View Full Version : Sample reflectivity profile
ahmadr
05-19-2007, 01:06 PM
This is at ~400mm equivalent zoom.
Rightmost part of plate is covered with matt tape (~=lasershield).
The circles around the turn indicators are 100% flat. The one on the left side of the picture is bright, showing I am exactly perpendicular to it. I took many pictures, and this one had the most reflection from the headlights (worst case scenario).
Notice the grill has a chrome surround, but is not reflective since it is slightly angled.
For reference:
Conclusion: Take a picture at night and at max zoom (perpendicular of course), to SEE what a lidar would see. In this case, even with protection, the front plate is brighter than the headlights (even in worst case conditions).
I wonder how the picture would have turned out if the car was silver / white.
For photography lovers, set the shutter speed to the maximum flash sync supported by your camera to reduce light from sources other than your flash. 1/500 sec in this case.
Phillip559
06-06-2007, 07:47 PM
I"m not an expert of this Ir light reflectivity stuff but I'm willing to say if you veiled the lights and license plate that car would be super stealthy. i dont see any relfection. Lucky you!
ancientintegra
08-06-2007, 06:27 PM
Conclusion: Take a picture at night and at max zoom (perpendicular of course), to SEE what a lidar would see.
Not to be nasty, but this is not a good way to see what LIDAR would see, unless there is something about the illumination that you are not saying. Veil blocks the wavelength of police LIDAR somewhat selectively, so unless you are measuring reflection of 904 nm light, you are not getting the right impression.
Also, cameras and the human eye are very non-linear and context sensitive in their response to light*, so even if the photo is accurate it is not a good way to tell. The best way to tell is to use a spectrophotometer as I and others here have done. This gives you a reliable measurement of the attenuation of the exact wavelength of light that matters.
*There are numerous optical illusions that capitalize on this phenomenon. For example:
http://www.moillusions.com/2007/07/same-colored-checkers-illusion.html
Not to be nasty, but this is not a good way to see what LIDAR would see
Not to be nasty , but I agree with Amdr analysis , whatever the wavelengt , be 550 nm or 900 nm light will reflect the same way on the same surface , so one can draw the same conclusion for visible light or for infrared ...
See my full anwser here :
http://secrets.niceboard.com/Discussion-Generale-f1/-p74.htm#74
That's not true at all. Different wavelengths of electromagnetic radiation respond completely differently to different materials. Remember, silica glass is almost perfectly transparent to visible light, yet it's nearly opaque to infrared. A black metal surface will reflect radio waves, yet will absorb visible light. The only way to know how a specific wavelength will respond is to test it.
ELVATO
08-06-2007, 08:38 PM
Yea, for example:
If you were to take a picture of a black shirt under "normal" light, it looks black. Look at that same shirt in Nightshot, and it will look almost white.
ancientintegra
08-06-2007, 08:58 PM
Not to be nasty, but this is not a good way to see what LIDAR would see
Not to be nasty , but I agree with Amdr analysis , whatever the wavelengt , be 550 nm or 900 nm light will reflect the same way on the same surface , so one can draw the same conclusion for visible light or for infrared ...
See my full anwser here :
http://secrets.niceboard.com/Discussion-Generale-f1/-p74.htm#74
If you believe this, what do you think makes different objects different colors? Why is one car red and another blue?
Veil Guy
08-06-2007, 09:53 PM
ahmadr,
Way to go Ford!
Looks very appealing to me, dude.
Veil should do very well with your setup.
I know. I know, I owe you guys some high-definition before/after IR night, shots...
I haven't forgotten.
Veil Guy 8)
Veil should do very well with your setup.The one thing I would recommend, though: Get some fine grit sandpaper, painter's tape, a can of black Duplicolor, and a can of clearcoat Duplicolor, and black out that chrome grille surround. It'll give the car more of a "sport" look, and it'll get rid of the other big reflective thing on your front end.
If you believe this, what do you think makes different objects different colors? Why is one car red and another blue?
I was talking about reflectivity = the % of return of a light striking an object . What I explained is : the parts of his car that reflects his flash would be mostly identical if taken with a infrared flash .
If you look at remote imagery made by satellite you will see that some material absorbs greatly infrared , mostly plants , but on a car there are no such material : each part reflects infrared according to their own color and their finish , mat with less , glossy with high reflectivity , bright color with high , dark with less , but the rule of proportionality remains the same ...
ahmadr
08-20-2007, 09:08 AM
The one thing I would recommend, though: Get some fine grit sandpaper, painter's tape, a can of black Duplicolor, and a can of clearcoat Duplicolor, and black out that chrome grille surround. It'll give the car more of a "sport" look, and it'll get rid of the other big reflective thing on your front end.
It is reflective, but because it is angled, it is reflecting light to the stars ;)
ahmadr
08-20-2007, 09:13 AM
If you believe this, what do you think makes different objects different colors? Why is one car red and another blue?
I was talking about reflectivity = the % of return of a light striking an object . What I explained is : the parts of his car that reflects his flash would be mostly identical if taken with a infrared flash .
If you look at remote imagery made by satellite you will see that some material absorbs greatly infrared , mostly plants , but on a car there are no such material : each part reflects infrared according to their own color and their finish , mat with less , glossy with high reflectivity , bright color with high , dark with less , but the rule of proportionality remains the same ...
Exactly. The "profile" I shot assumes IR would have the same reflectivity as visible light. As long as you don't have anything targeted for IR blocking (or transmission), this is a good assumption. Furthermore, virtually all the reflection comes from inherently reflective items (lights, plate) that would certainly do the same for IR
The fact that infrared light is also reflected off the mirrors provides evidence in support of the idea that infrared light behaves like visible light.
From a Nasa site ...
http://media.nasaexplores.com/lessons/04-047/5-8_2.pdf