Letter reflection from beer can

[nmsurobert]

TL;DR Summary

I was sitting outside drinking and noticed that the color of reflection of the white letters and black outlines was inverted in the shadow. The green makes sense, but I don't under understand the other two I've been trying to explain it to myself but I've had no luck. Google has been no help either.

 

[berkeman]

https://www.memesmonkey.com/images/memesmonkey/7f/7fdc86d1052905ae31f0a2e0599a606f.jpeg

But seriously, this is a can or a bottle? Which way is the Sun illumination coming from? What are we looking at? (Diagram of your beer setup is needed...)

 

[nmsurobert]

View attachment 301171
https://www.memesmonkey.com/images/memesmonkey/7f/7fdc86d1052905ae31f0a2e0599a606f.jpeg

But seriously, this is a can or a bottle? Which way is the Sun illumination coming from? What are we looking at? (Diagram of your beer setup is needed...)

It's a can. The can is facing west and the sun is in the east.
The shadow is being cast by other beers that have been consumed.

 

[phinds]

Clear as mud

 

[berkeman]

It's a can. The can is facing west and the sun is in the east.
The shadow is being cast by other beers that have been consumed.

Um, cans are opaque...

 

[nmsurobert]

Um, cans are opaque...

That doesn't explain anything to me lol. I've tried this with different cans since I first saw this a few weeks ago. And sometimes white letters make white reflections but other times white letters make black reflections.

 

[hutchphd]

Strangely this does not seem to be a case of Beer's Law...
Seriously list all illuminants and the relative geometry to all salient objects

 

[berkeman]

sometimes white letters make white reflection but other times white letters make white reflections.

Yeah, I can see how that would be confusing...

 

[nmsurobert]

Am I being trolled right now?
I figured there would be some physical explanation this.

 

[berkeman]

The Mentors are still trying to figure out who is being trolled in this thread.

Post a clear diagram and many more pictures of the setup and images if you want a serious answer. I'm drinking wine anyway...

 

[berkeman]

And you might want to correct your typo that I pointed out in my post #8. Assuming that it was indeed a typo...

Lordy.

 

[nmsurobert]

The set up

The lettering on "Pale Ale" is white outlined in black.

The reflection of the letters "pa" and every other letter cast in the shadow is black. And the outlines are reflected in white.

 

[hutchphd]

That's better.
When you look at the can, you are seeing diffuse reflectance from the can to your eye.
When you look at the projection in the shadow, that light is diffusely reflected from the floor after being initially specularly reflected by the can surface.
The diffuse reflectance from a surface can be very different than the specular: most often this is due to local roughness and pigment particle size. The white pigment does not reflect the specular strongly but does reflect diffusely well.
I used to be an expert at this when I designed reflectance based medical instruments.

 

[nmsurobert]

That's better.
When you look at the can, you are seeing diffuse reflectance from the can to your eye.
When you look at the projection in the shadow, that light is diffusely reflected from the floor after being initially specularly reflected by the can surface.
The diffuse reflectance from a surface can be very different than the specular: most often this is due to local roughness and pigment particle size. The white pigment does not reflect the specular strongly but does reflect diffusely well.
I used to be an expert at this when I designed reflectance based medical instruments.

How interesting. I never would've thought of diffusion. Thank you! That makes sense now.

 

[hutchphd]

How interesting.

Thanks for the good question!

 

[sophiecentaur]

How interesting. I never would've thought of diffusion. Thank you! That makes sense now.

I would add that there are probably areas of shiny / specular paint surface which will do the equivalent (laterally inverted) of cut out holes, which would form images on the other (shady) side of the can. The reflection shadows will be pretty sharp because the distance to the table top is short.

I'm not sure that diffuse reflections are likely to form sharp images; it would be 'out of character', imo. Such diffuse images would tend to fill up the sharper images and reduce contrast.

 

[hutchphd]

I'm not sure that diffuse reflections are likely to form sharp images; it would be 'out of character', imo. Such diffuse images would tend to fill up the sharper images and reduce contrast.

The highly diffusely reflective (white) letters appear bright on viewing directly because they profligately squander this incident solar flux in all directions leaving little for specular reflection. The black letters are more mirror-like and actually produce more specular intensity.
Remember this is outside and the specular reflected collimated sunlight dominates the "ground" image.