HDR Wavelets

High Dynamic Range Wavelets

HDRWT is a multiscale processing tool (HDRWaveletTransform) designed to control the dynamic range of images. While wavelet transformations are able to separate image structures as a function of their characteristic scales, HDRWT is a step forward that further separates and isolates individual wavelet layers and their contained structures. In this way, local contrast of structures defined in a given wavelet layer is not perturbed by larger structures defined in subsequent layers.

I will translate !

As long as you have not clipped any highlights ( I told you not to ) images that appear blown on your screen mostly actually have the data there its just your hardware cannot display it correctly, If you look at your linear image if it is not saturated on there the information can be recovered with HDR wavelets

HDR Wavelets only work on stretched images , so I usually use this tool straight after using the histogram transformation tool

Also obviously your image has to have a HDR for the tool to work on and these inc things like bright nebula ( i.e. M42 ) or the core of bright galaxy's , it will have no or little effect evenly low brightness images

Below is open control panel of HDR wavelet

A) Number of layers-- This sets the number of wavelet layers to which HDR will be applied to, generally higher numbers 5 or 6 will be used on large scale objects like M42 and smaller numbers 2 , 3 or 4 on smaller scale objects like galaxy's of course this depends on your image scale , a little trial and error will get you a long way.

B) Overdrive--New to version 1.6 and enhances the wavelet tool i.e. if you after more contrast try this

C) Scaling function: Select a wavelet scaling function. Peaked scaling functions such as linear interpolation work better to isolate small-scale structures. Smooth scaling functions such as cubic B-spline work better to isolate larger scales.

D) To luminance-- Apply HDRWT only to the luminance of color images. I tend to use this all the time when using RGB images

E) Luminance mask-- Use a luminance mask to protect dark background regions. Again tend to use all the time

F) De ringing--Check to enable deringing , these may or may not be required

The word deringing here is not used in the context of circular protection its used in HDR wavelets to refer to protection of given area's and that means if HDR wavelets is overdoing things ,usually this is over emphasizing area's of low signal these deringing maps will support these areas

G) Small Scale--As it says creates small scale deringing maps, I tend to use small numbers less than 0.1 of course each image is different and requires good old trial and error

H) Large scale-- creates large scale deringing map , commonly used numbers between 0.1 and 0.4 , but you know trial and error

I) Output maps-- Check this to output deringing map , will help you to set G and H

J) Midtones Balance-- Applys a MTF , never used anything other than default

K) Number of iterations--More iterations will perform a stronger compression of dynamic range , I use 1 or 2

How to use HDR Wavelets

The example below ( M 82 ) will show you how HDR wavelets will recover detail from the supposed blown core

Click on Image to enlarge

To use HDR wavelets on the above I did the following

1) I selected the following -- 4 layers (A)... 3x3 linear Interpolation for the scaling function ( C ) ...Checked the luminance mask ( E ) and left everything else default and then I applied it to the top right original image, with the out put image being top left.

Now if you look at the top left image you will see that some of the dark dust lanes have been over emphasized ( good but no cigar )

2) So next I enabled the deringing tool ( Large scale H ) set to 0.2 ( Sorry trial and error again ) and applied it to the original image top right , with the output bottom left ( Cigar )

3) There is more detail to be extracted at a smaller scale , so next I selected 2 layers ( A ) with the rest of the settings as before and applied it to bottom left , with the out put image bottom right ( cigar ! )

I am sure you have noticed the great improvement in m82 , but also the large star has been inverted ( dark center ) , to stop this you will need to use a star mask , beyond this user guide for HDR wavelets but will show you how to in a later guide

Another example of HDR wavelets is M42 below

Click on image to enlarge

Have a look at the setting used above but mainly it was that I used 6 layers , 2 iterations and some deringing support

As powerful as HDR wavelets is there is no magic setting every image is different.