freqz2

二维频率响应

语句

[H,f1,f2] = freqz2(h)

[H,f1,f2] = freqz2(h,[n1 n2])

[H,f1,f2] = freqz2(h,f1, f2)

[___] = freqz2(h,___,[dx dy])

freqz2(___)

说明

[H,f1,f2] = freqz2(h) 的返回值 H是h的64*64频率响应，f1和f2是长度为64的频率向量。 h 是一个二维的有限脉冲响应滤波器（FIR filter）,其形式为计算单元（computational molecule）。 

freqz2 所返回的 f1 和 f2 是在-1至1间标准化过的，1.0相当于采样频率的一半， 或π弧度。

[H,f1,f2] = freqz2(h,[n1 n2]) 返回的 H是 h的n2*n1 频率响应, f1和f2长度分别为n1和n2。[n1 n2]可以被指定为两个分离的参量n1,n2。

[H,f1,f2] = freqz2(h,f1, f2) 返回有限脉冲响应滤波器 h 在频率值在f1间f2的频率响应。f1 f2必须在-1.0到1.0范围内，1.0相当于采样频率的一半， 或π弧度。[f1 f2]可以被指定为两个分离的参量f1,f2。

[___] = freqz2(h,___,[dx dy]) 使用[dx dy]覆盖h中的样本间距。还可以指定一个标量来指定x和y维度中的间距。

freqz2(___) 在没有指定输出参数时，生成二维幅度频率响应的网格图。

示例

观察滤波器的频率响应

本示例展示了如何使用fwind1创建二维滤波器和如何使用freqz2观察该滤波器的频率响应

创建理想频率响应

Hd = zeros(16,16);
Hd(5:12,5:12) = 1;
Hd(7:10,7:10) = 0;

创建一维窗口。本示例使用长度为16的巴特兰窗口。

w = [0:2:16 16:-2:0]/16;

使用fwind1创建16*16滤波器和一维窗口。此滤波器最接近理想频率响应。

h = fwind1(Hd,w);

显示滤波器的实际频率响应。

colormap(parula(64))
freqz2(h,[32 32]);
axis ([-1 1 -1 1 0 1])

注：除h数据类型为single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64外，其他都是double

=====================原文========================

原文地址 https://ww2.mathworks.cn/help/images/ref/freqz2.html

freqz2

2-D frequency response

Syntax

[H,f1,f2] = freqz2(h)

[H,f1,f2] = freqz2(h,[n1 n2])

[H,f1,f2] = freqz2(h,f1, f2)

[___] = freqz2(h,___,[dx dy])

freqz2(___)

Description

[H,f1,f2] = freqz2(h) returns H, the 64-by-64 frequency response of h, and the frequency vectors f1 (of length 64) and f2 (of length 64). h is a two-dimensional FIR filter, in the form of a computational molecule.

freqz2 returns f1 and f2 as normalized frequencies in the range -1.0 to 1.0, where 1.0 corresponds to half the sampling frequency, or π radians.

[H,f1,f2] = freqz2(h,[n1 n2]) returns H, the n2-by-n1 frequency response of h, and the frequency vectors f1 (of length n1) and f2 (of length n2). You can also specify[n1 n2] as two separate arguments, n1,n2.

[H,f1,f2] = freqz2(h,f1, f2) returns the frequency response for the FIR filter h at frequency values in f1 and f2. These frequency values must be in the range -1.0 to 1.0, where 1.0 corresponds to half the sampling frequency, or π radians. You can also specify [f1 f2] as two separate arguments, f1, f2.

[___] = freqz2(h,___,[dx dy]) uses [dx dy] to override the intersample spacing in h. You can also specify a scalar to specify the same spacing in both the x and ydimensions.

freqz2(___) produces a mesh plot of the two-dimensional magnitude frequency response when no output arguments are specified.

Examples

View Frequency Response of Filter 

This example shows how to create a two-dimensional filter using fwind1 and how to view the filter's frequency response using freqz2.

Create an ideal frequency response.

Hd = zeros(16,16);
Hd(5:12,5:12) = 1;
Hd(7:10,7:10) = 0;

Create a 1-D window. This example uses a Bartlett window of length 16.

w = [0:2:16 16:-2:0]/16;

Create the 16-by-16 filter using fwind1 and the 1-D window. This filter gives the closest match to the ideal frequency response.

h = fwind1(Hd,w);

Display the actual frequency response of the filter.

colormap(parula(64))
freqz2(h,[32 32]);
axis ([-1 1 -1 1 0 1])