + m ) / 2 s + ⌈ m / 2 ⌉ ) b s , ⌊ n / 2 ⌋ ( ρ 2 ) . {\displaystyle R_{n}^{m}(\rho )={\frac {1}{\binom {\lfloor n/2\rfloor }{\lfloor m/2\rfloor }}}\rho ^{n\mod 2}\sum _{s=\lfloor m/2\rfloor }^{\lfloor n/2\rfloor }(-1)^{\lfloor n/2\rfloor -s}{\binom {s}{\lfloor m/2\rfloor }}{\binom {(n+m)/2}{s+\lceil m/2\rceil }}b_{s,\lfloor n/2\rfloor }(\rho ^{2}).} <h3>Noll's sequential indices</h3> <p>Applications often involve linear algebra, where an integral over a product of Zernike polynomials and some other factor builds a matrix elements. To enumerate the rows and columns of these matrices by a single index, a conventional mapping of the two indices <i>n</i> and <i>m</i> to a single index <i>j</i> has been introduced by Noll.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> The table of this association Z n m → Z j {\displaystyle Z_{n}^{m}\rightarrow Z_{j}} starts as follows (sequence A176988 in the <a href="/facts/On-Line_Encyclopedia_of_Integer_Sequences/yow6cVsU">OEIS</a>). j = n ( n + 1 ) 2 + | m | + { 0 , m > 0 ∧ n ≡ { 0 , 1 } ( mod 4 ) ; 0 , m < 0 ∧ n ≡ { 2 , 3 } ( mod 4 ) ; 1 , m ≥ 0 ∧ n ≡ { 2 , 3 } ( mod 4 ) ; 1 , m ≤ 0 ∧ n ≡ { 0 , 1 } ( mod 4 ) . {\displaystyle j={\frac {n(n+1)}{2}}+|m|+\left\{{\begin{array}{ll}0,&m>0\land n\equiv \{0,1\}{\pmod {4}};\\0,&m<0\land n\equiv \{2,3\}{\pmod {4}};\\1,&m\geq 0\land n\equiv \{2,3\}{\pmod {4}};\\1,&m\leq 0\land n\equiv \{0,1\}{\pmod {4}}.\end{array}}\right.} </p> <table><tbody><tr><th>n,m</th><td>0,0</td><td>1,1</td><td>1,−1</td><td>2,0</td><td>2,−2</td><td>2,2</td><td>3,−1</td><td>3,1</td><td>3,−3</td><td>3,3</td></tr><tr><th>j</th><td>1</td><td>2</td><td>3</td><td>4</td><td>5</td><td>6</td><td>7</td><td>8</td><td>9</td><td>10</td></tr><tr><th>n,m</th><td>4,0</td><td>4,2</td><td>4,−2</td><td>4,4</td><td>4,−4</td><td>5,1</td><td>5,−1</td><td>5,3</td><td>5,−3</td><td>5,5</td></tr><tr><th>j</th><td>11</td><td>12</td><td>13</td><td>14</td><td>15</td><td>16</td><td>17</td><td>18</td><td>19</td><td>20</td></tr></tbody></table> <p>The rule is the following. </p> <ul><li>The even Zernike polynomials <i>Z</i> with m > 0 {\displaystyle m>0} obtain even indices <i>j.</i></li> <li>The odd <i>Z</i> where m < 0 {\displaystyle m<0} obtain odd indices <i>j</i>.</li> <li>Within a given <i>n</i>, a lower | m | {\displaystyle \left\vert m\right\vert } results in a lower <i>j</i>.</li></ul> <h3>OSA/ANSI standard indices</h3> <p><a href="/facts/The_Optical_Society/9WkJwyhr">OSA</a> <a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> and <a href="/facts/American_National_Standards_Institute/p3d1TQCb">ANSI</a> single-index Zernike polynomials using: </p> j = n ( n + 2 ) + l 2 {\displaystyle j={\frac {n(n+2)+l}{2}}} <table><tbody><tr><th>n,l</th><td>0,0</td><td>1,−1</td><td>1,1</td><td>2,−2</td><td>2,0</td><td>2,2</td><td>3,−3</td><td>3,−1</td><td>3,1</td><td>3,3</td></tr><tr><th>j</th><td>0</td><td>1</td><td>2</td><td>3</td><td>4</td><td>5</td><td>6</td><td>7</td><td>8</td><td>9</td></tr><tr><th>n,l</th><td>4,−4</td><td>4,−2</td><td>4,0</td><td>4,2</td><td>4,4</td><td>5,−5</td><td>5,−3</td><td>5,−1</td><td>5,1</td><td>5,3</td></tr><tr><th>j</th><td>10</td><td>11</td><td>12</td><td>13</td><td>14</td><td>15</td><td>16</td><td>17</td><td>18</td><td>19</td></tr></tbody></table> <h3>Fringe/University of Arizona indices</h3> <p>The Fringe indexing scheme is used in commercial optical design software and optical testing in, e.g., <a href="/facts/Photolithography/FTHsauvy">photolithography</a>.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p><p> j = ( 1 + n + | l | 2 ) 2 − 2 | l | + ⌊ 1 − sgn l 2 ⌋ {\displaystyle j=\left(1+{\frac {n+|l|}{2}}\right)^{2}-2|l|+\left\lfloor {\frac {1-\operatorname {sgn} l}{2}}\right\rfloor } </p><p>where sgn l {\displaystyle \operatorname {sgn} l} is the <a href="/facts/Sign_function/VADy9zQq">sign or signum function</a>. The first 20 fringe numbers are listed below. </p> <table><tbody><tr><th>n,l</th><td>0,0</td><td>1,1</td><td>1,−1</td><td>2,0</td><td>2,2</td><td>2,−2</td><td>3,1</td><td>3,−1</td><td>4,0</td><td>3,3</td></tr><tr><th>j</th><td>1</td><td>2</td><td>3</td><td>4</td><td>5</td><td>6</td><td>7</td><td>8</td><td>9</td><td>10</td></tr><tr><th>n,l</th><td>3,−3</td><td>4,2</td><td>4,−2</td><td>5,1</td><td>5,−1</td><td>6,0</td><td>4,4</td><td>4,−4</td><td>5,3</td><td>5,−3</td></tr><tr><th>j</th><td>11</td><td>12</td><td>13</td><td>14</td><td>15</td><td>16</td><td>17</td><td>18</td><td>19</td><td>20</td></tr></tbody></table> <h3>Wyant indices</h3> <p><a href="/facts/James_C._Wyant/46zvAJL8">James C. Wyant</a> uses the "Fringe" indexing scheme except it starts at 0 instead of 1 (subtract 1).