Foul blue LED lights

Last week we went to see a literary discussion. The hosts wore red, and the stage was well lit. However, someone decided to also add blue LEDs, because you can’t have a stage without blue LEDs, right?

In the image below, the LEDs are partly blocked – it’s pretty easy to see on the man’s shirt, as well as on the curtain behind the lady, where her shadow colours the curtain yellow.

2023-03-10_19-12-33_P1080015.RW2 (11.5 MB)

One attempt to fix the abrupt transition on the shirt:

2023-03-10_19-12-33_P1080015_01.RW2.xmp (10.9 KB)

Here’s the camera’s rendition (underexposed to protect the highlights):

For reference, here’s a shot from another angle, which I was able to correct more:

It’d be nice to have some colour on the lady’s skin. The man’s beard is not so bright white, either; and he’s not completely grey. Here’s an official photo of them (without blue LEDs…):

What’s your take?

These files are licensed Creative Commons, By-Attribution, Share-Alike.


Man, that’s really a bad one. (wish we had something as a noise-cancelling light source :slight_smile:

I would simply forget the color and go for black&white …

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I did B&W, and it turned out quite well; I like the atmosphere. Here I’m interested in the colour, though. :slight_smile:

This is an interesting one to play with and have opinions about…

My take: There’s no need to drastically remove or “fix” the blues. There’s a lot of it in the scene and this will have been visible at the time. The shadow of the partially blocked blue light would also have been visible. If the goal is to create an RGB neutral result from this image you’re in for a bit of a challenge.

Anyway, this is my quick take in RawTherapee:

EDIT: With István’s below remark about the scene actually not being all that blue in reality, I tweaked the above one a bit:

rt5.9 dev + pr6641

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The trouble is, it did not look so badly blue at the scene. The stage looked rather neutrally lit.
Anyway, would you mind to share your sidecar? RT gave me this as the default:

After picking WB, everything turns too yellow:

Or too blue:

But I have not used RT for years, so no wonder I cannot get good results with a simple WB adjustment.

2023-03-10_19-12-33_P1080015_02.RW2.xmp (18,5 KB)


Sure, although there is a caveat: This one uses the not-as-yet implemented Tone Equalizer. Guessing here that you are computer tech-savvy enough to merge that one.

Here you are: RawTherapee 5.9 dev + #6641

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Thanks. A gh pr checkout 6641 should do it, right?


PM-ed you about merging.

Tricky one. Used the official picture as a reference for spot color correction measurement. Then mostly desaturated blue channel and increased contrast, but the result is by no means perfect.

20230318_0001.RW2.xmp (44.6 KB)

P.S.: Boris, well done on your effort! I learned 90% of my darktable skills from your videos, anyway.


Nice ! I am quite impressed by what you achieved with Color Calibration module.
Probably a matter of taste, but I would add a little bit more saturation and a tiny bit warmer color balance. So based on your edit, here my take :

2023-03-10_19-12-33_P1080015.RW2.xmp (24.3 KB)

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My interpretation with dt 4.2.1:

  1. I keep the blue color of the water bottle without masks.
  2. In the color calibration I have used the “spot color mapping” correction on the blue of the led.
  3. With “Color look up table” I reduce the saturation of the green.

    20230317_0083.RW2.xmp (9,0 KB)


Extremely difficult! My best attempt so far in GIMP.

This was a real challenge! I feel that since the blue lights were there, there is no need to remove them completely. It’s more about taming them.
darktable 4.2.1:

2023-03-10_19-12-33_P1080015.RW2.xmp (23.9 KB)

Thanks. This looks very strange, though. For example the shadows are much brighter than the illuminated surfaces. Check the area around the man’s trousers, as well as that to the (picture-)right of the lady’s knee, or below where her dress falls from her leg.

Compare those areas with e.g. Foul blue LED lights - #10 by firefrorefiddle

I agree! It is the best I have achieved so far after numerous tries.

My version…

2023-03-10_19-12-33_P1080015.RW2.xmp (17.8 KB)

2023-03-10_19-12-33_P1080015.RW2.xmp (8.7 KB)


Darktable 4.2.1 2023-03-10_19-12-33_P1080015_01.RW2.xmp (17.8 KB)


That’s not surprising, and has nothing to do with your skills: you have a situation with mixed lighting, where different parts of the scene have different illuminants. You cannot “modify” all those illuminants with one white balance setting…