fft

Fourier analysis of tiff images using openCV

一曲冷凌霜 提交于 2020-05-30 08:12:36
问题 Image Loading To start I tried loading in .tif images using openCV but got the following error: Invalid bitsperpixel value read from TIFF header! Must be 1, 8, 16, 32 or 64. in function 'cv::TiffDecoder::readHeader' Checked using a hex editor to determine the bit depth of the image and it seems to be 16bit. After some trail and error I managed to find a solution using the code below. First loaded the image with the specialized tifffile library. Then saved it to a temporary file and finally

Discrete Fourier transform

你离开我真会死。 提交于 2020-05-24 10:11:43
问题 I am currently trying to write some fourier transform algorithm. I started with a simple DFT algorithm as described in the mathematical definition: public class DFT { public static Complex[] Transform(Complex[] input) { int N = input.Length; Complex[] output = new Complex[N]; double arg = -2.0 * Math.PI / (double)N; for (int n = 0; n < N; n++) { output[n] = new Complex(); for (int k = 0; k < N; k++) output[n] += input[k] * Complex.Polar(1, arg * (double)n * (double)k); } return output; } } So

How to multiply two 2D RFFT arrays (FFTPACK) to be compatible with NumPy's FFT?

被刻印的时光 ゝ 提交于 2020-05-20 05:05:50
问题 This bounty has ended . Answers to this question are eligible for a +250 reputation bounty. Bounty grace period ends in 23 hours . karlphillip is looking for a canonical answer : Detailed explanation and source code for a function that performs the correct multiplication of two 2D arrays transformed with FFTPACK RFFT. The validation procedure is already embedded in the code of the question: one simply needs to replace the line that says # this doesn't work with the function call that performs

Removal of horizontal stripes using openCV2

自作多情 提交于 2020-05-16 04:52:07
问题 I am new to openCV and I was wondering if there is a way to remove the periodic stripes in the lower half of this image. I looked at this post but couldn't quite understand what was going on: Removing periodic noise from an image using the Fourier Transform 回答1: Here is how to mitigate (reduce, but not totally eliminate) the lines using Fourier Transform and notch filtering processing with Python/OpenCV/Numpy. Since the horizontal lines in the input are very close, there will be horizontal

一幅图弄清DFT与DTFT,DFS的关系

南笙酒味 提交于 2020-04-24 22:43:55
很多同学学习了数字信号处理之后,被里面的几个名词搞的晕头转向,比如DFT,DTFT,DFS,FFT,FT,FS等,FT和FS属于信号与系统课程的内容,是对连续时间信号的处理,这里就不过多讨论,只解释一下前四者的关系。   首先说明一下,我不是数字信号处理专家,因此这里只站在学生的角度以最浅显易懂的性质来解释问题,而不涉及到任何公式运算。   学过卷积,我们都知道有 时域卷积定理 和 频域卷积定理 ,在这里只需要记住两点:1.在一个域的相乘等于另一个域的卷积;2.与脉冲函数的卷积,在每个脉冲的位置上将产生一个波形的镜像。(在任何一本信号与系统课本里,此两条性质有详细公式证明)   下面,就用这两条性质来说明DFT,DTFT,DFS,FFT之间的联系:   先看图片:   首先来说图(1)和图(2),对于一个模拟信号,如图(1)所示,要分析它的频率成分,必须变换到频域,这是通过傅立叶变换即 FT(Fourier Transform) 得到的,于是有了模拟信号的频谱,如图(2); 注意1:时域和频域都是连续的 !   但是,计算机只能处理数字信号,首先需要将原模拟信号在 时域离散化 ,即在时域对其进行采样,采样脉冲序列如图(3)所示,该采样序列的频谱如图(4),可见它的频谱也是一系列的脉冲。所谓时域采样,就是在时域对信号进行相乘,(1)×(3)后可以得到离散时间信号x[n],如图(5

