randphase

Python functions for generating phase-randomised images, with a focus on making visual controls for text.

• draw.text() creates images of text, cropped to the extremities of either the text or font.

• phase.randomise() randomises the phase of any image (including images of text). Fourier transform is used to extract amplitude. Inverse Fourier transform is used to generate an image with the same amplitude spectrum but with phase generated from uniformly distributed noise or a permutation of the original image's phase (which preserves the overall distribution of phase values).

Drawing Text

The draw.text() function can be used to create an image of text.

import draw
im = draw.text('example', size=50)
im.show()

This can be cropped to the extremities of the target text (as above), or to the maximum size available to the given number of ascii characters for the target font (for x and y separately).

crop1 = draw.text('brine', size=50, crop_x = 'font', crop_y='font')
crop2 = draw.text('bring', size=50, crop_x = 'font', crop_y='font')
crop3 = draw.text('WWWWW', size=50, crop_x = 'font', crop_y='font')
crop1.show()
crop2.show()
crop3.show()

You can also use different fonts, colours, backgrounds, and alignment (British spelling for 'centre' and 'colour').

text_spec = draw.text('fancy', font='BRUSHSCI.TTF', colour=(255,127,0), bg=(100,0,100),
                      border=(0,0,10,10), size=75, crop_x='font', align_x='centre')
text_spec.show()

Randomising Phase

Fourier transform is used to extract amplitude. Inverse Fourier transform is used to generate an image with the same amplitude spectrum but with phase generated from uniformly distributed noise or a permutation of the original image's phase (preserving the overall distribution of phase values).

To randomise the phase of an image with normally distributed noise, use phase.randomise(). This can be drawn from a uniform distribution (between $-\pi$ and $\pi$), or from a random permutation of the original phase values. Permuting the phase values can produce some very nice text-like noise patterns!

import phase
im = draw.text('erudition', size=50, font='courbd.ttf')
rp_im = phase.randomise(im, noise='uniform')
pp_im = phase.randomise(im, noise='permute')
im.show()
rp_im.show()
pp_im.show()

For text, this will occasionally lead to contrast artefacts, seen as black spots in the images above. This can be remedied with the contrast_adj argument, which proportionally alters the image's contrast before running the Fourier transform, and then reverts the result to the original image's contrast.

rp_im_adj = phase.randomise(text_im, noise='uniform', contrast_adj=0.5)
pp_im_adj = phase.randomise(text_im, noise='permute', contrast_adj=0.5)
im.show()
rp_im_adj.show()
pp_im_adj.show()

You can also control the proportion of the phase information which is noise.

u_010 = phase.randomise(im, noise='permute', noise_prop=0.1, contrast_adj=0.5)
u_025 = phase.randomise(im, noise='permute', noise_prop=0.25, contrast_adj=0.5)
u_050 = phase.randomise(im, noise='permute', noise_prop=0.50, contrast_adj=0.5)
u_075 = phase.randomise(im, noise='permute', noise_prop=0.75, contrast_adj=0.5)
u_100 = phase.randomise(im, noise='permute', noise_prop=1, contrast_adj=0.5)
im.show()
u_010.show()
u_025.show()
u_050.show()
u_075.show()
u_100.show()

This will work on text generated by draw.text(), or any other PIL image. If the image has RGBA channels, phase will be randomised across colour and alpha channels as well. Here is a summary of some example output from phase.randomise() (all with no contrast adjustment):

Dependencies

• PIL
• numpy