Color Perception

[FrankG]

Check out this neat optical illusion website.

eChalk: Colour perception

www.echalk.co.uk

Check out both Colour perception and Colour perception 2
(Colour? Well, it does have UK in the url, so that explains that...)

I spent quite some time looking at them. Some of them are hard to believe, and in fact in a few cases I had to really study them to convince myself they're not tricks. Amazing what a difference adjacent colors can make.

Think this silliness has nothing to do with Photography? Think again, the same exactly thing happens in your photos!

 

[BobH]

Frank,

Thanks for posting that link. I've seens those before, and they're really neat.

For photographers, they're more than just a party trick. They're also a lesson in light and color balance.

The adjacent colors can have a real effect on the apparent colors in your image. In one illustration, the yellow and blue overlays dramatically effect the color of the piece in the center of the X. In the blue scene, it appears bright yellow. This effect is rather persistent, and remains even as you reduce the blue tint.

How does this effect photographers? It's a good simulation of white balance. The yellow is similiar to the tone you get from Incandescent lights, a warm glow, while the blue is what you see from many Flourescents lights. If your camera is set on auto white balance, and you're under flourescents, you may end up with a yellow cast to everything in your shot. The grey piece in the center appears fairly close to a standard grey card, even though it looks to be bright yellow at times.

That shows you how important white balance really is. You should be doing something to make sure you get white balance correct, whether that be using a grey card, setting your cameras white balance using one of the custom white balance settings, setting it using the Kelvin scale on higher end cameras or adjusting it after the fact if you're shooting in raw. Exactly how you do it isn't as important as whether or not you do it. If you don't, you can end up with people who look like they've got yellow fever, or are a sickly shade of grey.

That's also why the gallery is done in all grey, instead of some other color. The grey was deliberately chosen to have the least possible effect on the images. The blue that we use here in the forum would make the images look cooler (as in temperature, not in "hipness") while a yellow or red would make them look warmer. Since I don't want to change the tone of an image, I chose grey to try and avoid any influence.

 

[Leia]

....setting your cameras white balance using one of the custom white balance settings, setting it using the Kelvin scale on higher end cameras

My latest challenge is white balance with strobe lighting. I am finding oddities in auto WB with the strobes that I don't get in outdoor or others situations. How do you set it for strobes? The modeling lights I keep on are nothing like the strobes. They are dimmer and less 'white'.

ANY suggestions or tips on this would be greatly appreciated.

I have an XTi and can adjust WB manually....just don't know where to start.

 

[BobH]

Leia,

Do the strobes you're using have a temperature listed?

My Nikon strobes are rated for 6000 Kelvin. I use the Nikon Creative Lighting System, and I must say it works great. I don't think I've ever had much need to adjust my flash photos.

Are you solely using strobes, or is there also ambient lighting? That can throw things off.

Here's what happens. Let's say the ambient lighting is flourescent, which has a decidely blue tint to it. Now you add in your flash, which does not have any tint to it, but instead is pure white. When you correct for the blue tint from the ambient, you also shift the pure white light, making it too yellow. (Does that make sense?)

They've got a solution for that. They provide gels, which tint the light from your flash. Sounds like it would just make more problems, but what you do is make everything have the same shade, for example a blueish tint, then when you correct it all shifts to white.

I'm guessing you've already tried the flash WB setting on your camera, or does it have one? What happens when you use that? Can you post a sample, maybe of something white so it's easy to see the tint. Also, are you shooting in raw?

 

[Leia]

Sheesh...you'd think the kits would come with instructions.

I will check the temps and adjust accordingly. When you speak of ambient light, are you including the light from the soft modeling lights?

 

[BobH]

Leia,

I started to reply and discoverd all my store scripts are broken... ugh!

Back later.

 

[BobH]

Sheesh...you'd think the kits would come with instructions.

Yes, that would be nice. The problem is that flashes, at least complicated ones like the Nikon Creative Lighting System, take a lot of explaining.

Here's a book that I use, and really like, for the Nikon stuff. I seem to recall that you use Canon, but maybe you can find a simliar one.

http://www.railroadbookstore.com/ph...tive-Lighting-System-Digital-Field-Guide.html

It has over 200 pages of explanation, starting with the real basics, how to set your flash up, what all the buttons do etc. and goes into the complex things like remote flashes and groups etc. Great reference!

I will check the temps and adjust accordingly. When you speak of ambient light, are you including the light from the soft modeling lights?

Any light that's visible in the shot will have an effect. However, the softer it is, the less it will affect the image.

Think of it this way. You've got a white piece of paper, and I'm shining a soft yellow light on it. There's also a bright white light on it. The dim yellow will still add a gentle tint, right?

So you correct for the yellow, by adjusting the white balance. Now the paper looks white where it was yellow. But where it was white before is now a light blue. Subtle, but noticable, especially on skin colors. (I think it would get a blue tint, I could be wrong in which direction the color will shift, but you get the idea, and the important concept is that it will shift, rather than exactly what color it ends up being...)

In post processing, the image can't distinguish between any of the light sources. So you try hard to make them all have the same temperature, then either set your white balance for that, or shift accordingly in post.

I'm guessing the easy way to start correcting would be to use a tried and true grey card, and set a custom white balance to that, and see what kelvin reading it shows. Then set your other photos to match and see how they look.