Re: Reverse order of bit in repeating seqence of byte string
imageguy wrote:
On Jan 2, 7:33 pm, John Machin wrote:
For some very strange definition of "works"
Well that's embarrassing ... you are correct. I need to convert from
'bgr' to 'rgb'
If that is the only issue:
>>> import Image
>>> p = Image.open('~/VPython.png')
>>> r, g, b = p.split()
>>> q = Image.merge('RGB', [b, r, g])
>>> q.save('~/VPython1.png')
Should be plenty fast.
Read the PIL docs before rolling your own solutions.
--Scott David Daniels
scott.dani...@acm.org
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Re: Reverse order of bit in repeating seqence of byte string
On Jan 4, 7:10 am, imageguy wrote: > On Jan 2, 7:33 pm, John Machin wrote: > > > For some very strange definition of "works". You say you have 'bgr' > > and want to convert it to 'rbg'. The following code converts 'bgr' to > > 'rgb', which is somewhat more plausible, but not what you said you > > wanted. > > Well that's embarrassing ... you are correct. I need to convert from > 'bgr' to 'rgb' > > Thanks to all others for suggestions > > FWIW, I realized the the C.types string buffer is/was mutable so > settled on this; > > for start in xrange(0, ctypes.sizeof(buffer), 3): > if buffer[start] != buffer[start+2]: > #only need to swap the bits if they are different. ie if > both are white or black, no change is required. > blue, red = buffer[start], buffer[start+2] > buffer[start], buffer[start+2] = red, blue You are likely find that using buffer[start], buffer[start+2] = buffer[start+2], buffer[start] is faster. Cheers, John -- http://mail.python.org/mailman/listinfo/python-list
Re: Reverse order of bit in repeating seqence of byte string
On Jan 2, 7:33 pm, John Machin wrote: > For some very strange definition of "works". You say you have 'bgr' > and want to convert it to 'rbg'. The following code converts 'bgr' to > 'rgb', which is somewhat more plausible, but not what you said you > wanted. Well that's embarrassing ... you are correct. I need to convert from 'bgr' to 'rgb' Thanks to all others for suggestions FWIW, I realized the the C.types string buffer is/was mutable so settled on this; for start in xrange(0, ctypes.sizeof(buffer), 3): if buffer[start] != buffer[start+2]: #only need to swap the bits if they are different. ie if both are white or black, no change is required. blue, red = buffer[start], buffer[start+2] buffer[start], buffer[start+2] = red, blue This was about 30-40% faster that converting to list, processing and then converting back again. Will try the array module too ... but I think I need to find a new graphic package rather that makes working with the bits easier. g. -- http://mail.python.org/mailman/listinfo/python-list
Re: Reverse order of bit in repeating seqence of byte string
imageguy wrote: > I am looking for the most efficient method of replacing a repeating > sequence in a byte string returned from a imaging .dll, connected via > > I receive the byte string with the following sequence 'bgrbgrbgrbgr' > and I would like to convert this to 'rbgrbgrbgrbg' > FWIW, the string is created using ctypes.create_string_buffer function > > The following code works but feels a bit clunk and is rather slow too. > > blist = list(buffer) > for start in xrange(0,len(blist), 3): >try: > blue = blist[start] > red = blist[start+2] > blist[start] = red > blist[start+2] = blue >except IndexError: >pass > > new_buffer = ''.join(blist) > > new_buffer is then passed to a wx program to create and image. > > Any thoughts comments would be appreciated. > > geoff. > > PS: I started this post earlier, but I think I hit the send button > too soon. My apologies to the group for sloppy typing. > > -- > http://mail.python.org/mailman/listinfo/python-list > I've not seen anyone mention numpy yet, but numpy has a nice (efficient) way to do this: >>> import numpy >>> s = 'bgrBGRcbaCBA' >>> a=numpy.array(s, 'c') # Initialize an array >>> a.shape = (4,3)# Reinterpret as a ?? by 3 array >>> b=a[...,::-1] # reverse the second dimension >>> print b.tostring() # Convert back to a string. rgbRGBabcABC Gary Herron -- http://mail.python.org/mailman/listinfo/python-list
Re: Reverse order of bit in repeating seqence of byte string
On Jan 3, 5:34 am, imageguy wrote: > I am looking for the most efficient method of replacing a repeating > sequence in a byte string returned from a imaging .dll, connected via > > I receive the byte string with the following sequence 'bgrbgrbgrbgr' > and I would like to convert this to 'rbgrbgrbgrbg' > FWIW, the string is created using ctypes.create_string_buffer function > > The following code works but feels a bit clunk and is rather slow too. For some very strange definition of "works". You say you have 'bgr' and want to convert it to 'rbg'. The following code converts 'bgr' to 'rgb', which is somewhat more plausible, but not what you said you wanted. > > blist = list(buffer) > for start in xrange(0,len(blist), 3): > try: > blue = blist[start] > red = blist[start+2] > blist[start] = red > blist[start+2] = blue > except IndexError: > pass > > new_buffer = ''.join(blist) > -- http://mail.python.org/mailman/listinfo/python-list
Re: Reverse order of bit in repeating seqence of byte string
imageguy:
> I receive the byte string with the following sequence 'bgrbgrbgrbgr'
> and I would like to convert this to 'rbgrbgrbgrbg'
> FWIW, the string is created using ctypes.create_string_buffer function
MRAB:
> >>> a.tostring()
> '210543876'
That's not the required 'rbgrbgrbgrbg', but you are close to a correct
solution:
>>> from array import array
>>> s = 'bgrbgrbgrbgr'
>>> a = array("B", s) # uppercase B
>>> a[0::3], a[1::3], a[2::3] = a[2::3], a[0::3], a[1::3]
>>> a.tostring()
'rbgrbgrbgrbg'
Bye,
bearophile
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Re: Reverse order of bit in repeating seqence of byte string
Francesco Bochicchio wrote:
imageguy ha scritto:
I am looking for the most efficient method of replacing a repeating
sequence in a byte string returned from a imaging .dll, connected via
I receive the byte string with the following sequence 'bgrbgrbgrbgr'
and I would like to convert this to 'rbgrbgrbgrbg'
FWIW, the string is created using ctypes.create_string_buffer function
The following code works but feels a bit clunk and is rather slow too.
