Hello,
I'm working on an image processing project using the Python Imaging
Library along with numpy. Right now, I'm trying to build a speedy
script for converting whole images between the RGB and the HSV (a.k.a.
HSB) color spaces. Unfortunately, the code I've made so far runs
dreadfully slow with even moderate-sized images.
I'm under the impression that the crux of the problem is the fact that
PIL's point method operates on only one band at a time, and to do a
proper color space conversion, you need information about all three
bands in a particular problem. This has forced me to do an awkward
work-around where the image data is loaded into a numpy array
(1600x1200x3), and a dinky for-loop run runs through the array picking
up RGB values, converting to HSV, and dumping the results back into
another array.
How can I make this more efficient?
--------
from PIL import Image
from PIL import TiffImagePlugin
from scipy.misc import pilutil
import numpy
import colorsys
def myrgbtohsv(r,g, b):
'''A wrapper for the colorsys function rgb_to_hsv
that takes r,g,b values between 0 and 255
(standard pixel value range in most of my single-band imaging
operations)
and returns the corresponding 255-scaled h,s,v values'''
tr = r/255.0
tg = g/255.0
tb = b/255.0
ur,ug,ub = colorsys.rgb_to _hsv(tr,tg,tb)
pr = int(round(ur,0) )*255
pg = int(round(ug,0) )*255
pb = int(round(ub,0) )*255
return pr,pg,pb
def rgbarrtohsvarr( pilarray):
'''Takes an 3d numpy ndarray loaded with a RGB PIL image and
converts
a copy of the contents to 255-scaled HSV array.
Returns the converted copy of the array.
'''
arrt = pilarray.copy()
r,c,d = arrt.shape
hsvarray = numpy.zeros((r, c,d))
print out
for i in range(0,r):
for j in range(0,c):
localrgb = (arrt[i,j,0],arrt[i,j,1],arrt[i,j,2])
(lh,ls,lv) = rgbtohsv(localr gb)
hsvarray[i,j,0],hsvarray[i,j,1],hsvarray[i,j,2]= lh,ls,lv
return hsvarray
im = Image.open(r'C: \test.tif')
arr = pilutil.fromima ge(im)
out = rgbarrtohsvarr( arr)
-------- 4 2215
ttest wrote:
Hello,
I'm working on an image processing project using the Python Imaging
Library along with numpy. Right now, I'm trying to build a speedy
script for converting whole images between the RGB and the HSV (a.k.a.
HSB) color spaces. Unfortunately, the code I've made so far runs
dreadfully slow with even moderate-sized images.
I'm under the impression that the crux of the problem is the fact that
PIL's point method operates on only one band at a time, and to do a
proper color space conversion, you need information about all three
bands in a particular problem. This has forced me to do an awkward
work-around where the image data is loaded into a numpy array
(1600x1200x3), and a dinky for-loop run runs through the array picking
up RGB values, converting to HSV, and dumping the results back into
another array.
How can I make this more efficient?
Reimplement colorsys.rgb_to _hsv() such that it operates on arrays instead of
scalars. Only minor modifications are necessary.
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
Reimplement colorsys.rgb_to _hsv() such that it operates on arrays instead of
scalars. Only minor modifications are necessary.
--
Robert Kern
Thanks! I'll try and see if a newcomer like me can get his head
around the array-centric modifications to colorsys.
ttest wrote:
>Reimplement colorsys.rgb_to _hsv() such that it operates on arrays instead of scalars. Only minor modifications are necessary.
-- Robert Kern
Thanks! I'll try and see if a newcomer like me can get his head
around the array-centric modifications to colorsys.
If you hit any roadblocks, drop in on numpy-discussion, and we'll help you out. http://www.scipy.org/Mailing_Lists
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
>
...where the image data is loaded into a numpy array
(1600x1200x3).. .
One comment: that is a big array, too big for the cache memory. I know
that in these cases it makes a difference how many times the slices of
the array are loaded and unloaded from RAM onto cache. One issue is
that a 2D array l[i,j] is actually a 1D array:
either
l[i,j]=l[i*N+j]
or
l[i,j]=l[j*N+i]
I don't know which in python/numpy. In the first case, when you fix i
and change j, you get consecutive positions in the underlying 1D
array, and they all belong to the same slice, which is loaded onto
cache very fast as a block. If you do the opposite, you are making
jumps to distant positions in the array (not a slice), and performance
suffers.
In gimp, for example, the underlying array is split into 'tiles',
which are 64x64 pixel regions that can be loaded/unloaded as a block.
And that's about all I know on the issue.
So it ma This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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