What does a red filter do in black and white photography?

A red filter passes red and stops most blue and green. On black and white film a blue sky goes dark, near black in a deep blue, and clouds stay white; skin, lips and red things go light, and bright greens dark. It costs about three stops: Kodak and Ilford both give a daylight factor of 8 for their fast films.

What does a yellow filter do in black and white photography?

It holds back blue, so a blue sky prints a little darker and clouds stand out, about as the eye sees the scene. Panchromatic film sees blue more strongly than the eye, so with no filter skies print pale; behind a yellow filter Clack’s model of Tri-X prints blue almost exactly as dark as the eye finds it. Its factor is 1.5 to 2, one stop or less.

Which filter is best for black and white portraits?

Wikipedia calls a light yellow-green filter the standard portrait filter for panchromatic film. A yellow or orange filter lightens skin a little, orange more; a red filter lightens skin and lips a lot, which can look pale; a green filter darkens skin and lips.

Do you need color filters for black and white digital photos?

No. A digital camera records color, so the filter can be applied afterwards, in the black and white conversion: weight red up and blue down for a red filter’s sky. A JPEG saved in black and white has lost its color and cannot be filtered again.

What is a filter factor?

How many times more exposure a filter needs: 2 is one stop, 4 two stops, 8 three stops. It depends on the film’s color sensitivity and on the light, so datasheets list it per film, and sometimes for daylight and tungsten apart.

Can you use black and white filters on color film?

Not for the same purpose: a strong yellow, red or green filter tints the whole color picture. Color film uses light-balancing filters instead, such as the 81A to warm and the 82A to cool.

Is a polarizer a black and white filter?

It works on any film. A polarizer is colorless; it darkens blue sky most at about 90° from the sun and cuts reflections. Kodak gives it a factor of 2.5 on Tri-X. On black and white film a red or orange filter darkens a sky more.

What filters does Clack have for black and white?

Yellow, orange, red and green (Wratten 8, 21, 25 and 58), on its two black and white films, Press 400 and Street 400. Each is Kodak’s published filter curve through the film’s own color sensitivity, and the exposure is kept, as a meter behind the lens would.

Guide · Updated 4 November 2026

Black and white filters

Yellow, orange, red and green on the lens.

Black and white filters are colored glass filters on the lens. On black and white film a filter lightens things of its own color and darkens its opposite: a yellow filter darkens a blue sky a little so clouds stand out, orange darkens it more, and red turns it nearly black while lightening skin and red things. Green lightens foliage and darkens reds. Each filter costs light, given as its filter factor: 2 is one stop more exposure, 8 three stops.

A “black and white filter” in a photo app is something else: it turns a color photo gray afterwards, with a mix of the colors the app chose. Below: what a lens filter does and why film needs one, which filter for what, the factors from Kodak’s and Ilford’s datasheets, filters on digital and phone photos, and the filters in Clack.

01 · The rule

What a color filter does in black and white

Black and white film records how much light reaches it, not its color. A colored filter changes how much of each color gets there. It passes its own color and stops the rest, the opposite color most: Wikipedia’s rule of thumb is that a colored filter “will selectively lighten its color, while darkening other colors, especially the complementary color”. So a red filter passes red and stops cyan and blue; a yellow filter passes red and green and stops blue; a green filter stops red and magenta.

RedYellowGreenCyanBlueMagenta

The colors

As the eye sees

No filter

Yellow, No. 8

Orange, No. 21

Red, No. 25

Green, No. 58

Six colors, then the gray each prints as through Clack’s model of Kodak Tri-X 400: first as bright as the eye finds them, then as the film sees them with no filter and behind each filter, the exposure made up for the factor. Each filter lightens its own color and darkens the opposite one: red takes cyan and blue to near black, green does the same to red and magenta. The engine’s output on grade 3 paper, before grain.

02 · Why

Why black and white film needs a filter

Modern black and white film is panchromatic, sensitive to every color, but not in the eye’s proportions. The eye finds green brightest and blue darkest; film like Tri-X sees blue more strongly than green. Weighed against daylight, Tri-X takes red, green and blue about 0.21, 0.37 and 0.42, where the eye’s brightness takes them 0.21, 0.72 and 0.07 (our arithmetic from Kodak’s spectral sensitivity). Ilford HP5 Plus is close: 0.19, 0.43 and 0.38. So with no filter a blue sky prints pale and its clouds fade into it, and greens print darker than they look.

