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Glint in WorldView 2 Image

Hello All,

I got my hands on an 8 band WorldView 2 image, sadly the entire image is covered with sun glint since its a marine image... i would like to know of how to remove this glint problem... Thanks

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Have a read of this paper: Hedley et al. (2005) Simple and robust removal of sun glint for mapping shallow-water
benthos. International Journal of Remote Sensing Vol. 26, No. 10, 2107�??2112.

Step by step instructions to implement this method are available for ENVI (not ArcGIS sorry).

I use some IDL code from ENVI to do this instead of the above manual method, though I do generate the samples with the ROI tool by hand):

nirs=samples[*,*,7]
nird=data[*,*,7]
d=size(nirs,/dim)
i=where(nirs gt 0)
o=where(nird eq 0)
m=min(nirs)
m=nirs
m = m[(sort(m))[5 * N_ELEMENTS(m) / 100] ] 
out=0
help, m

foreach b, bindgen(6) do begin

    band=samples[*,*,b]
    r=linfit(nirs,band)
    band=data[*,*,b]
    deglint=long(band - r[1] * (nird - m)+0.5) 

    deglint=0
    if size(out, /n_dimensions) eq 0 then                 $  ;Image stack doesn't exist yet
      out=temporary(deglint)                                 $
    else                                                  $  ;Concatenate image to stack
      out=[[[temporary(out)]],[[temporary(deglint)]]]

endforeach

out=[[[temporary(out)]],[[data[*,*,6]]]]
out=[[[temporary(out)]],[[data[*,*,7]]]]

end

Again note that these methods are for ENVI, not ArcGIS. You could probably reimplement the code in numpy though.

Thanks lpinner, Now i got more to go on than before... as for the cook book i saw it before, and read it, sadly didnt understand much with what to do... considering that I'm still a beginner with all of this... I'll them out and see what i can come up with... BTW, as for the script that you attached, In Envi, where would i input it?

It requires a full ENVI+IDL install, not just the ENVI runtime. It also requires you have enough memory to load the entire image into RAM as I didn't bother writing any sort of tiling code, it was just a very rough hack that I whipped up to meet an immediate need.

To use my code:

Save the code to a file with a ".pro" extension
Start "ENVI + IDL" (not ENVI)
Load your WV2 image into ENVI.
In the main ENVI toolbar click File-> Export to IDL variable and export the WV2 as variable called "data"
Create an ROI of a variety of deep ocean areas
In the ROI tool dialog, select File->Subset data via ROIs
In the main ENVI toolbar click File-> Export to IDL variable and export the subset as variable called "samples"
At the ENVI> command prompt in the IDL workbench, type
```
.r <path to>\<script>.pro
```
i.e
```
.r C:\Temp\deglint.pro
```
After the script completes you can get the image back into ENVI using File-> Import from IDL variable (select the "out" variable)

Thanks again for your valuable input in regards to this matter... I preformed the procedure that you recommended, sadly i got the following error:


% Syntax error.
ENVI> .r C:\Temp\Glint.pro

foreach b, bindgen(6) do begin
         ^
% Syntax error.
  At: C:\TEMP\Glint.pro, Line 12
% 1 Compilation error(s) in module $MAIN$.

What's your take on this?

Works for me.

I just realised I left in some code I shouldn't have. Try the below (also attached):.

nirs=samples[*,*,7]
nird=data[*,*,7]
d=size(nirs,/dim)
i=where(nirs gt 0)
o=where(nird eq 0)
m=min(nirs)
out=0
help, m

foreach b, bindgen(6) do begin

    band=samples[*,*,b]
    r=linfit(nirs,band)
    band=data[*,*,b]
    deglint=long(band - r[1] * (nird - m)+0.5) 

    deglint=0
    if size(out, /n_dimensions) eq 0 then                 $  ;Image stack doesn't exist yet
      out=temporary(deglint)                                 $
    else                                                  $  ;Concatenate image to stack
      out=[[[temporary(out)]],[[temporary(deglint)]]]

endforeach

out=[[[temporary(out)]],[[data[*,*,6]]]]
out=[[[temporary(out)]],[[data[*,*,7]]]]

end

An example using the above code:
Before
[ATTACH=CONFIG]11237[/ATTACH]

After
[ATTACH=CONFIG]11238[/ATTACH]

Thanks again lpinner, I'll give it a go and let you know how it goes... BTW, from your experience, the three methods that you shared with me, which did you prefer? in terms of results?

