components.colourspace.gammacorrection

pyctools.components.colourspace.gammacorrection.GammaCorrect

Gamma correction.

pyctools.components.colourspace.gammacorrection.PiecewiseGammaCorrect

Gamma correction with a piecewise linear transform.

pyctools.components.colourspace.gammacorrection.apply_transfer_function

Apply a transfer function to a single 3-D numpy.ndarray.

class GammaCorrect(config={}, **kwds)[source]

Bases: pyctools.core.base.Transformer

Gamma correction.

Convert linear intensity values to ‘gamma corrected’ form suitable for display or storage in standard video or image files.

In inverse mode gamma corrected data is converted to linear intensity.

The 'hybrid_log' gamma option is an implementation of a proposal from BBC R&D for HDR imaging. See http://www.bbc.co.uk/rd/publications/whitepaper309 for more information.

The 'S-Log' option is taken from a Sony document https://pro.sony.com/bbsccms/assets/files/mkt/cinema/solutions/slog_manual.pdf

'Canon-Log' is taken from a white paper on the EOS C300 camera: http://learn.usa.canon.com/app/pdfs/white_papers/White_Paper_Clog_optoelectronic.pdf

The gamma options have all been normalised so that linear intensity black level input produces a gamma corrected output of 0 and linear intensity white level input produces an output of 255. The linear intensity black and white values are set by the black and white config items. You can use an Arithmetic or ComputerToStudio component to scale the output if required.

The scale option adjusts the input and output ranges without changing the mapping from input white to output 255. With some functions this acts as a highlight compression adjustment.

The function output emits the transfer function data whenever it changes. It can be connected to a PlotData component.

Config

black

float

“Linear intensity” black level.

white

float

“Linear intensity” white level.

scale

float

Adjust the range of some functions.

gamma

str

Choose a gamma curve. Possible values: 'linear', 'bt709', 'srgb', 'adobe_rgb', 'hybrid_log', 'S-Log', 'Canon-Log'.

knee

bool

Turn on “knee” (highlight compression).

knee_point

float

Highlight compression threshold (normalised 0..1 range).

knee_slope

float

Slope of transfer function above knee threshold.

inverse

bool

outputs = ['output', 'function']
class PiecewiseGammaCorrect(config={}, **kwds)[source]

Bases: pyctools.core.base.Transformer

Gamma correction with a piecewise linear transform.

The transform is specified as a series of input values and corresponding output values. Linear interpolation is used to convert data that lies between in_vals values, and extrapolation is used for data outside the range of in_vals.

The function output emits the transfer function data whenever it changes. It can be connected to the PlotData component.

The smooth option (present if scipy is installed) converts the series of data points to a smooth curve using cubic spline interpolation.

Config

in_vals

str

List of input values, in increasing order.

out_vals

str

List of corresponding output values.

inverse

bool

smooth

bool

Smooth transform with cubic spline interpolation. Requires scipy.

outputs = ['output', 'function']
apply_transfer_function()

Apply a transfer function to a single 3-D numpy.ndarray.

The function is defined by two 1-D arrays - input values in_val and the corresponding output values out_val. Linear interpolation is used to map input values that lie between members of the in_val list. Input values outside the range of in_val are mapped by extrapolation from the first or last two values.

Parameters

Comments or questions? Please email jim@jim-easterbrook.me.uk.