Understanding Hanning Window

[dan07]

I would like to understand how Hanning Window works. In the help section, the equation of Hanning Window is:

y_i = 0.5x_i[1 – cos ( ( 2 * PI * i  ) / n) ]

for i = 0, 1, 2, …, n – 1,

where n is the number of elements in X.

I created a array of four values: 150, 250, 250, 300. After Hanning Window I got the array: 0, 125, 250, 150

I am not able to realize how the equation was performed for each number because I don't understand where I will input the position of the value (first value of the series, second value of the series). The position its important because the same value 250 in the original array, resulted in different values in the array after Hanning, revealing that the position its important.

How would be the 4 equations to manipulate these four values in the original array?

Thanks for help

Dan07

[Yamaeda · Accepted solution]

y0 = 0,5*150*(1- cos(2*PI*0/4)) = 0

y1 = 0,5*250*(1-cos(2*PI*1/4)) = 125

y2 = 0,5*250*(1- cos(2*PI*2/4)) = 250

y3 = 0,5*300*(1- cos(2*PI*3/4)) = 150

Does that help?

/Y

[dan07]

Hello Yamaeda...

Thanks for the answer, your equation its correct. I did not know about the 0/4, 1/4, 2/4....

But I still have a problem, when I tested your equatio in Microsoft Excel, I got the correct results, but when I tried to perform the calculation using a pocket calculator (HP 10s), the result for COS its different from that obatined in excel. For example, COS (1), its 0.540302306 in excel, and 0.999847695 in HP 10s. Do you know what is happening?

Thanks

Daniel

Message Edited by dan07 on 11-26-2008 08:05 AM

[johnsold]

Daniel,

One is in degrees and  the other in radians. 

Lynn 

[dan07]

John...

you are right.

Problem solved!

Thanks all!

[NBS]

can u give me information about 1/4th hanning window used to calculate weighted average. 

[NBS]

Please can any one tell me about hanning window which is used for calculating weighted average.

[dan07]

Hello NBS

Sorry for the delayed answer. I don't know nothing about 1/4th hanning window used to calculate weighted average, but I will get some information about this and will send to you soon.

What kind of data you will apply the hanning window?

Thanks

Dan07

[NBS]

I am doing project on DCT based iris recognition.

I am going to apply it to a normalised iris image of size 88 X 512.

Before applying DCT 1/4th hanning window is applied twice one in horizontal direction and other in vertical.

got information about hanning but not abt 1/4th.

Really confused abt its use.

Hope that u will find some way for me.

thanks alot.

[dan07]

Hello NBS,

I searched by informations to help you with your problem, but I got no success doing this.

I got tons of information about hanning window, but not for 1/4th.

Sorry and good luck

Dan07