Desaturation

Desaturation is a quick way to create black and white images. Desaturation uses the midpoint between the high and low RGB values as the gray value. It results in a black and white conversion with less contrast than other methods.

Understanding the Hue/Saturation Layer

Desaturtion uses the Hue/Saturation layer.

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ScreenHunter_30 Apr. 17 12.58

Instead of the three RGB channels of red, green and blue, Hue/Saturation works on the hue, saturation and brightness (HSB) color notation:

Hue is the actual color. Instead of the color being a combination of red, green and blue channels, hue combines it into a single channel. The hue value ranges from 0° to 360°, with 0 being red, 120° being green and 240° being blue.

Saturation is the amount of color. Saturation is a value from 0% to 100%, with 100% being fully saturated and 0% being middle gray (128, 128, 128).

Brightness or Lightness is the amount of black or white. Brightness ranges from value 0 (complete black) to 100 (complete white).

Steps in Photoshop

Desaturation is setting the saturation level of all pixels to 0. This is what desaturation does to the color chart.

  1. Open the color chart in Photoshop.
  2. Add a Hue/Saturation… layer.
  3. Set saturation to 0.

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Desaturation
Desaturation

How Desaturation Works

Although desaturation uses the HSB color notation, Photoshop actually uses a simple conversion formula to get the equivalent gray value in RGB:

gray value = (MAX(r, g, b) + min(r, g, b))/2

For each pixel, the gray value is calculated by taking the average between the maximum RGB value and the minimum RGB value.

Example

Color:

Channel
Color Red Green Blue
120 225 162

Calculated Gray Value:

gray value = (MAX(r, g, b) + min(r, g, b))/2

MAX(r, g, b) = MAX(120, 225, 162) = 225
min(r, g, b) = min(120, 225, 162) = 120
(225 + 120)/2 = 345/2 = 172.5 ≈ 172

Channel
Color Red Green Blue
172 172 172

Going back to the color chart, it’s easy to see why all the colors result in the same shade of gray.

ColorChart

The maximum value for all colors is 255, and the minimum value is 0. The average between high and low for all colors is 128. Therefore all colors get converted to (128, 128, 128).

ColorChartDSat

Since desaturation takes the average between the high and low values, the colors get crushed towards a middle value. In real world examples, desaturation may result in a black and white image with less contrast.

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Parliament Hill – Example

There may be times when you want to apply different conversion methods to different parts of the image. Here’s how.

UPDATE: This tutorial uses some obsolete methods such as the hue/saturation method. I created this example about ten years ago, before Photoshop CS3 introduced black and white filters. If I were to redo this today I would use different conversion methods. However this tutorial, along with Selective Color, is a good example of how to use color selection during black and white processing. – DK
Continue reading Parliament Hill – Example

Genbaku Dome

Genbaku Dome, Hiroshima Japan
Genbaku Dome
Hiroshima Japan
Click to enlarge

Genbaku Dome, Hiroshima Japan

The Genbaku Dome, or Hiroshima Peace Memorial is part of the Hiroshima Peace Memorial Park. I took this photo on my trip to Japan in 2012. Hiroshima itself is a very ordinary city. However the history of the city and the museum made the visit a very moving experience.

Process

I processed this photo in Lightroom. Lightroom is currently my favorite way to process black and white. It adds a slight brown tint which gets rid of the blue tint that most digital b&w photos have.

For this photo I pushed the cyan and blue towards black to create a dark sky, and really boosted the contrast. I think it works for this subject.

Lab Color Mode

Lab color mode is a mode in Photoshop. Lab is different from RGB color mode in that it separates the luminosity information into it’s own channel. Lab mode has three channels: L, a and b.

The L Channel contains the image’s luminosity information. This allows you to manipulate the image’s luminosity without affecting it’s colors. The L channel is similar to black and white film in that it only records the image’s luminosity.
Continue reading Lab Color Mode

Grayscale Mode

Grayscale mode is a color mode in Photoshop. In grayscale mode, images are represented using only shades of gray rather than the full pallet of colors.

In RGB mode, the color of each pixel is stored as three numbers, or channels (nnn, nnn, nnn). If all three channels have the same value then the resulting color is a shade of gray.

Black (0,0,0)
Gray (80, 80, 80)
Gray (160, 160, 160)
White (255, 255, 255)

Continue reading Grayscale Mode

Selective Color

Hand-coloring has been used by photographers for over a century to add color to black and white photographs. This was done by hand painting the photograph with oil or watercolor paints. Unlike toning, which applies the same color to the entire image, selective coloring applies one or more colors to specific parts of the image.

The usual way to apply selective color is to use a mask and a solid color layer to apply color to specific parts of the image. However, by using Color Range selection and curves, you can create a more subtle look.

Selective Color

Continue reading Selective Color

RGB Color

RGB (Red, Green, Blue) is a way of describing color. Each color is described by a set of three numbers. For example, (102, 51, 255) describes THIS COLOR.

The color’s RGB value, written (n, n, n), describes the intensity of the red, green, and blue channels that make up that color. The range of values for each channel depends on the channel’s bit-depth, or how many bits are used for each channel.

Bit Depth Range
8 bit 0 – 255
16 bit 0 – 32768
32 bit 0.000 – 1.000

For example, in an 8-bit RGB each channel can have a value from 0 to 255. Zero means no brightness for that channel, 255 means maximum brightness. 8 bit RGB colors can range from (0, 0, 0) to (255, 255, 255) and every combination in between, or 2563 = 16,777,216 different colors.
Note that a 32 bit RGB should have an integer range between 0 and 232-1 or 4,294,967,295. However, this is normalized to a decimal value between 0.000 and 1.000.

Continue reading RGB Color