Laser-stimulated fluorescence of graffiti

[Andy Perrin]

I've had a project running for a year or so on using Laser-Stimulated Fluorescence (also called Laser-Induced Fluorescence) to allow imaging of fluorescence of large objects and areas, including doing it in the presence of streetlights. The eventual hope is to use it on the ghost signs (faded signs painted on brick buildings) to bring out faded paints.

 

Previous discussion of the topic can be read (in order) here

 

On Laser-Stimulated Fluorescence:

 

Intro to LSF and safety discussion (START HERE)

https://www.ultravio...ce-first-tests/

 

Laser-Stimulated Fluorescence of a Pumpkin (application of the above to a pumpkin)

https://www.ultravio...e-of-a-pumpkin/

 

On using image subtraction to remove street light from UV fluorescence images:

 

Queen Anne's Lace, UVIVF w/ "Nemo," Noise-reduction Stacking

https://www.ultravio...ction-stacking/

 

Tree stump UVIVF with contaminating light removal by image subtraction

https://www.ultravio...ge-subtraction/

 

New results, using graffiti as a test subject

 

Equipment:

- Sony A7S camera (converted, with Bayer)

- Micro Nikkor 55mm/2.8 AI-S lens

- Omega light pollution filter (to attempt to reduce the streetlights...not very effective) + Tiffen Haze 2E filter to block the laser

- 405nm violet 900mW laser, equipped with a 30 degree Powell lens (nominal power rating, not verified)

 

The scene in daylight, shot with iPhone

 

The scene in darkness with no laser, but with the above two filters (camera was A7S):

 

The scene after alignment, image subtraction and brightness/contrast adjustment (with laser - no laser = fluorescence)

 

The images were not stacked, but I did apply denoising afterwards with Neat Image in Photoshop.

[Andrea B.]

Excellent technical result, Andy. You are doing some cutting edge work for sure! And it is always interesting.

 

That last photo is way cool -- both weird and artistic at the same time. It appears as though the cyan letters are floating above the bricks.

 

((The laser induced fluor pumpkin linked above is one of my absolute faves !!))

[Andy Perrin]

Thanks, Andrea!

[Doug A]

I've had a project running for a year or so on using Laser-Stimulated Fluorescence (also called Laser-Induced Fluorescence) to allow imaging of fluorescence of large objects and areas, including doing it in the presence of streetlights. The eventual hope is to use it on the ghost signs (faded signs painted on brick buildings) to bring out faded paints.

 

Previous discussion of the topic can be read (in order) here

 

On Laser-Stimulated Fluorescence:

 

Intro to LSF and safety discussion (START HERE)

https://www.ultravio...ce-first-tests/

 

Laser-Stimulated Fluorescence of a Pumpkin (application of the above to a pumpkin)

https://www.ultravio...e-of-a-pumpkin/

 

On using image subtraction to remove street light from UV fluorescence images:

 

Queen Anne's Lace, UVIVF w/ "Nemo," Noise-reduction Stacking

https://www.ultravio...ction-stacking/

 

Tree stump UVIVF with contaminating light removal by image subtraction

https://www.ultravio...ge-subtraction/

 

New results, using graffiti as a test subject

 

Equipment:

- Sony A7S camera (converted, with Bayer)

- Micro Nikkor 55mm/2.8 AI-S lens

- Omega light pollution filter (to attempt to reduce the streetlights...not very effective) + Tiffen Haze 2E filter to block the laser

- 405nm violet 900mW laser, equipped with a 30 degree Powell lens (nominal power rating, not verified)

 

The scene in daylight, shot with iPhone

 

The scene in darkness with no laser, but with the above two filters (camera was A7S):

 

The scene after alignment, image subtraction and brightness/contrast adjustment (with laser - no laser = fluorescence)

 

The images were not stacked, but I did apply denoising afterwards with Neat Image in Photoshop.

 

Very interesting work and results. So many of these signs were painted on brick walls. You are doing a great job bringing the history back to life.

 

The pumpkin is cosmic.

 

Thanks for sharing,

 

Doug A