monochromatic filtering

hi, was hoping that you may be able to help :) if i had a white object against a green and brown background, in bright sunlight, is there a filter available to block out everything except the white object? if not what sort of filter is available to make the object to stand out further against the background?

thanks,

ted

Quote:

---

Originally Posted by ted smith

if not what sort of filter is available to make the object to stand out further against the background?

---

How about a lighting technique? I'm not the resident expert on that by any means, but check the Studio and Lighting forum here.

I don't think a filter exists to do what you're looking for. This is fairly common in the commercial world - creating ads of an object against a different background. This way you can light the product how you want and when you want (in a studio rather than counting on the weather). You can remove whatever background the shot has in Photoshop.

A polarizing filter would be my first choice for white object & bright sunlight and darker background. Depending on distance between the white object and background other methods can be used to obscure background.. Depends on type of camera also.

I'm with Another View on this one. I think a lighting change is what you need. I don't know the details of your situation, but maybe you could use a flash or reflectors to brighten the subject, thus darkening the background. I don't know of a filter that would really help.

Paul

I can't see how lighting is the problem or how any additional lighting could help since subject is white in bright sunlight(same color temp as electronic flash, 5600K)

Ted: Could yo give us more info, a pic would be great, Maybe its a situation where an overcast shot with aux lighting would be best...so so many possibilities.

thanks all for your help.

a bit more info about what i am trying to achieve. i am interested in motion tracking systems and trying to integrate a camera into some software i've written. i have been rolling a white golf ball across lawn at different speeds but the system isn't working well when the ball is rolling at slower speeds. i did a bit of research on google regarding how to make the ball stand out more against the background and monochromatic filtering seemed like a possibility. i haven't read much about polarisation but will certainly have a look in this direction. unfortunately distance from the camera lens and lighting are variables that i can't control in this instance. i would appreciate hearing your thoughts and would be happy to answer any further questions.

thanks again

ted

Hi Ted :
That doesn't sound like anything polorizing would fix. And certainly nothing I tried before.
This may be totally "off the wall" but what if your golf ball was the size of a softball or larger ?
Creating a little illusion maybe !
Interesting indeed, wish I could have been of more help.


Greg

Think subtractive.
You want to subtract green from the image and leave the white ball.
So, what colour is a "minus green" filter?

Well if you're using a colour video camera with RGB feed it's a pair of wire cutters :)
Just take out the green signal !
Of course if you're using sync-on-green that's not so good an idea, just clamp the video to black in that case and let the sync through.

Quote:

---

Originally Posted by Greggie Boy

I can't see how lighting is the problem or how any additional lighting could help since subject is white in bright sunlight(same color temp as electronic flash, 5600K)

---

Quality vs. Quantity. For example, on-camera flash tends to make everything look flat but moving the flash at an angle to the subject can make something really stand out. Take a flashlight and shine it directly at a brick wall, then put it right on the wall shining across it - big difference in how it looks. Same quantity of light but now there's a lot of texture to it.

I don't know that a polarizer would work, because the light would have to be at a 90 degree angle to the filter (the camera, of course) to get maximum effect. As the light direction varies, so will the polarization effect.

You can also increase contrast with a white subject and a dark background but you've already got that... Could you add a light at an angle (maybe 45 degrees for starters?) near where the ball needs to be picked up?

I'm guessing this is a motion camera, like something used in industrial automation. If this is the case, then the manufacturer probably has recommended light levels and tips on how to get it to work best.

First, let me just say that I don't know if this is really a photography problem, and I doubt I can help you, but being an engineer, it's in my blood to try to solve problems. I can't help but contribute to the brainstorming. :)

You could remove the green channel digitally (per the SmartWombat), or you might just try increasing the contrast in monochrome.

Quote:

---

Originally Posted by ted smith

....the system isn't working well when the ball is rolling at slower speeds.

---

I'm inferring from your statement above that the system is working when the ball is moving at higher speeds. That makes me think the color seperation (or contrast) is not the problem. Maybe it has more to do with the software algorithms than the signal? Something about the rate of change? It's hard to say with out seeing your code (and taking a bunch of programming classes).

This is interesting, so let us know if you figure something out.

Good luck,
Paul