How to perform the FFT to a wave-file using NAudio

爷,独闯天下 提交于 2020-04-15 13:03:28
问题 I'm working with the NAudio-library and would like to perform the fast fourier transformation to a WaveStream. I saw that NAudio has already built-in the FFT but how do I use it? I heard i have to use the SampleAggregator class. 回答1: You need to read this entire blog article to best understand the following code sample I lifted to ensure the sample is preserved even if the article isn't: using (WaveFileReader reader = new WaveFileReader(fileToProcess)) { IWaveProvider stream32 = new

「学习笔记」多项式

◇◆丶佛笑我妖孽 提交于 2020-04-08 05:01:57
「学习笔记」多项式 把一直学不懂的各种大常数 \(O(n\log n)\) 的神奇多项式算法总结一下…… 证明什么的比较简略…… 还有我今天才知道预处理一下单位根会快很多 \(qwq\) 1、 \(FFT\) 最没用的一个 首先我们能写出一个 \(O(n^2)\) 的暴力 这个你都不会就可以退役了(某位dalao题解中的) 要确定一个多项式,我们发现只要代 \(f(1),f(2),f(3),...,f(n+m)\) 然后暴力插值就可以了。 还是不行。但是 聪明的数学家们 发现单位根有分治的特性,然后 \(FFT\) 就发明出来了。 \(FFT\) 分两步,一步 \(DFT\) ,一步 \(IDFT\) 。 \(Complex:\) struct Complex{ double x,y; Complex(double u=0,double v=0){x=u,y=v;} }; Complex operator + (Complex a,Complex b){ return Complex(a.x+b.x,a.y+b.y); } Complex operator - (Complex a,Complex b){ return Complex(a.x-b.x,a.y-b.y); } Complex operator * (Complex a,Complex b){ return

bzoj3684 大朋友的多叉树

你离开我真会死。 提交于 2020-04-08 05:01:34
Description 我们的大朋友很喜欢计算机科学,而且尤其喜欢多叉树。对于一棵带有正整数点权的有根多叉树,如果它满足这样的性质,我们的大朋友就会将其称作神犇的:点权为1的结点是叶子结点;对于任一点权大于1的结点u,u的孩子数目deg[u]属于集合D,且u的点权等于这些孩子结点的点权之和。 给出一个整数s,你能求出根节点权值为s的神犇多叉树的个数吗?请参照样例以更好的理解什么样的两棵多叉树会被视为不同的。 我们只需要知道答案关于950009857(453*2^21+1,一个质数)取模后的值。 Input 第一行有2个整数s,m。 第二行有m个互异的整数,d[1],d[2],…,d[m],为集合D中的元素。 Output 输出一行仅一个整数,表示答案模950009857的值。 Sample Input 4 2 2 3 Sample Output 10 HINT 数据规模: 1<=m<s<=10^5, 2<=d[i]<=s,有3组小数据和3组大数据。 获得新知识: 拉格朗日反演 不知道怎么证 结论还是比较好记的 获得新模板:fft的基本操作 //%std #include<iostream> #include<cstdio> #include<cstdlib> #include<cstring> #include<string> #include<algorithm>

only integers, slices (`:`), ellipsis (`…`), numpy.newaxis (`None`) and integer or boolean arrays are valid indices

六月ゝ 毕业季﹏ 提交于 2020-04-05 08:07:44
问题 I am implementing fft as part of my homework. My problem lies in the implemention of shuffling data elements using bit reversal. I get the following warning: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future. data[x], data[y] = data[y], data[x] And the auto grading system (provided by university) returns the following: error: only integers, slices ( : ), ellipsis ( ... ), numpy.newaxis ( None ) and integer or boolean arrays are valid

only integers, slices (`:`), ellipsis (`…`), numpy.newaxis (`None`) and integer or boolean arrays are valid indices

让人想犯罪 __ 提交于 2020-04-05 08:07:29
问题 I am implementing fft as part of my homework. My problem lies in the implemention of shuffling data elements using bit reversal. I get the following warning: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future. data[x], data[y] = data[y], data[x] And the auto grading system (provided by university) returns the following: error: only integers, slices ( : ), ellipsis ( ... ), numpy.newaxis ( None ) and integer or boolean arrays are valid