Skip to main content

Why I love Python

I was reading "The remarkable inefficiency of word recognition" (Pelli et al. 2003) and I wanted to generate some of the stimuli they were using. In Python it took me a few hours total, starting cold using the Python Imaging Library. The code is below....
"""This contains routines to generate degraded letter stimuli"""

import Image #The PIL
import ImageDraw
import ImageFont

import numpy

def generate_letter(contrast_energy = .01, #michelson contrast energy
noise = 30.,
bg_luminance = 128.,
letter = "a",
letter_size = 400):
N = 300 #size of image in pixels

#first figure out what is the ink-area of the letter

font = ImageFont.truetype("Data/arial.ttf", letter_size)
#we copy the .ttf file to the local directory to avoid problems

im_temp ="1", (1,1), 0)
draw = ImageDraw.Draw(im_temp)
#now we can draw on this

sz = draw.textsize(letter, font=font)
#this tells us the size of the letter

im_temp ="1", sz, 0)
#this is a temporary binary image created solely for the purpose of computing
#the ink-area of the letter
draw = ImageDraw.Draw(im_temp)
#now we can draw on this
draw.text((0,0), letter, font=font, fill=1)
pix = im_temp.load()
#pix is now an addressable array of pixel values
area_in_pixels = 0.
for row in xrange(sz[0]):
for col in xrange(sz[1]):
area_in_pixels += pix[row,col]

#since contrast_energy = contrast^2 * pixel_area
contrast = (contrast_energy/area_in_pixels)**0.5
fg_luminance = bg_luminance*(1+contrast)/(1-contrast)
print area_in_pixels
print contrast
print fg_luminance

im ="L", (N,N), bg_luminance)
#im is now a NxN luminance image with luminance set to bg_luminance

draw = ImageDraw.Draw(im)
#now we can draw on this

draw.text(((N-sz[0])/2, (N-sz[1])/2), letter, font=font, fill=fg_luminance)
#this centers the letter

if noise > 0:
pix = im.load()
#pix is now an addressable array of pixel values

rd = numpy.random.normal(scale=noise, size=(N,N))
for row in xrange(N):
for col in xrange(N):
pix[row,col] += rd[row,col]


Popular posts from this blog

Flowing text in inkscape (Poster making)

You can flow text into arbitrary shapes in inkscape. (From a hint here).

You simply create a text box, type your text into it, create a frame with some drawing tool, select both the text box and the frame (click and shift) and then go to text->flow into frame.


The omnipresent anonymous asked:
Trying to enter sentence so that text forms the number three...any ideas?
The solution:
Type '3' using the text toolConvert to path using object->pathSize as necessaryRemove fillUngroupType in actual text in new text boxSelect the text and the '3' pathFlow the text

Pandas panel = collection of tables/data frames aligned by index and column

Pandas panel provides a nice way to collect related data frames together while maintaining correspondence between the index and column values:

import pandas as pd, pylab #Full dimensions of a slice of our panel index = ['1','2','3','4'] #major_index columns = ['a','b','c'] #minor_index df = pd.DataFrame(pylab.randn(4,3),columns=columns,index=index) #A full slice of the panel df2 = pd.DataFrame(pylab.randn(3,2),columns=['a','c'],index=['1','3','4']) #A partial slice df3 = pd.DataFrame(pylab.randn(2,2),columns=['a','b'],index=['2','4']) #Another partial slice df4 = pd.DataFrame(pylab.randn(2,2),columns=['d','e'],index=['5','6']) #Partial slice with a new column and index pn = pd.Panel({'A': df}) pn['B'] = df2 pn['C'] = df3 pn['D'] = df4 for key in pn.items: print pn[key] -> output …

Drawing circles using matplotlib

Use the pylab.Circle command

import pylab #Imports matplotlib and a host of other useful modules cir1 = pylab.Circle((0,0), radius=0.75, fc='y') #Creates a patch that looks like a circle (fc= face color) cir2 = pylab.Circle((.5,.5), radius=0.25, alpha =.2, fc='b') #Repeat (alpha=.2 means make it very translucent) ax = pylab.axes(aspect=1) #Creates empty axes (aspect=1 means scale things so that circles look like circles) ax.add_patch(cir1) #Grab the current axes, add the patch to it ax.add_patch(cir2) #Repeat