<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> This method is commonly used including interferogram analysis software in Zygo interferometers and the open source software DFTFringe. </p> <h3>Rodrigues Formula</h3> <p>They satisfy the <a href="/facts/Rodrigues%2527_formula/r0lMDQEV">Rodrigues' formula</a> </p> Z n m ( x ) = x − m ( n − m 2 ) ! ( d d ( x 2 ) ) n − m 2 [ x n + m ( x 2 − 1 ) n − m 2 ] {\displaystyle Z_{n}^{m}(x)={\frac {x^{-m}}{\left({\frac {n-m}{2}}\right)!}}\left({\frac {d}{d\left(x^{2}\right)}}\right)^{\frac {n-m}{2}}\left[x^{n+m}\left(x^{2}-1\right)^{\frac {n-m}{2}}\right]} <p>and can be related to the <a href="/facts/Jacobi_polynomials/5oKJKB1W">Jacobi polynomials</a> as </p> Z n m ( x ) = x m P n − m 2 ( 0 , m ) ( 2 x 2 − 1 ) P n − m 2 ( 0 , m ) ( 1 ) {\displaystyle Z_{n}^{m}(x)=x^{m}{\frac {P_{\frac {n-m}{2}}^{(0,m)}\left(2x^{2}-1\right)}{P_{\frac {n-m}{2}}^{(0,m)}(1)}}} . <h2 id="properties">Properties</h2> <h3>Orthogonality</h3> <p>The orthogonality in the radial part reads<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p> ∫ 0 1 2 n + 2 R n m ( ρ ) 2 n ′ + 2 R n ′ m ( ρ ) ρ d ρ = δ n , n ′ {\displaystyle \int _{0}^{1}{\sqrt {2n+2}}R_{n}^{m}(\rho )\,{\sqrt {2n'+2}}R_{n'}^{m}(\rho )\,\rho d\rho =\delta _{n,n'}} <p>or </p><p> ∫ 1 0 R n m ( ρ ) R n ′ m ( ρ ) ρ d ρ = δ n , n ′ 2 n + 2 . {\displaystyle {\underset {0}{\overset {1}{\mathop {\int } }}}\,R_{n}^{m}(\rho )R_{{n}'}^{m}(\rho )\rho d\rho ={\frac {{\delta }_{n,{n}'}}{2n+2}}.} </p><p>Orthogonality in the angular part is represented by the <a href="/facts/List_of_integrals_of_trigonometric_functions/lPygFUJk">elementary</a> </p> ∫ 0 2 π cos ( m φ ) cos ( m ′ φ ) d φ = ϵ m π δ m , m ′ , {\displaystyle \int _{0}^{2\pi }\cos(m\varphi )\cos(m'\varphi )\,d\varphi =\epsilon _{m}\pi \delta _{m,m'},} ∫ 0 2 π sin ( m φ ) sin ( m ′ φ ) d φ = π δ m , m ′ ; m ≠ 0 , {\displaystyle \int _{0}^{2\pi }\sin(m\varphi )\sin(m'\varphi )\,d\varphi =\pi \delta _{m,m'};\quad m\neq 0,} ∫ 0 2 π cos ( m φ ) sin ( m ′ φ ) d φ = 0 , {\displaystyle \int _{0}^{2\pi }\cos(m\varphi )\sin(m'\varphi )\,d\varphi =0,} <p>where ϵ m {\displaystyle \epsilon _{m}} (sometimes called the <a href="/facts/Carl_Neumann/1MfDa0mo">Neumann factor</a> because it frequently appears in conjunction with Bessel functions) is defined as <i>2</i> if m = 0 {\displaystyle m=0} and <i>1</i> if m ≠ 0 {\displaystyle m\neq 0} . The product of the angular and radial parts establishes the orthogonality of the Zernike functions with respect to both indices if integrated over the unit disk, </p> ∫ Z n l ( ρ , φ ) Z n ′ l ′ ( ρ , φ ) d 2 r = ϵ l π 2 n + 2 δ n , n ′ δ l , l ′ , {\displaystyle \int Z_{n}^{l}(\rho ,\varphi )Z_{n'}^{l'}(\rho ,\varphi )\,d^{2}r={\frac {\epsilon _{l}\pi }{2n+2}}\delta _{n,n'}\delta _{l,l'},} <p>where d 2 r = ρ d ρ d φ {\displaystyle d^{2}r=\rho \,d\rho \,d\varphi } is the <a href="/facts/Jacobian_matrix_and_determinant/0tNv6o8j">Jacobian</a> of the circular coordinate system, and where n − l {\displaystyle n-l} and n ′ − l ′ {\displaystyle n'-l'} are both even. </p> <h3>Zernike transform</h3> <p>Any sufficiently smooth real-valued phase field over the unit disk G ( ρ , φ ) {\displaystyle G(\rho ,\varphi )} can be represented in terms of its Zernike coefficients (odd and even), just as periodic functions find an orthogonal representation with the <a href="/facts/Fourier_series/s3fsxPAT">Fourier series</a>. We have </p> G ( ρ , φ ) = ∑ m , n [ a m , n Z n m ( ρ , φ ) + b m , n Z n − m ( ρ , φ ) ] , {\displaystyle G(\rho ,\varphi )=\sum _{m,n}\left[a_{m,n}Z_{n}^{m}(\rho ,\varphi )+b_{m,n}Z_{n}^{-m}(\rho ,\varphi )\right],} <p>where the coefficients can be calculated using <a href="/facts/Inner_product/HoyjElEy">inner products</a>. On the space of L 2 {\displaystyle L^{2}} functions on the unit disk, there is an inner product defined by </p> ⟨ F , G ⟩ := ∫ F ( ρ , φ ) G ( ρ , φ ) ρ d ρ d φ . {\displaystyle \langle F,G\rangle :=\int F(\rho ,\varphi )G(\rho ,\varphi )\rho d\rho d\varphi .