Pro Photo RGB Color Space

The ProPhoto RGB color space, also known as ROMM RGB (Reference Output Medium Metric), is an output referred RGB color space developed by Kodak. It offers an especially large gamut designed for use with photographic output in mind. The ProPhoto RGB color space encompasses over 90% of possible surface colors in the CIE L*a*b* color space, and 100% of likely occurring real world surface colors making ProPhoto even larger than the Wide Gamut RGB color space. The ProPhoto RGB primaries were also chosen in order to minimize hue rotations associated with non-linear tone scale operations. One of the downsides to this color space is that approximately 13% of the representable colors are imaginary colors that do not exist and are not visible colors. This means that potential color accuracy is wasted for reserving these unnecessary colors.

When working in color spaces with such a large gamut, it is recommended to work in 16-bit color depth to avoid posterization effects. This will occur more frequently in 8-bit modes as the gradient steps are much larger.

There are two corresponding scene space color encodings known as RIMM RGB intended to encode standard dynamic range scene space images, and ERIMM RGB intended to encode extended dynamic range scene space images.

ProPhoto RGB (ROMM RGB) Encoding Primaries

Color CIE x CIE y
red 0.7347 0.2653
green 0.1596 0.8404
blue 0.0366 0.0001
white 0.3457 0.3585

Viewing Environment

  • Luminance level is in the range of 160–640 cd/m2.
  • Viewing surround is average.
  • There is 0.5–1.0% viewing flare.
  • The adaptive white point is specified by the chromaticity values for CIE Standard Illuminant D50 (x = 0.3457, y = 0.3585).
  • The image color values are assumed to be encoded using flareless (or flare corrected) colorimetric measurements based on the CIE 1931 Standard Colorimetric Observer.

Encoding Function

X'_{ROMM} = \begin{cases} 0; & X_{ROMM} < 0.0 \\ 16X_{ROMM}I_{MAX}; & 0.0 \le X_{ROMM} < E_t \\ (X_{ROMM})^{1/1.8}I_{MAX}; & E_t \le X_{ROMM}<1.0 \\ I_{MAX}; & X_{ROMM} \ge 1.0 \end{cases}

where

and

is the maximum integer value used in the encoding function (e.g. 255 for 8-bit configuration)

and

Famous quotes containing the words pro, photo, color and/or space:

    “It is sweet and honourable to die for one’s country.
    [Dulce et decorum est pro patria mori.]”
    —Horace [Quintus Horatius Flaccus] (65–8 B.C.)

    “All photographs are there to remind us of what we forget. In this—as in other ways—they are the opposite of paintings. Paintings record what the painter remembers. Because each one of us forgets different things, a photo more than a painting may change its meaning according to who is looking at it.”
    —John Berger (b. 1926)

    “Painting seems to be to the eye what dancing is to the limbs. When that has educated the frame to self-possession, to nimbleness, to grace, the steps of the dancing-master are better forgotten; so painting teaches me the splendor of color and the expression of form, and as I see many pictures and higher genius in the art, I see the boundless opulence of the pencil, the indifferency in which the artist stands free to choose out of the possible forms.”
    —Ralph Waldo Emerson (1803–1882)

    “Thus all our dignity lies in thought. Through it we must raise ourselves, and not through space or time, which we cannot fill. Let us endeavor, then, to think well: this is the mainspring of morality.”
    —Blaise Pascal (1623–1662)