I know the IDL looks to be the easiest of them all...

What three methods? I only recall two. Both the "cookbook" method and my IDL code implement the algorithm detailed in the paper by Hedley et al. (2005) that I linked to.
I have not used the "cookbook" method. But it should give the same results, it's doing the same thing.

By the way... if you have any land in your image, this method will make it look terrible. As is noted in the paper:

the algorithm is valid only for submerged pixels

.

Screen Shot 2022-03-28 at 09.40.39.png

Ahh, i see, well that's good to know... but sadly yet again it didn't work,even with the file that you gave me...

foreach b, bindgen(6) dobegin
         ^
% Syntax error.
  At: C:\TEMP\deglint.pro, Line 10
% 1 Compilation error(s) in module $MAIN$.
% No valid main program present.

BTW, i have attached a photo of what the area I'm dealing with looks like...

[ATTACH=CONFIG]11246[/ATTACH]

So i guess I'm good, since there isn't much land, except for that narrow strip... BTW, does this image look to you beyond reparable?

10DEC18073841-M2AS-052637467020_01_P001-BROWSE.JPG

That's a different error to your previous post. Are you typing it in or copying it? There should be a space between "do" and "begin".

I copy and pasted it, well it seems that even if i used a space between "do begin" it still doesnt work... maybe there is a problem with the isntallation of the program... ill try and reinsatall the software and see how things go from there... BTW, thanks for all the help that you gave...

What version of ENVI do you have? You could also try (after opening the image in ENVI, selecting the ROI, exporting variables etc...) in the IDL Workbench, create a new file, paste my code in, save it and then click compile then click run.

Im using Envi 4.7... I'll it again and see what i get...

lpinner,
Love the script. Got it working on my second try but I have some questions. I am looking at the output data and it seems that the map info(projection,datum,etc.) is stripped away. I'll admit I am new to IDL and ENVI (in fact before someone pointed out your script I was writing a script of my own in perl). Looking through your code it looks like the map info is lost at line:

nird=data[*,*,7]

and never added back in.

Am I reading this right? Is there a way to add this data back in after the calculations are completed like you did for bands 7 & 8?

IDL doesn't use ENVI georeferencing. The map info is lost from the time you export the data to IDL arrays. Just right click on the layer in the available bands window after you import the deglinted array back into ENVI, edit the header and import the header from the original glint affected image.

Hello, been a while... so here's the update... In the end the IDL didnt work... which is kinda a downer.. but i think i figured something out in the process that i would like to share in order to determin if its legit or just my imagination...

You know in Envi it got this "relative water depth" wizard, so when i used it, it generated three files, and one of them was a RGB file, the when displayed, it kind of shows that the glint has be processed... does this mean that the glint is gone?

the down part is that its an RGB, and the total benifit of having an 8-band is gone... so still working on it trying to figure it out...

On another note...

Lets assume that for a moment that it did work.. and one of the files generated by envi is from using the "relative water depth" wizard is actually the water depth that i want to use... and from another source i got a marine survey done with coordinated depths... is there a way in ArcGIS to do an interpolation where i link the sampled water depths with the whole image in order to figure out the rest?

Hi Luke,

I've managed to run the script, however, my results aren't anywhere close to useable. My question is: did you use your raw imagery or have you converted the data to radiance, or reflectance?

Cheers

Luba

Both raw and radiance (output as integer with scale factor of 1000, standard ENVI WV2 radiance calculation).

Here's one done with integer radiance values, top is glint affected, bottom is same region following deglinting:
[ATTACH=CONFIG]12916[/ATTACH]

I've updated this script (see attached) to run from an ENVI menu item. From the readme file:

Reference:
    Hedley, JD, Harborne, AR and Mumby PJ (2005)
    Simple and robust removal of sun glint for mapping shallow-water benthos
    International Journal of Remote Sensing 26 (10), pp 2107�??2112.