} <p>The Zernike coefficients can then be expressed as follows: </p> a m , n = 2 n + 2 ϵ m π ⟨ G ( ρ , φ ) , Z n m ( ρ , φ ) ⟩ , b m , n = 2 n + 2 ϵ m π ⟨ G ( ρ , φ ) , Z n − m ( ρ , φ ) ⟩ . {\displaystyle {\begin{aligned}a_{m,n}&={\frac {2n+2}{\epsilon _{m}\pi }}\left\langle G(\rho ,\varphi ),Z_{n}^{m}(\rho ,\varphi )\right\rangle ,\\b_{m,n}&={\frac {2n+2}{\epsilon _{m}\pi }}\left\langle G(\rho ,\varphi ),Z_{n}^{-m}(\rho ,\varphi )\right\rangle .\end{aligned}}} <p>Alternatively, one can use the known values of phase function <i>G</i> on the circular grid to form a system of equations. The phase function is retrieved by the unknown-coefficient weighted product with (known values) of Zernike polynomial across the unit grid. Hence, coefficients can also be found by solving a linear system, for instance by matrix inversion. Fast algorithms to calculate the forward and inverse Zernike transform use symmetry properties of <a href="/facts/Trigonometric/K4hfaC6F">trigonometric</a> functions, separability of radial and azimuthal parts of Zernike polynomials, and their rotational symmetries. </p> <h3>Symmetries</h3> <p>The <a href="/facts/List_of_trigonometric_identities/Xw9Jx8Vz">reflections of trigonometric functions</a> result that the parity with respect to reflection along the <i>x</i> axis is </p> Z n l ( ρ , φ ) = Z n l ( ρ , − φ ) {\displaystyle Z_{n}^{l}(\rho ,\varphi )=Z_{n}^{l}(\rho ,-\varphi )} for <i>l</i> ≥ 0, Z n l ( ρ , φ ) = − Z n l ( ρ , − φ ) {\displaystyle Z_{n}^{l}(\rho ,\varphi )=-Z_{n}^{l}(\rho ,-\varphi )} for <i>l</i> < 0. <p>The <a href="/facts/List_of_trigonometric_identities/Xw9Jx8Vz"><i>π</i> shifts of trigonometric functions</a> result that the parity with respect to point reflection at the center of coordinates is </p> Z n l ( ρ , φ ) = ( − 1 ) l Z n l ( ρ , φ + π ) , {\displaystyle Z_{n}^{l}(\rho ,\varphi )=(-1)^{l}Z_{n}^{l}(\rho ,\varphi +\pi ),} <p>where ( − 1 ) l {\displaystyle (-1)^{l}} could as well be written ( − 1 ) n {\displaystyle (-1)^{n}} because n − l {\displaystyle n-l} as even numbers are only cases to get non-vanishing Zernike polynomials. (If <i>n</i> is even then <i>l</i> is also even. If <i>n</i> is odd, then <i>l</i> is also odd.) This property is sometimes used to categorize Zernike polynomials into even and odd polynomials in terms of their angular dependence. (it is also possible to add another category with <i>l</i> = 0 since it has a special property of no angular dependence.) </p> <ul><li>Angularly even Zernike polynomials: Zernike polynomials with even <i>l</i> so that Z n l ( ρ , φ ) = Z n l ( ρ , φ + π ) . {\displaystyle Z_{n}^{l}(\rho ,\varphi )=Z_{n}^{l}(\rho ,\varphi +\pi ).} </li> <li>Angularly odd Zernike polynomials: Zernike polynomials with odd <i>l</i> so that Z n l ( ρ , φ ) = − Z n l ( ρ , φ + π ) . {\displaystyle Z_{n}^{l}(\rho ,\varphi )=-Z_{n}^{l}(\rho ,\varphi +\pi ).} </li></ul> <p>The radial polynomials are also either even or odd, depending on order <i>n</i> or <i>m</i>: </p> R n m ( ρ ) = ( − 1 ) n R n m ( − ρ ) = ( − 1 ) m R n m ( − ρ ) . {\displaystyle R_{n}^{m}(\rho )=(-1)^{n}R_{n}^{m}(-\rho )=(-1)^{m}R_{n}^{m}(-\rho ).} <p>These equalities are easily seen since R n m ( ρ ) {\displaystyle R_{n}^{m}(\rho )} with an odd (even) <i>m</i> contains only odd (even) powers to <i>ρ</i> (see examples of R n m ( ρ ) {\displaystyle R_{n}^{m}(\rho )} below). </p><p>The <a href="/facts/List_of_trigonometric_identities/Xw9Jx8Vz">periodicity of the trigonometric functions</a> results in invariance if rotated by multiples of 2 π / l {\displaystyle 2\pi /l} radian around the center: </p> Z n l ( ρ , φ + 2 π k l ) = Z n l ( ρ , φ ) , k = 0 , ± 1 , ± 2 , ⋯ . {\displaystyle Z_{n}^{l}\left(\rho ,\varphi +{\tfrac {2\pi k}{l}}\right)=Z_{n}^{l}(\rho ,\varphi ),\qquad k=0,\pm 1,\pm 2,\cdots .