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# prix.py
"""
prix (Python Raster Image eXtensions)
A collection of routines useful for raster image processing,
mostly not associate with the PNG format, but
using datatypes from PyPNG.
"""
# https://pypi.org/project/pypng/
import png
def window(image, tl, br):
"""image is a png.Image instance (or like one).
A new png.Image instance is returned that
represents a windowed image.
The window is an axis aligned rectangle with opposite corners
at *tl* and *br* (each being an (x,y) pair).
As in ImageMagick (0,0) is the top-left.
Coordinates are usually integers, but can be passed as
`None` in which case the relevant image boundary will be
used (0 for left, image width for right, 0 for top, image
height for bottom).
"""
width, height = image.info["size"]
left, top = tl
right, bottom = br
if top is None:
top = 0
if left is None:
left = 0
if bottom is None:
bottom = height
if right is None:
right = width
if not (0 <= left < right <= width):
raise NotImplementedError()
if not (0 <= top < bottom <= height):
raise NotImplementedError()
# Compute left and right index bounds for each row,
# given that each row is a flat row of values.
l = left * image.info["planes"]
r = right * image.info["planes"]
def itercrop():
"""An iterator to perform the crop."""
for i, row in enumerate(image.rows):
if i < top:
continue
if i >= bottom:
# Same as "raise StopIteration"
return
yield row[l:r]
info = dict(image.info, size=(right - left, bottom - top))
return png.Image(itercrop(), info)
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