bmattock
Veteran
Another Way to Look at Color Filters
I think we tend to get confused about the use of color filters for B&W because the descriptions we read don't address some underlying assumptions which are incorrect. So I was trying to think of a way to present an explanation of color filters that makes sense. This explanation assumes properly-exposed and developed film to begin with.
I think the basic problem is that we think of B&W film as if it were just 'desaturated' color film, and it is not. Color prints say that white things are white - black things are black. Blue is blue, and so on. Is this not also true of B&W film, at least for the 'white' and 'black' things?
B&W film does not record black as black and white as white. What? That's right, B&W film does not know what white is, or what black is. It records only shades of gray based on a sliding scale of relative brightness. Everything is on a sliding scale of relative brightness - the brightest is white, the darkest is black. Everything else is a shade of gray.
What I mean by that is this - in any scene, B&W film records the lightest shade present as 'white' and the darkest as 'black'. Everything else gets a shade of gray, based on it's relative brightness compared to everything else in the scene.
Now, knowing this - if we use a color filter to increase the RELATIVE brightness of a particular color, then everything of that color gets bumped up the scale of relative brightness - it becomes 'lighter' in shade. If it becomes the brightest light in a scene we're photographing, then it gets recorded as white.
The film is recording LUMINANCE, not B&W RENDITIONS OF SHADES OF GRAY. Luminance is brightness - not color, not shade, not tone. Brighter is whiter with B&W film.
For example...imagine a flower bed. Green leaves and red flowers, in this simple case. With straight B&W film and no filters, both the shade of green and the shade of red present may have the same relative brightness - the same luminance - so they will be recorded as the same shade of gray. This may not be what we want.
So, how do we change it? Well, if we put a red filter on our lens, then we are passing more red light and blocking green. Red things move up the chain of relative brightness - and are recorded as 'whiter' than green things, which move down and are recorded as 'darker' than they otherwise might be. If the red flowers are now reflecting the most light in the scene, they record as 'white' on our B&W film. All we are doing is changing the RELATIVE POSITION of the red versus the green by applying a filter so MORE red than any other color gets through.
The same thing happens in reverse if we put a green filter on our lens. The leaves, being green, are now brighter and therefore a lighter shade of gray than the red flowers, which become darker.
With that said, it is easy to understand what the most common color filters are good for - manipulating relationships among colors.
Colored filters lighten their like - and darken their opposite (called their compliment). So red filters make blue skies dark and ominous, yellow filters less so. Green filters block red - and so can have a positive effect on caucasion skin tones in out-of-doors portraits where red or pink blotches and uneven reddish skin tones are common. However, it will darken red lipstick to almost black, and so will have a heavy effect on a portrait of a woman wearing it.
Here is a good resource:
http://www.schneideroptics.com/filters/filters_for_still_photography/black_&_white/
I think that should do it. However, by way of passing, I'd also like to address a couple of common questions about the use (or need for) color filters:
1) Can you use color filters on digital cameras? Maybe. Some work, some get confused. Some that can be put in 'B&W mode' are probably more likely to work than those that cannot.
2) Can you just use Photoshop later on to duplicate the effect of a color filter? Yes, if you shot in color originally. If you shot in B&W, or if the image has already become desaturated to B&W, then the individual color information does not exist - you cannot duplicate the effect of say, a red filter, when everything is shades of gray. What's red? What's green? The image no longer contains that information.
3) Do you 'need' to use color filters? No, not in most situations. It is merely another creative option. It is interesting because it allows us to make more distance between colors that would otherwise render as similar shades of gray, which can serve to highlight or isolate a subject in a photo and make an otherwise boring B&W photo 'pop'. Continued overuse of the same filter effects can become tiresome, however. A heavy dark foreboding sky rendered with a dark red filter is cool - but after a couple hundred of them, one begins to feel the need for a visit to the beach.
I hope this is helpful.