} <h3>As eigenfunctions of a differential operator</h3> <p>The Zernike polynomials are eigenfunctions of the Zernike differential operator, in modern formulation<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> </p> L [ f ] = ∇ 2 f − ( r ⋅ ∇ ) 2 f − 2 r ⋅ ∇ f {\displaystyle {\begin{aligned}L\left[f\right]=\nabla ^{2}f-({\bf {r}}\cdot \nabla )^{2}f-2{\bf {r}}\cdot \nabla f\end{aligned}}} <p>self-adjoint over the unit disk, with negative eigenvalues L [ Z n m ] = − n ( n + 2 ) Z n m {\displaystyle L[Z_{n}^{m}]=-n(n+2)Z_{n}^{m}} . Other self-adjoint differential operators can be constructed for which the Zernike polynomials form a spectrum, for example ∇ ⋅ ( 1 − ρ 2 ) ∇ Z n m = ( m 2 − n ( n + 2 ) ) Z n m {\displaystyle \nabla \cdot (1-\rho ^{2})\nabla Z_{n}^{m}=\left(m^{2}-n(n+2)\right)Z_{n}^{m}} (relating to rough surface <a href="/facts/Bidirectional_reflectance_distribution_function/9LtejD2e">BRDFs</a><a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a>), which differs from the above by a factor ∂ φ φ {\displaystyle \partial _{\varphi \varphi }} . </p> <h3>Recurrence relations</h3> <p>The Zernike polynomials satisfy the following recurrence relation which depends neither on the degree nor on the azimuthal order of the radial polynomials:<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> </p> R n m ( ρ ) + R n − 2 m ( ρ ) = ρ [ R n − 1 | m − 1 | ( ρ ) + R n − 1 m + 1 ( ρ ) ] . {\displaystyle {\begin{aligned}R_{n}^{m}(\rho )+R_{n-2}^{m}(\rho )=\rho \left[R_{n-1}^{\left|m-1\right|}(\rho )+R_{n-1}^{m+1}(\rho )\right]{\text{ .}}\end{aligned}}} <p>From the definition of R n m {\displaystyle R_{n}^{m}} it can be seen that R m m ( ρ ) = ρ m {\displaystyle R_{m}^{m}(\rho )=\rho ^{m}} and R m + 2 m ( ρ ) = ( ( m + 2 ) ρ 2 − ( m + 1 ) ) ρ m {\displaystyle R_{m+2}^{m}(\rho )=((m+2)\rho ^{2}-(m+1))\rho ^{m}} . The following three-term recurrence relation<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> then allows to calculate all other R n m ( ρ ) {\displaystyle R_{n}^{m}(\rho )} : </p> R n m ( ρ ) = 2 ( n − 1 ) ( 2 n ( n − 2 ) ρ 2 − m 2 − n ( n − 2 ) ) R n − 2 m ( ρ ) − n ( n + m − 2 ) ( n − m − 2 ) R n − 4 m ( ρ ) ( n + m ) ( n − m ) ( n − 2 ) . {\displaystyle R_{n}^{m}(\rho )={\frac {2(n-1)(2n(n-2)\rho ^{2}-m^{2}-n(n-2))R_{n-2}^{m}(\rho )-n(n+m-2)(n-m-2)R_{n-4}^{m}(\rho )}{(n+m)(n-m)(n-2)}}{\text{ .}}} <p>The above relation is especially useful since the derivative of R n m {\displaystyle R_{n}^{m}} can be calculated from two radial Zernike polynomials of adjacent degree:<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p> d d ρ R n m ( ρ ) = ( 2 n m ( ρ 2 − 1 ) + ( n − m ) ( m + n ( 2 ρ 2 − 1 ) ) ) R n m ( ρ ) − ( n + m ) ( n − m ) R n − 2 m ( ρ ) 2 n ρ ( ρ 2 − 1 ) . {\displaystyle {\frac {\operatorname {d} }{\operatorname {d} \!\rho }}R_{n}^{m}(\rho )={\frac {(2nm(\rho ^{2}-1)+(n-m)(m+n(2\rho ^{2}-1)))R_{n}^{m}(\rho )-(n+m)(n-m)R_{n-2}^{m}(\rho )}{2n\rho (\rho ^{2}-1)}}{\text{ .}}} <p>The differential equation of the Gaussian Hypergeometric Function is equivalent to </p> ρ 2 ( ρ 2 − 1 ) d 2 d ρ 2 R n m ( ρ ) = [ n ( n + 2 ) ρ 2 − m 2 ] R n m ( ρ ) + ρ ( 1 − 3 ρ 2 ) d d ρ R n m ( ρ ) . {\displaystyle \rho ^{2}(\rho ^{2}-1){\frac {d^{2}}{d\rho ^{2}}}R_{n}^{m}(\rho )=[n(n+2)\rho ^{2}-m^{2}]R_{n}^{m}(\rho )+\rho (1-3\rho ^{2}){\frac {d}{d\rho }}R_{n}^{m}(\rho ).} <h2 id="examples">Examples</h2> <h3>Radial polynomials</h3> <p>The first few radial polynomials are: </p> R 0 0 ( ρ ) = 1 {\displaystyle R_{0}^{0}(\rho )=1\,} R 1 1 ( ρ ) = ρ {\displaystyle R_{1}^{1}(\rho )=\rho \,} R 2 0 ( ρ ) = 2 ρ 2 − 1 {\displaystyle R_{2}^{0}(\rho )=2\rho ^{2}-1\,} R 2 2 ( ρ ) = ρ 2 {\displaystyle R_{2}^{2}(\rho )=\rho ^{2}\,} R 3 1 ( ρ ) = 3 ρ 3 − 2 ρ {\displaystyle R_{3}^{1}(\rho )=3\rho ^{3}-2\rho \,} R 3 3 ( ρ ) = ρ 3 {\displaystyle R_{3}^{3}(\rho )=\rho ^{3}\,} R 4 0 ( ρ ) = 6 ρ 4 − 6 ρ 2 + 1 {\displaystyle R_{4}^{0}(\rho )=6\rho ^{4}-6\rho ^{2}+1\,} R 4 2 ( ρ ) = 4 ρ 4 − 3 ρ 2 {\displaystyle R_{4}^{2}(\rho )=4\rho ^{4}-3\rho ^{2}\,} R 4 4 ( ρ ) = ρ 4 {\displaystyle R_{4}^{4}(\rho )=\rho ^{4}\,} R 5 1 ( ρ ) = 10 ρ 5 − 12 ρ 3 + 3 ρ {\displaystyle R_{5}^{1}(\rho )=10\rho ^{5}-12\rho ^{3}+3\rho \,} R 5 3 ( ρ ) = 5 ρ 5 − 4 ρ 3 {\displaystyle R_{5}^{3}(\rho )=5\rho ^{5}-4\rho ^{3}\,} R 5 5 ( ρ ) = ρ 5 {\displaystyle R_{5}^{5}(\rho )=\rho ^{5}\,} R 6 0 ( ρ ) = 20 ρ 6 − 30 ρ 4 + 12 ρ 2 − 1 {\displaystyle R_{6}^{0}(\rho )=20\rho ^{6}-30\rho ^{4}+12\rho ^{2}-1\,} R 6 2 ( ρ ) = 15 ρ 6 − 20 ρ 4 + 6 ρ 2 {\displaystyle R_{6}^{2}(\rho )=15\rho ^{6}-20\rho ^{4}+6\rho ^{2}\,} R 6 4 ( ρ ) = 6 ρ 6 − 5 ρ 4 {\displaystyle R_{6}^{4}(\rho )=6\rho ^{6}-5\rho ^{4}\,} R 6 6 ( ρ ) = ρ 6 . {\displaystyle R_{6}^{6}(\rho )=\rho ^{6}.\,} <h3>Zernike polynomials</h3> <p>The first few Zernike modes, at various indices,<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> are shown below. They are normalized such that: ∫ 0 2 π ∫ 0 1 Z 2 ⋅ ρ d ρ d ϕ = π {\displaystyle \int _{0}^{2\pi }\int _{0}^{1}Z^{2}\cdot \rho \,d\rho \,d\phi =\pi } , which is equivalent to Var ( Z ) unit circle = 1 {\displaystyle \operatorname {Var} (Z)_{\text{unit circle}}=1} . </p> <table><tbody><tr><th> Z n l {\displaystyle Z_{n}^{l}} </th><th>OSA/ANSIindex( j {\displaystyle j} )</th><th>Nollindex ( j {\displaystyle j} )</th><th>Wyantindex ( j {\displaystyle j} )</th><th>Fringe/UAindex( j {\displaystyle j} )</th><th>Radialdegree( n {\displaystyle n} )</th><th>Azimuthaldegree( l {\displaystyle l} )</th><th> Z j {\displaystyle Z_{j}} </th><th>Classical name</th></tr><tr><td> Z 0 0 {\displaystyle Z_{0}^{0}} </td><td>00</td><td>01</td><td>00</td><td>01</td><td>0</td><td>00</td><td> 1 {\displaystyle 1} </td><td><a href="/facts/Piston_(optics)/uDmsRCSw">Piston</a> (see, <a href="/facts/Wigner_semicircle_distribution/d10fufTU">Wigner semicircle distribution</a>)</td></tr><tr><td> Z 1 − 1 {\displaystyle Z_{1}^{-1}} </td><td>01</td><td>03</td><td>02</td><td>03</td><td>1</td><td>−1</td><td> 2 ρ sin ϕ {\displaystyle 2\rho \sin \phi } </td><td><a href="/facts/Tilt_(optics)/Nt9xsSS8">Tilt</a> (Y-Tilt, vertical tilt)</td></tr><tr><td> Z 1 1 {\displaystyle Z_{1}^{1}} </td><td>02</td><td>02</td><td>01</td><td>02</td><td>1</td><td>+1</td><td> 2 ρ cos ϕ {\displaystyle 2\rho \cos \phi } </td><td><a href="/facts/Tilt_(optics)/Nt9xsSS8">Tilt</a> (X-Tilt, horizontal tilt)</td></tr><tr><td> Z 2 − 2 {\displaystyle Z_{2}^{-2}} </td><td>03</td><td>05</td><td>05</td><td>06</td><td>2</td><td>−2</td><td> 6 ρ 2 sin 2 ϕ {\displaystyle {\sqrt {6}}\rho ^{2}\sin 2\phi } </td><td><a href="/facts/Astigmatism_(optical_systems)/svYYGDPS">Oblique astigmatism</a></td></tr><tr><td> Z 2 0 {\displaystyle Z_{2}^{0}} </td><td>04</td><td>04</td><td>03</td><td>04</td><td>2</td><td>00</td><td> 3 ( 2 ρ 2 − 1 ) {\displaystyle {\sqrt {3}}(2\rho ^{2}-1)} </td><td><a href="/facts/Defocus_aberration/AuE5r5Wv">Defocus</a> (longitudinal position)</td></tr><tr><td> Z 2 2 {\displaystyle Z_{2}^{2}} </td><td>05</td><td>06</td><td>04</td><td>05</td><td>2</td><td>+2</td><td> 6 ρ 2 cos 2 ϕ {\displaystyle {\sqrt {6}}\rho ^{2}\cos 2\phi } </td><td>Vertical astigmatism</td></tr><tr><td> Z 3 − 3 {\displaystyle Z_{3}^{-3}} </td><td>06</td><td>09</td><td>10</td><td>11</td><td>3</td><td>−3</td><td> 8 ρ 3 sin 3 ϕ {\displaystyle {\sqrt {8}}\rho ^{3}\sin 3\phi } </td><td>Vertical trefoil</td></tr><tr><td> Z 3 − 1 {\displaystyle Z_{3}^{-1}} </td><td>07</td><td>07</td><td>07</td><td>08</td><td>3</td><td>−1</td><td> 8 ( 3 ρ 3 − 2 ρ ) sin ϕ {\displaystyle {\sqrt {8}}(3\rho ^{3}-2\rho )\sin \phi } </td><td><a href="/facts/Coma_(optics)/Ik0LSlET">Vertical coma</a></td></tr><tr><td> Z 3 1 {\displaystyle Z_{3}^{1}} </td><td>08</td><td>08</td><td>06</td><td>07</td><td>3</td><td>+1</td><td> 8 ( 3 ρ 3 − 2 ρ ) cos ϕ {\displaystyle {\sqrt {8}}(3\rho ^{3}-2\rho )\cos \phi } </td><td>Horizontal coma</td></tr><tr><td> Z 3 3 {\displaystyle Z_{3}^{3}} </td><td>09</td><td>10</td><td>09</td><td>10</td><td>3</td><td>+3</td><td> 8 ρ 3 cos 3 ϕ {\displaystyle {\sqrt {8}}\rho ^{3}\cos 3\phi } </td><td>Oblique trefoil</td></tr><tr><td> Z 4 − 4 {\displaystyle Z_{4}^{-4}} </td><td>10</td><td>15</td><td>17</td><td>18</td><td>4</td><td>−4</td><td> 10 ρ 4 