blist = list(buffer)
for start in xrange(0,len(blist), 3):
try:
blue = blist[start]
red = blist[start+2]
blist[start] = red
blist[start+2] = blue
except IndexError:
pass
new_buffer = ''.join(blist)
new_buffer is then passed to a wx program to create and image.
Any thoughts comments would be appreciated.
geoff.
PS: I started this post earlier, but I think I hit the send button
too soon. My apologies to the group for sloppy typing.
You could try the same algorithm on an array.array object : it might be
faster.
>>> s = "012345678"
>>> from array import array
>>> a = array("b", s)
>>> a
array('b', [48, 49, 50, 51, 52, 53, 54, 55, 56])
>>> a[0::3], a[2::3] = a[2::3], a[0::3]
>>> a
array('b', [50, 49, 48, 53, 52, 51, 56, 55, 54])
>>> a.tostring()
'210543876'
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Re: Reverse order of bit in repeating seqence of byte string
imageguy wrote: I am looking for the most efficient method of replacing a repeating sequence in a byte string returned from a imaging .dll, connected via I receive the byte string with the following sequence 'bgrbgrbgrbgr' and I would like to convert this to 'rbgrbgrbgrbg' For speed, I would look at PIL or pygame for existing function, or use numpy -- read into 2-d array, swap first and third members, flatten. -- http://mail.python.org/mailman/listinfo/python-list
Re: Reverse order of bit in repeating seqence of byte string
imageguy ha scritto: I am looking for the most efficient method of replacing a repeating sequence in a byte string returned from a imaging .dll, connected via I receive the byte string with the following sequence 'bgrbgrbgrbgr' and I would like to convert this to 'rbgrbgrbgrbg' FWIW, the string is created using ctypes.create_string_buffer function The following code works but feels a bit clunk and is rather slow too. blist = list(buffer) for start in xrange(0,len(blist), 3): try: blue = blist[start] red = blist[start+2] blist[start] = red blist[start+2] = blue except IndexError: pass new_buffer = ''.join(blist) new_buffer is then passed to a wx program to create and image. Any thoughts comments would be appreciated. geoff. PS: I started this post earlier, but I think I hit the send button too soon. My apologies to the group for sloppy typing. You could try the same algorithm on an array.array object : it might be faster. Ciao FB -- http://mail.python.org/mailman/listinfo/python-list
Re: Reverse order of bit in repeating seqence of byte string
imageguy wrote:
> I am looking for the most efficient method of replacing a repeating
> sequence in a byte string returned from a imaging .dll, connected via
>
> I receive the byte string with the following sequence 'bgrbgrbgrbgr'
> and I would like to convert this to 'rbgrbgrbgrbg'
> FWIW, the string is created using ctypes.create_string_buffer function
>
> The following code works but feels a bit clunk and is rather slow too.
>
> blist = list(buffer)
> for start in xrange(0,len(blist), 3):
>try:
> blue = blist[start]
> red = blist[start+2]
> blist[start] = red
> blist[start+2] = blue
>except IndexError:
>pass
>
> new_buffer = ''.join(blist)
>
> new_buffer is then passed to a wx program to create and image.
>
> Any thoughts comments would be appreciated.
>
> geoff.
>
> PS: I started this post earlier, but I think I hit the send button
> too soon. My apologies to the group for sloppy typing.
>
May not be any quicker, but it works:
blues = buffer[0::3]
greens = buffer[1::3]
reds = buffer[2::3]
result = "".join("".join(x) for x in zip(reds, blues, greens))
regards
Steve
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Reverse order of bit in repeating seqence of byte string
I am looking for the most efficient method of replacing a repeating sequence in a byte string returned from a imaging .dll, connected via I receive the byte string with the following sequence 'bgrbgrbgrbgr' and I would like to convert this to 'rbgrbgrbgrbg' FWIW, the string is created using ctypes.create_string_buffer function The following code works but feels a bit clunk and is rather slow too. blist = list(buffer) for start in xrange(0,len(blist), 3): try: blue = blist[start] red = blist[start+2] blist[start] = red blist[start+2] = blue except IndexError: pass new_buffer = ''.join(blist) new_buffer is then passed to a wx program to create and image. Any thoughts comments would be appreciated. geoff. PS: I started this post earlier, but I think I hit the send button too soon. My apologies to the group for sloppy typing. -- http://mail.python.org/mailman/listinfo/python-list
