yellow and green black and white

[sgwrx]

so i find myself adjusting yellow quite a bit in both black and white  and color images.  i do this, and have always done it, to adjust my greens in the image.

lets use photoshop as an example.  it has a sensitivity slider for yellow.  if i pull that down, the green grass in my image will become darker.  if i pull that up my green grass will become lighter.

in non-digital photography, what type of filter would someone put on the camera to get darker green grass and why?  a filter screwed onto the lens would do what? increase sensitivity in the color of the filter or decrease it?  or are filters colored and named differently - for example would you refer to a filter who's physical color is yellow to a "green" filter?

i hope this makes sense. not sure this is the right forum for the post for various reasons.

thanks,

[Eric Myrvaagnes]

In (Black-and-white) film photography either a green filter or a yellow filter would make grass look lighter, because what we see as "grass green" does have a considerable amount of yellow in it. The effect on typical evergreen foliage would be less, because that green has less of a yellow component.

When converting digital scenes to B&W in Lightroom, I often find that the yellow slider has more effect on an area that looks green to me than the green slider does.

A colored filter on a camera lens decreases sensitivity to colors that aren't transmitted by the filter. Thus, a red filter is used to darken blue skies, and a blue filter increases the sense of haze in distant scenes.

So, your question does make sense (at least to me.) I hope this helps.

[Peano]

Discussion of filters here.

[Eric Myrvaagnes]

Discussion of filters here.

That's a very good and clear discussion.

[sniper]

Orange or red filters on the lens will make the grass darker, but it will affect other colours as well (make reds lighter, blues darker ect)
Most digital cameras have built in filters for black and white, usually in the user setting for the different profiles like landcsape and vivid.  I have a profile set up on one camera I use for black and white a lot, but to be honest I mostly do it PP in silvereffx.

[Eric Myrvaagnes]

I agree that for digital black and white it is better not to use filters on the camera. The controls you have in software (Lightroom, Silverefx, etc.) let you experiment and see exactly what the varying amounts of "digital filters" can do to all the colors in a scene.

[sgwrx]

thanks.  great link too!