sin 4 ϕ {\displaystyle {\sqrt {10}}\rho ^{4}\sin 4\phi } </td><td>Oblique quadrafoil</td></tr><tr><td> Z 4 − 2 {\displaystyle Z_{4}^{-2}} </td><td>11</td><td>13</td><td>12</td><td>13</td><td>4</td><td>−2</td><td> 10 ( 4 ρ 4 − 3 ρ 2 ) sin 2 ϕ {\displaystyle {\sqrt {10}}(4\rho ^{4}-3\rho ^{2})\sin 2\phi } </td><td>Oblique secondary astigmatism</td></tr><tr><td> Z 4 0 {\displaystyle Z_{4}^{0}} </td><td>12</td><td>11</td><td>08</td><td>09</td><td>4</td><td>00</td><td> 5 ( 6 ρ 4 − 6 ρ 2 + 1 ) {\displaystyle {\sqrt {5}}(6\rho ^{4}-6\rho ^{2}+1)} </td><td><a href="/facts/Spherical_aberration/x7V1JMQ9">Primary spherical</a></td></tr><tr><td> Z 4 2 {\displaystyle Z_{4}^{2}} </td><td>13</td><td>12</td><td>11</td><td>12</td><td>4</td><td>+2</td><td> 10 ( 4 ρ 4 − 3 ρ 2 ) cos 2 ϕ {\displaystyle {\sqrt {10}}(4\rho ^{4}-3\rho ^{2})\cos 2\phi } </td><td>Vertical secondary astigmatism</td></tr><tr><td> Z 4 4 {\displaystyle Z_{4}^{4}} </td><td>14</td><td>14</td><td>16</td><td>17</td><td>4</td><td>+4</td><td> 10 ρ 4 cos 4 ϕ {\displaystyle {\sqrt {10}}\rho ^{4}\cos 4\phi } </td><td>Vertical quadrafoil</td></tr></tbody></table> <h2 id="applications">Applications</h2> <p class="note">Further information: <a href="/facts/Optical_aberration/YIqd9cA8">Optical_aberration § Zernike_model_of_aberrations</a></p> <p>The functions are a basis defined over the circular support area, typically the pupil planes in classical optical imaging at visible and infrared wavelengths through systems of lenses and mirrors of finite diameter. Their advantages are the simple analytical properties inherited from the simplicity of the radial functions and the factorization in radial and azimuthal functions; this leads, for example, to closed-form expressions of the two-dimensional <a href="/facts/Fourier_transform/XXhKJtc8">Fourier transform</a> in terms of Bessel functions.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a><a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> Their disadvantage, in particular if high <i>n</i> are involved, is the unequal distribution of nodal lines over the unit disk, which introduces ringing effects near the perimeter ρ ≈ 1 {\displaystyle \rho \approx 1} , which often leads attempts to define other orthogonal functions over the circular disk.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a><a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a><a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> </p><p>In precision optical manufacturing, Zernike polynomials are used to characterize higher-order errors observed in interferometric analyses. In wavefront slope sensors like the <a href="/facts/Shack%25E2%2580%2593Hartmann_wavefront_sensor/4EylMSFN">Shack-Hartmann</a>, Zernike coefficients of the wavefront can be obtained by fitting measured slopes with Zernike polynomial derivatives averaged over the sampling subapertures.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> In <a href="/facts/Optometry/7QlrKXm2">optometry</a> and <a href="/facts/Ophthalmology/024hdTWF">ophthalmology</a>, Zernike polynomials are used to describe <a href="/facts/Optical_aberration/YIqd9cA8">wavefront aberrations</a> of the <a href="/facts/Cornea/oKA6clQT">cornea</a> or <a href="/facts/Lens_(vision)/yWz7AdHV">lens</a> from an ideal spherical shape, which result in <a href="/facts/Refraction_error/bcWcSg2N">refraction errors</a>. They are also commonly used in <a href="/facts/Adaptive_optics/D1vWeHK0">adaptive optics</a>, where they can be used to characterize <a href="/facts/Atmospheric_turbulence/NpgFUhG5">atmospheric distortion</a>. Obvious applications for this are IR or visual astronomy and <a href="/facts/Satellite_imagery/V8LQh7jI">satellite imagery</a>. </p><p>Another application of the Zernike polynomials is found in the Extended Nijboer–Zernike theory of <a href="/facts/Diffraction/Mk80xXHT">diffraction</a> and aberrations. </p><p>Zernike polynomials are widely used as basis functions of <a href="/facts/Image_moments/C257gpkz">image moments</a>. Since Zernike polynomials are <a href="/facts/Orthogonal/JVIjYPog">orthogonal</a> to each other, Zernike moments can represent properties of an image with no redundancy or overlap of information between the moments. Although Zernike moments are significantly dependent on the <a href="/facts/Scaling_(geometry)/pFm6fvpu">scaling</a> and the <a href="/facts/Translation_(geometry)/KlpWmnfX">translation</a> of the object in a <a href="/facts/Region_of_interest/C8k58oC5">region of interest</a> (ROI), their <a href="/facts/Magnitude_(mathematics)/KCn9PoF0">magnitudes</a> are independent of the rotation angle of the object.