Best Regards,
Bill Mattocks
I think we tend to get confused about the use of color filters for B&W because the descriptions we read don't address some underlying assumptions which are incorrect. So I was trying to think of a way to present an explanation of color filters that makes sense. This explanation assumes properly-exposed and developed film to begin with.
I think the basic problem is that we think of B&W film as if it were just 'desaturated' color film, and it is not. Color prints say that white things are white - black things are black. Blue is blue, and so on. Is this not also true of B&W film, at least for the 'white' and 'black' things?
B&W film does not record black as black and white as white. What? That's right, B&W film does not know what white is, or what black is. It records only shades of gray based on a sliding scale of relative brightness. Everything is on a sliding scale of relative brightness - the brightest is white, the darkest is black. Everything else is a shade of gray.
What I mean by that is this - in any scene, B&W film records the lightest shade present as 'white' and the darkest as 'black'. Everything else gets a shade of gray, based on it's relative brightness compared to everything else in the scene.
Now, knowing this - if we use a color filter to increase the RELATIVE brightness of a particular color, then everything of that color gets bumped up the scale of relative brightness - it becomes 'lighter' in shade. If it becomes the brightest light in a scene we're photographing, then it gets recorded as white.
The film is recording LUMINANCE, not B&W RENDITIONS OF SHADES OF GRAY. Luminance is brightness - not color, not shade, not tone. Brighter is whiter with B&W film.
For example...imagine a flower bed. Green leaves and red flowers, in this simple case. With straight B&W film and no filters, both the shade of green and the shade of red present may have the same relative brightness - the same luminance - so they will be recorded as the same shade of gray. This may not be what we want.
So, how do we change it? Well, if we put a red filter on our lens, then we are passing more red light and blocking green. Red things move up the chain of relative brightness - and are recorded as 'whiter' than green things, which move down and are recorded as 'darker' than they otherwise might be. If the red flowers are now reflecting the most light in the scene, they record as 'white' on our B&W film. All we are doing is changing the RELATIVE POSITION of the red versus the green by applying a filter so MORE red than any other color gets through.
The same thing happens in reverse if we put a green filter on our lens. The leaves, being green, are now brighter and therefore a lighter shade of gray than the red flowers, which become darker.
With that said, it is easy to understand what the most common color filters are good for - manipulating relationships among colors.
Colored filters lighten their like - and darken their opposite (called their compliment). So red filters make blue skies dark and ominous, yellow filters less so. Green filters block red - and so can have a positive effect on caucasion skin tones in out-of-doors portraits where red or pink blotches and uneven reddish skin tones are common. However, it will darken red lipstick to almost black, and so will have a heavy effect on a portrait of a woman wearing it.
Here is a good resource:
http://www.schneideroptics.com/filters/filters_for_still_photography/black_&_white/
I think that should do it. However, by way of passing, I'd also like to address a couple of common questions about the use (or need for) color filters:
1) Can you use color filters on digital cameras? Maybe. Some work, some get confused. Some that can be put in 'B&W mode' are probably more likely to work than those that cannot.
2) Can you just use Photoshop later on to duplicate the effect of a color filter? Yes, if you shot in color originally. If you shot in B&W, or if the image has already become desaturated to B&W, then the individual color information does not exist - you cannot duplicate the effect of say, a red filter, when everything is shades of gray. What's red? What's green? The image no longer contains that information.
3) Do you 'need' to use color filters? No, not in most situations. It is merely another creative option. It is interesting because it allows us to make more distance between colors that would otherwise render as similar shades of gray, which can serve to highlight or isolate a subject in a photo and make an otherwise boring B&W photo 'pop'. Continued overuse of the same filter effects can become tiresome, however. A heavy dark foreboding sky rendered with a dark red filter is cool - but after a couple hundred of them, one begins to feel the need for a visit to the beach.
I hope this is helpful.
Best Regards,
Bill Mattocks