The eye’s brightness

2172

Tri-X 400, no filter

213742

Yellow, No. 8

3460

Orange, No. 21

5643

Red, No. 25

Green, No. 58

The share of red, green and blue in the gray, in percent: first the eye’s sense of brightness (the Rec. 709 weights), then Kodak Tri-X 400 by its spectral sensitivity in daylight, bare and behind each filter, as Clack’s engine holds them (our arithmetic from Kodak’s curves). Each row sums to 100: the filter’s lost light is made up by the exposure.

A yellow filter takes the blue back down. Behind one, Tri-X’s blue share falls from 42 % to 6 %, about the eye’s 7 %, and in the wedge above its yellow and blue print almost exactly as bright as the eye sees them (our arithmetic). That is why yellow is the usual first filter for black and white. Orange and red go past the eye, into a sky darker than it looked.

03 · Which

Which filter for black and white: yellow, orange, red or green

Filter	Blue sky	Skin	Foliage	Use
Yellow, No. 8	A little darker; clouds stand out	A touch lighter	A touch lighter	Skies closest to how the eye sees them; the usual first filter
Yellow-green, No. 11	Darker	Light to dark gray	Lighter	Portraits on panchromatic film (Wikipedia: the standard portrait filter); not in Clack
Orange, No. 21	Darker, clouds strong	Lighter	About the same; bright greens darker	Landscapes and skies, with skin still natural
Red, No. 25	Dark, near black in deep blue	Pale; lips light	About the same; bright greens dark	Dramatic skies, stone and brick against sky
Green, No. 58	A little darker	A touch darker; lips and reds dark	Lighter	Foliage, to tell greens apart
Blue, No. 47	Lighter	Darker	Darker	Haze and mist kept (Wikipedia: it accentuates haze); not in Clack

The sky, skin and foliage columns are what Clack’s model of Tri-X 400 prints behind each filter, against no filter (the wedge above, and a ColorChecker on the Tri-X 400 page). The yellow-green and blue rows, which Clack does not model, are from Wikipedia’s Photographic filter.

Yellow for any outdoor black and white: skies as you saw them, little light lost.
Orange when the sky matters: darker than yellow, and skin lighter than with no filter.
Red for drama: a dark sky behind white clouds, buildings or snow. Faces go pale and lips light, so it is rarely a portrait filter.
Green for foliage and gardens: greens lighter, and told apart (Wikipedia: “used to differentiate green tones”); reds darker.
Haze. Wikipedia names the yellow filter for cutting atmospheric haze, and the blue one for keeping it: a blue filter “tends to accentuate haze and lighten skies”.

04 · Factors

Filter factors for black and white film

A filter stops light, so the film needs more exposure behind it. The filter factor is how many times more: 2 is one stop, 4 two stops, 8 three stops. It depends on the film’s color sensitivity, so the same filter has a different factor on another film, and on the light: lamplight is redder than daylight, so a red filter costs less under it.

Filter	Tri-X 400, daylight (Kodak)	HP5 Plus, daylight (Ilford)	HP5 Plus, tungsten (Ilford)
Yellow, No. 8	2 (1 stop)	1.5 (⅔ stop)	1.2 (⅓ stop)
Yellow-green, No. 11	4 (2 stops)	Not listed	Not listed
Orange, No. 21	Not listed	2.3 (1⅓ stops)	2 (1 stop)
Red, No. 25	8 (3 stops)	8 (3 stops)	4 (2 stops)
Green, No. 58	6 (2⅔ stops)	6 (2⅔ stops)	6 (2⅔ stops)
Blue, No. 47	6 (2⅔ stops)	Not listed	Not listed
Polarizer	2.5 (1⅓ stops)	Not listed	Not listed

Kodak’s F-4017 and Ilford’s 1998 HP5 Plus sheet; the stops in brackets are our arithmetic, rounded to a third. Worked out from Kodak’s filter curves and each film’s sensitivity, Clack’s models land near the datasheets for red (7.1 on Tri-X, 8.0 on HP5 Plus) and above them for yellow (2.25 and 2.1) and green (9.5 and 7.8) (our arithmetic).

05 · How

How to use a color filter on black and white film

Pick the filter for the subject. Yellow for skies as the eye sees them, orange or red to darken them, green for foliage, yellow-green or none for faces. One filter at a time.
Find its factor for your film. The film’s datasheet lists it, as in the table above. A factor of 2 is one stop more exposure, 4 two stops, 8 three.
Meter, then open up by the factor. With a hand-held meter or the sunny 16 rule, meter without the filter and give the extra stops: a slower shutter or a wider aperture. A camera that meters through the lens makes up most of it itself.
Use the factor for the light. Lamplight is redder than daylight, so a red filter costs less under it. Ilford’s red No. 25 on HP5 Plus is 8 in daylight and 4 in tungsten.