<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> Thus, they can be utilized to extract <a href="/facts/Feature_(computer_vision)/GdfWRp5U">features</a> from images that describe the shape characteristics of an object. For instance, Zernike moments are utilized as shape descriptors to classify benign and malignant <a href="/facts/Breast_cancer/6hME580v">breast masses</a><a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> or the surface of vibrating disks.<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a> Zernike Moments also have been used to quantify shape of osteosarcoma cancer cell lines in single cell level.<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a> Moreover, Zernike Moments have been used for early detection of Alzheimer's disease by extracting discriminative information from the MR images of Alzheimer's disease, Mild cognitive impairment, and Healthy groups.<a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a> </p> <h2 id="higher-dimensions">Higher dimensions</h2> <p>The concept translates to higher dimensions <i>D</i> if multinomials x 1 i x 2 j ⋯ x D k {\displaystyle x_{1}^{i}x_{2}^{j}\cdots x_{D}^{k}} in Cartesian coordinates are converted to <a href="/facts/Hyperspherical_coordinates/bFu2S7E2">hyperspherical coordinates</a>, ρ s , s ≤ D {\displaystyle \rho ^{s},s\leq D} , multiplied by a product of Jacobi polynomials of the angular variables. In D = 3 {\displaystyle D=3} dimensions, the angular variables are <a href="/facts/Spherical_harmonics/bn98Gv2L">spherical harmonics</a>, for example. Linear combinations of the powers ρ s {\displaystyle \rho ^{s}} define an orthogonal basis R n ( l ) ( ρ ) {\displaystyle R_{n}^{(l)}(\rho )} satisfying </p> ∫ 0 1 ρ D − 1 R n ( l ) ( ρ ) R n ′ ( l ) ( ρ ) d ρ = δ n , n ′ {\displaystyle \int _{0}^{1}\rho ^{D-1}R_{n}^{(l)}(\rho )R_{n'}^{(l)}(\rho )d\rho =\delta _{n,n'}} . <p>(Note that a factor 2 n + D {\displaystyle {\sqrt {2n+D}}} is absorbed in the definition of <i>R</i> here, whereas in D = 2 {\displaystyle D=2} the normalization is chosen slightly differently. This is largely a matter of taste, depending on whether one wishes to maintain an integer set of coefficients or prefers tighter formulas if the orthogonalization is involved.) The explicit representation is<a class="footnote-ref" id="fnref:27" href="#fn:27"><sup>27</sup></a> </p> R n ( l ) ( ρ ) = 2 n + D ∑ s = 0 n − l 2 ( − 1 ) s ( n − l 2 s ) ( n − s − 1 + D 2 n − l 2 ) ρ n − 2 s = ( − 1 ) n − l 2 2 n + D ∑ s = 0 n − l 2 ( − 1 ) s ( n − l 2 s ) ( s − 1 + n + l + D 2 n − l 2 ) ρ 2 s + l = ( − 1 ) n − l 2 2 n + D ( n + l + D 2 − 1 n − l 2 ) ρ l 2 F 1 ( − n − l 2 , n + l + D 2 ; l + D 2 ; ρ 2 ) {\displaystyle {\begin{aligned}R_{n}^{(l)}(\rho )&={\sqrt {2n+D}}\sum _{s=0}^{\tfrac {n-l}{2}}(-1)^{s}{{\tfrac {n-l}{2}} \choose s}{n-s-1+{\tfrac {D}{2}} \choose {\tfrac {n-l}{2}}}\rho ^{n-2s}\\&=(-1)^{\tfrac {n-l}{2}}{\sqrt {2n+D}}\sum _{s=0}^{\tfrac {n-l}{2}}(-1)^{s}{{\tfrac {n-l}{2}} \choose s}{s-1+{\tfrac {n+l+D}{2}} \choose {\tfrac {n-l}{2}}}\rho ^{2s+l}\\&=(-1)^{\tfrac {n-l}{2}}{\sqrt {2n+D}}{{\tfrac {n+l+D}{2}}-1 \choose {\tfrac {n-l}{2}}}\rho ^{l}\ {}_{2}F_{1}\left(-{\tfrac {n-l}{2}},{\tfrac {n+l+D}{2}};l+{\tfrac {D}{2}};\rho ^{2}\right)\end{aligned}}} <p>for even n − l ≥ 0 {\displaystyle n-l\geq 0} , else identical to zero, with special case R n ( n ) ( ρ ) = 2 n + D ρ n . {\displaystyle R_{n}^{(n)}(\rho )={\sqrt {2n+D}}\rho ^{n}.