I have a captcha image that looks like this:
Using a utility called TesserCap from McAfee, I could app
Try something like this (pseudocode):
for each row of pixels:
if there is a group of about 3 or more pixels in a row, leave them
else remove the pixels
Then simply repeat the same thing for the columns. Seems like it might work at least a little. Going both horizontally and vertically like this will remove horizontal/vertical lines as well.
The algorithm essentially checks if there are multiple target pixels (in this case, non-white pixels) in a row, and changes those pixels if the number of pixels is less than or equal to the chop factor.
For example, in a sample row of pixels, where #
is black and -
is white, applying a chop factor of 2
would transform --#--###-##---#####---#-#
into ------###-------#####-------
. This is because there sequences of black pixels that are smaller than or equal to 2 pixels, and these sequences are replaced with white. The continuous sequences of greater than 2 pixels remain.
This is the result of the chop algorithm as implemented in my Python code (below) on the original image on your post:
In order to apply this to the whole image, you simply perform this algorithm on every row and on every column. Here's Python code that accomplishes that:
import PIL.Image
import sys
# python chop.py [chop-factor] [in-file] [out-file]
chop = int(sys.argv[1])
image = PIL.Image.open(sys.argv[2]).convert('1')
width, height = image.size
data = image.load()
# Iterate through the rows.
for y in range(height):
for x in range(width):
# Make sure we're on a dark pixel.
if data[x, y] > 128:
continue
# Keep a total of non-white contiguous pixels.
total = 0
# Check a sequence ranging from x to image.width.
for c in range(x, width):
# If the pixel is dark, add it to the total.
if data[c, y] < 128:
total += 1
# If the pixel is light, stop the sequence.
else:
break
# If the total is less than the chop, replace everything with white.
if total <= chop:
for c in range(total):
data[x + c, y] = 255
# Skip this sequence we just altered.
x += total
# Iterate through the columns.
for x in range(width):
for y in range(height):
# Make sure we're on a dark pixel.
if data[x, y] > 128:
continue
# Keep a total of non-white contiguous pixels.
total = 0
# Check a sequence ranging from y to image.height.
for c in range(y, height):
# If the pixel is dark, add it to the total.
if data[x, c] < 128:
total += 1
# If the pixel is light, stop the sequence.
else:
break
# If the total is less than the chop, replace everything with white.
if total <= chop:
for c in range(total):
data[x, y + c] = 255
# Skip this sequence we just altered.
y += total
image.save(sys.argv[3])