wavelet toolbox: wdencmp function specific input gbl or lvd

In the wavelet toolbox, there is a function call wdencmp, which compress and denoise the wavelet, and there is one input that is very confusing, what does it mean by the choice of either 'gbl' or 'lvd'? what does gbl and lvd stand for? and how does the choice going to affect the output? Thanks

Answer 1

[Dhaniklal]

Hi,

I understand that you want to know about the function wdencmp and specifically input parameters gbl or lvd for image denoising.

Syntax:

[XC,CXC,LXC,PERF0,PERFL2] = wdencmp('gbl',X,wname,N,THR,SORH,KEEPAPP);

Please note that gbl is used for single global threshold and lvd is used for level dependent threshold. Also notice the input THR which stands for Threshold Level(s) to apply to wavelet coefficients.

The difference of using gbl or lvd primarily affects how THR is defined. Please go through the THR – Threshold section in the document given below and read the use cases of gbl and lvd mentioned.

Denoising or compression - MATLAB wdencmp - MathWorks India

Basically lvd could give more control over the Threshold levels in the three orientations: horizontal, diagonal, and vertical.

You might also want to check out a newer function wdenoise2() which was introduced in R2019a for similar use cases. Please follow the link below to know more about it.

Wavelet image denoising - MATLAB wdenoise2 - MathWorks India

Thanks,

Dhaniklal