Module color

Color models

PostScript provides different color models. They are available to PyX by different color classes, which just pass the colors down to the PostScript level. This implies, that there are no conversion routines between different color models available. However, some color model conversion routines are included in Python’s standard library in the module colorsym. Furthermore also the comparison of colors within a color model is not supported, but might be added in future versions at least for checking color identity and for ordering gray colors.

There is a class for each of the supported color models, namely gray, rgb, cmyk, and hsb. The constructors take variables appropriate for the color model. Additionally, a list of named colors is given in appendix Appendix: Named colors.

Example

from pyx import *

c = canvas.canvas()

c.fill(path.rect(0, 0, 7, 3), [color.gray(0.8)])
c.fill(path.rect(1, 1, 1, 1), [color.rgb.red])
c.fill(path.rect(3, 1, 1, 1), [color.rgb.green])
c.fill(path.rect(5, 1, 1, 1), [color.rgb.blue])

c.writeEPSfile("color")

The file color.eps is created and looks like:

_images/color.png

Color example

Color gradients

The color module provides a class gradient for continous transitions between colors. A list of named gradients is available in appendix Appendix: Named gradients.

Note that all predefined non-gray gradients are defined in the RGB color space, except for gradient.Rainbow, gradient.ReverseRainbow, gradient.Hue, and gradient.ReverseHue, which are naturally defined in the HSB color space. Converted RGB and CMYK versions of these latter gradients are also defined under the names rgbgradient.Rainbow and cmykgradient.Rainbow, etc.

class color.gradient

This class defines the methods for the gradient.

getcolor(parameter)

Returns the color that corresponds to parameter (must be between min and max).

select(index, n_indices)

When a total number of n_indices different colors is needed from the gradient, this method returns the index-th color.

class color.functiongradient_cmyk(f_c, f_m, f_y, f_k)
class color.functiongradient_gray(f_gray)
class color.functiongradient_hsb(f_g, f_s, f_b)
class color.functiongradient_rgb(f_r, f_g, f_b)

This class provides an arbitray transition between colors of the same color model.

The functions f_c, etc. map the values [0, 1] to the respective components of the color model.

color.lineargradient_cmyk(mincolor, maxcolor)
color.lineargradient_gray(mincolor, maxcolor)
color.lineargradient_hsb(mincolor, maxcolor)
color.lineargradient_rgb(mincolor, maxcolor)

These factory functors for the corresponding functiongradient_ classes provide a linear transition between two given instances of the same color class. The linear interpolation is performed on the color components of the specific color model.

mincolor and maxcolor must be colors of the corresponding color class.

class rgbgradient(gradient)

This class takes an arbitrary gradient and converts it into one in the RGB color model. This is useful for instance in bitmap output, where only certain color models are supported in Postscript/PDF.

class cmykgradient(gradient)

This class takes an arbitrary gradient and converts it into one in the CMYK color mode. This is useful for instance in bitmap output, where only certain color models are supported in Postscript/PDF.

Transparency

class color.transparency(value)

Instances of this class will make drawing operations (stroking, filling) to become partially transparent. value defines the transparency factor in the range 0 (opaque) to 1 (transparent).

Transparency is available in PDF output only since it is not supported by PostScript. However, for certain ghostscript devices (for example the pdf backend as used by ps2pdf) proprietary PostScript extension allows for transparency in PostScript code too. PyX creates such PostScript proprietary code, but issues a warning when doing so.

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