How to use VPA (variable precision arithmetic) in calculating HH band via dwt on an image?

I have the following code:

img = imread('cameraman.tif');

[LL,LH,HL,HH] = dwt2(img, 'db1');

I have to calculate HH band using vpa (32 digits), instead of double precision.

Plz help in this regard.

Answer 1

[Stephan]

You can not do this. dwt2 accepts only double as input and outputs double. vpa works on symbolic variables and returns a symbolic variable:

>> vpa(pi)
 
ans =
 
3.1415926535897932384626433832795
 
>> whos ans
  Name      Size            Bytes  Class    Attributes

  ans       1x1                 8  sym                

So you will either get an error if you try to pass a symbolic variable to dwt2 or you will have to cast it to double, which also does not help you. What you can do is show 32 digits of the result calculated as double:

  >> a = pi/2

a =

    1.5708

>> sprintf('%.32g',a)

ans =

    '1.5707963267948965579989817342721'

>> whos
  Name      Size            Bytes  Class     Attributes

  a         1x1                 8  double              
  ans       1x33               66  char  

Maybe this helps.