} </p><p>Its differential equation for the Gaussian Hypergeometric Function is equivalent to ρ 2 ( ρ 2 − 1 ) d 2 d ρ 2 R n ( l ) ( ρ ) = [ n ρ 2 ( n + D ) − l ( D − 2 + l ) ] R n ( l ) ( ρ ) + ρ [ D − 1 − ( D + 1 ) ρ 2 ] d d ρ R n ( l ) ( ρ ) . {\displaystyle \rho ^{2}(\rho ^{2}-1){\frac {d^{2}}{d\rho ^{2}}}R_{n}^{(l)}(\rho )=\left[n\rho ^{2}(n+D)-l(D-2+l)\right]R_{n}^{(l)}(\rho )+\rho \left[D-1-(D+1)\rho ^{2}\right]{\frac {d}{d\rho }}R_{n}^{(l)}(\rho ).} </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Jacobi_polynomials/5oKJKB1W">Jacobi polynomials</a></li> <li>Nijboer–Zernike theory</li> <li><a href="/facts/Pseudo-Zernike_polynomials/uYJam4Q6">Pseudo-Zernike polynomials</a></li></ul> <ul><li><a href="/facts/Eric_W._Weisstein/FbMuVDep">Weisstein, Eric W.</a> <a href="https://mathworld.wolfram.com/ZernikePolynomial.html">"Zernike Polynomial"</a>. <i><a href="/facts/MathWorld/yc1jodbq">MathWorld</a></i>.</li> <li>Andersen, Torben B. (2018). <a href="https://doi.org/10.1364%2FOE.26.018878">"Efficient and robust recurrence relations for the Zernike circle polynomials and their derivatives in Cartesian coordinates"</a>. <i>Opt. Express</i>. 26 (15): 18878–18896. <a href="/facts/Bibcode_(identifier)/9HtdQSGB">Bibcode</a>:<a href="https://ui.adsabs.harvard.edu/abs/2018OExpr..2618878A">2018OExpr..2618878A</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1364%2FOE.26.018878">10.1364/OE.26.018878</a>. <a href="/facts/PMID_(identifier)/JlHAvMHt">PMID</a> <a href="https://pubmed.ncbi.nlm.nih.gov/30114148">30114148</a>.</li> <li>Bhatia, A. B.; Wolf, E. (1952). "The Zernike circle polynomials occurring in diffraction theory". <i>Proc. Phys. Soc. B</i>. 65 (11): 909–910. <a href="/facts/Bibcode_(identifier)/9HtdQSGB">Bibcode</a>:<a href="https://ui.adsabs.harvard.edu/abs/1952PPSB...65..909B">1952PPSB...65..909B</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1088%2F0370-1301%2F65%2F11%2F112">10.1088/0370-1301/65/11/112</a>.</li> <li>Callahan, P. G.; De Graef, M. (2012). "Precipitate shape fitting and reconstruction by means of 3D Zernike functions". <i>Modelling and Simulation in Materials Science and Engineering</i>. 20 (1): 015003. <a href="/facts/Bibcode_(identifier)/9HtdQSGB">Bibcode</a>:<a href="https://ui.adsabs.harvard.edu/abs/2012MSMSE..20a5003C">2012MSMSE..20a5003C</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1088%2F0965-0393%2F20%2F1%2F015003">10.1088/0965-0393/20/1/015003</a>. <a href="/facts/S2CID_(identifier)/ldJsHa2Y">S2CID</a> <a href="https://api.semanticscholar.org/CorpusID:121700658">121700658</a>.</li> <li>Campbell, C. E. (2003). 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Vol. 291. pp. 129–135. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1007%2F978-981-4585-42-2_15">10.1007/978-981-4585-42-2_15</a>. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-981-4585-41-5.</li> <li>Farokhi, Sajad; Shamsuddin, Siti Mariyam; Flusser, Jan; Sheikh, U.U.; Khansari, Mohammad; Jafari-Khouzani, Kourosh (2014). "Near infrared face recognition by combining Zernike moments and undecimated discrete wavelet transform". <i>Digital Signal Processing</i>. 31 (1): 13–27. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1016%2Fj.dsp.2014.04.008">10.1016/j.dsp.2014.04.008</a>.</li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="http://www.nijboerzernike.nl">The Extended Nijboer-Zernike website</a></li> <li><a href="http://www.mathworks.com/matlabcentral/fileexchange/38900-zernike-moments">MATLAB code for fast calculation of Zernike moments</a></li> <li><a href="https://github.com/tvwerkhoven/libtim-py/blob/master/libtim/zern.py">Python/NumPy library for calculating Zernike polynomials</a></li> <li><a href="http://www.telescope-optics.net/zernike_aberrations.htm">Zernike aberrations</a> at <a href="http://www.telescope-optics.net">Telescope Optics</a></li> <li><a href="http://www.wolframalpha.com/input/?i=Plot%5BZernikeR%5B7%2C3%2Cr%5D%2C%7Br%2C0%2C1%7D%5D">Example: using WolframAlpha to plot Zernike Polynomials</a></li> <li><a href="https://github.com/nschloe/orthopy#disk-s2">orthopy, a Python package computing orthogonal polynomials (including Zernike polynomials)</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Zernike, F. 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