Photographic Tone Mapping Filter

Filter

RIF_IMAGE_FILTER_PHOTO_TONEMAP

Description

Photographic tone mapper that emulates the work of camera.

Based on following formulas:

https://en.wikipedia.org/wiki/Film_speed#Measurements_and_calculations

First we compute the luminous exposure H (in lux seconds):

../../_images/photographic_tone_mapper_f1.svg

where q is:

../../_images/photographic_tone_mapper_f2.svg

For the theta angle, we use a typical value of 10°, for T - 0.9, vignette v is an input parameter.

Then computation diverge based on weather or not a user wants to provide an input value for film ISO or wants to compute film sensitivity in kernel. If ISO is provided and user enables useISO define (see the Parameters section), we compute the final film sensitivity as ISO / 100 and use it in the final pixel value computation. Otherwise, we compute standard output sensitivity using the following formula:

../../_images/photographic_tone_mapper_f3.svg

where lx * s = H and Hsos is the exposure that will lead to values of @saturation in pixels.

Parameters

Parameter	Type	Input/Output	Description
gamma	float	input	Gamma correction value. Value range is [0, 5], default value is 1.
exposureTime	float	input	Film exposure time. Value range is [0, 100], default value is 0.125.
sensitivity	float	input	Luminance of the scene (in candela per m^2). Value range is [0, 100], default value is 1.
fstop	float	input	Aperture f-number. Value range is [0.00001, 100], default value is 1.
focalL	float	input	Camera focal length. Value range is [0.1, 10], default value is 1.
vignette	float	input	Vignette value. Value range is [0, 1], default value is 0.
saturation	float	input	Saturation used for sensitivity computation. Value range is [0, 1], default value is 0.5.
lighten	float	input	Brighten up highlights. Higher settings bring highlights closer to white. Value range is [0, 10], default value is 0.5.
darken	float	input	Darken shadowed areas. Higher settings bring shadowed areas closer to black. Value range is [0, 10], default value is 0.5.
ISO	uint	input	Film ISO value. Value range is [100, 2000], default value is 100.
useclampN	uint	input	If set to `RIF_TRUE`, negative values are clamped to zero. Values are `RIF_FALSE` and `RIF_TRUE` (default).
whitepoint	float4	input	The color that will be mapped to white in the output. Default value is (1, 1, 1, 1).
useISO	uint	input	If set to `RIF_FALSE`, use saturation to compute sensitivity. Otherwise, use the provided ISO. Values are `RIF_FALSE` (default) and `RIF_TRUE`.