Notes:
    If you have any land in your image, this method will make it look terrible.
    As is stated in Hedley et al. (2005): "the algorithm is valid only for submerged pixels".

    Only run this tool prior to pansharpening as:
       a. It loads the entire image into memory
       b. It will take a lot longer...

Installation:
   Copy deglint.sav to the ENVI "save_add" directory:

ENVI 4.8:
- Windows: C:\Program Files\ITT\IDL\IDL80\products\envi48\save_add\
- OSX: /Applications/itt/idl/idl80/products/envi48/save_add/
- *Nix: /usr/local/itt/idl/idl80/products/envi48/save_add/

ENVI 5.0 (Classic):
- Windows: C:\Program Files\Exelis\ENVI50\classic\save_add\
- OSX: /Applications/Exelis/ENVI50/classic/save_add/
- *Nix: /usr/local/Exelis/ENVI50/classic/save_add/

   Next time you start ENVI 4.8 or ENVI 5.0 (Classic) there will be a "Deglint" tool in the Spectral menu.

Usage:
   Start ENVI 4.8 or Envi Classic 5.0, open and display the image you want to deglint. Start the ROI tool and define an ROI containing a number of samples of areas of deep water. Select the "Spectral"->"Deglint" menu option and follow the prompts.

Thanks lpinner, once i got an email that there was a new post i got all excited, especially to try out this new tool... I'll give it a shot and let you know how it turns out... BTW, does it work on 4.7 or just 4.8 & 5.0?

Sorry, I don't know. It's only been tested on 4.8/5.0 so it may not run on 4.7 especially since you had issues running the original code on 4.7.

Hey, installed it on 4.8 and the following happened...

So i opened my file and selected my ROI for deep water:
[ATTACH=CONFIG]19008[/ATTACH]

And went ahead with the rest of the inputs:
[ATTACH=CONFIG]19009[/ATTACH]

However, when i pressed ok the following happened following with a complete software shutdown:
[ATTACH=CONFIG]19010[/ATTACH]

Any thoughts?

You're trying to run it in ENVI. The script only works in ENVI+IDL.

This one runs in ENVI runtime (attached)

Hey, it worked, both of them... about the results were the first four bands where completely white, and then the 5th and 6th did show something, while the last bands where completely gray, couldn't make a composite out of the results because nothing shows... I'll fiddle with the histogram and see what i can get..

I didn't bother building in any "pretty display" code.

When I run the script on radiance values (standard ENVI Worldview 2 radiance calculation) I get the following displayed:
[ATTACH=CONFIG]19135[/ATTACH]

But simply stretching the display (enhance menu) the image displays fine:
[ATTACH=CONFIG]19136[/ATTACH]

Running the script on raw digital numbers (Digitalglobe IMD format, TIFF or ENVI format) I get the image displaying ok (if a little washed out) first time.

Not a big deal, I prefer to control the display stretch myself anyway.

The band you specified as the NIR band is output as grey as the sampled data (always NIR band) is regressed against each band and when this is done for the NIR band (i.e same values), the slope will always be 1.

Note I get better results using band 7 than band 8 for deglinting Worldview2.

Hello!
Anyone knows how to apply this code for a Quickbird image?

Thanks!

Exactly the same way. Define ROI, run the tool and follow the prompts. NIR is band 4 for Quickbird imagery.

Thank you!
Thats what I thought, but I get this error
% Compiled module: $MAIN$.
% Attempt to subscript SAMPLES with <INT ( 4)> is out of range.

Hello again,

About the error I have, if I change the band number to a 3 instead of a 4 (for Quickbird), the code starts, although I get another error:
M FLOAT = 1.00112e-005
% Unable to allocate memory: to make array.

Therefore, I guess its also a problem with band number 4.

Im new using envi, so I have no much experience. Thank you, your help is highly appreciated.

Emmanuel_OppongAfriyie

@Luke can this be used for aerial images that has online RGB bands..

Emmanuel_OppongAfriyie

The image has only Red-Green -Blue Band...

mosaic of several images into an orthophoto.

Then this method will not work. It requires a NIR band.

Emmanuel_OppongAfriyie

Would you have an idea which method is more appropriate for such image without NIR.

Thanks

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