The arithmetic for metering without a meter is in the sunny 16 calculator.

06 · Digital

Black and white filters on digital and phone photos

A digital camera or a phone records color, so the filter can come afterwards. Turning a color photo black and white is choosing how much red, green and blue make the gray, the same choice a filter makes on film. A red filter is close to the red channel alone: behind one, Tri-X takes red, green and blue 0.93, 0.06 and 0.02 (the bars above). Editors that let you weight each color in the black and white conversion can come close to any filter in the table, and change it later. Our black and white converter does it in the browser with the films’ own mixes: a photo on Street 400 or Press 400 behind each of the four filters.

A one-tap black and white filter in an app does the conversion with a mix the app chose, the same for every photo. A JPEG saved in black and white, by a camera’s monochrome mode or an app, has lost its color: it cannot be filtered again. Keep the color original if you may want a different sky later.

07 · Clack

Black and white filters in Clack

Clack is a film camera app for Android. Two of its eight films are black and white: Press 400 (based on Ilford HP5 Plus 400) and Street 400 (based on Kodak Tri-X 400). On both, Filter is one of the two dials under the finder, beside Contrast, and a control in the recipe editor: None, Yellow, Orange, Red, Green (Wratten 8, 21, 25 and 58).

From the data. Each filter is Kodak’s published WRATTEN 2 curve through the film’s own color sensitivity in daylight, so a red filter on Press 400 is not quite the same as on Street 400, as on film.
The exposure kept. Clack makes up the factor as a meter behind the lens would, so a filter changes which colors go light or dark, not how bright the frame is.
In the finder. The filter shows as you frame and is baked into the JPEG.

The film base: On Android phones whose camera offers a contrast curve, Clack takes the frame flat, with the phone’s local tone mapping and color enhancement off, before the film. On other phones the films run on the phone’s own frame.
Not in Clack: Yellow-green No. 11 and blue No. 47. Kodak’s WRATTEN 2 data has no curve for the No. 11.
Free or Pro: For seven days of shooting every film is open. After that the free tier keeps one film of your choice, which can be a black and white one, with its dials; Clack Pro has them all.

A model of the films’ data on a phone’s photo, not film. Tested mostly on the CMF Phone 2 Pro.

AndroidGet free access to the closed beta. More about Clack

Questions

What does a red filter do in black and white photography?: A red filter passes red and stops most blue and green. On black and white film a blue sky goes dark, near black in a deep blue, and clouds stay white; skin, lips and red things go light, and bright greens dark. It costs about three stops: Kodak and Ilford both give a daylight factor of 8 for their fast films.
What does a yellow filter do in black and white photography?: It holds back blue, so a blue sky prints a little darker and clouds stand out, about as the eye sees the scene. Panchromatic film sees blue more strongly than the eye, so with no filter skies print pale; behind a yellow filter Clack’s model of Tri-X prints blue almost exactly as dark as the eye finds it. Its factor is 1.5 to 2, one stop or less.
Which filter is best for black and white portraits?: Wikipedia calls a light yellow-green filter the standard portrait filter for panchromatic film. A yellow or orange filter lightens skin a little, orange more; a red filter lightens skin and lips a lot, which can look pale; a green filter darkens skin and lips.
Do you need color filters for black and white digital photos?: No. A digital camera records color, so the filter can be applied afterwards, in the black and white conversion: weight red up and blue down for a red filter’s sky. A JPEG saved in black and white has lost its color and cannot be filtered again.
What is a filter factor?: How many times more exposure a filter needs: 2 is one stop, 4 two stops, 8 three stops. It depends on the film’s color sensitivity and on the light, so datasheets list it per film, and sometimes for daylight and tungsten apart.
Can you use black and white filters on color film?: Not for the same purpose: a strong yellow, red or green filter tints the whole color picture. Color film uses light-balancing filters instead, such as the 81A to warm and the 82A to cool.
Is a polarizer a black and white filter?: It works on any film. A polarizer is colorless; it darkens blue sky most at about 90° from the sun and cuts reflections. Kodak gives it a factor of 2.5 on Tri-X. On black and white film a red or orange filter darkens a sky more.
What filters does Clack have for black and white?: Yellow, orange, red and green (Wratten 8, 21, 25 and 58), on its two black and white films, Press 400 and Street 400. Each is Kodak’s published filter curve through the film’s own color sensitivity, and the exposure is kept, as a meter behind the lens would.

Sources

Kodak, Tri-X and Wratten are Kodak’s or Kodak Alaris’s; Ilford and HP5 are HARMAN technology’s. Clack is not affiliated with either.