CODEWITHSUNDEEP
pythonjpegbit
roberto
roberto

Reputation: 577

python jpeg file 24 to 32 bit conversion

i'm generating image histograms reading jpeg files into a 24 bit array and the converting it to a 32 bit numpy one for processing with numpy.histogram, following this approach:

the problem with this approach and others i've tried (reshaping to w*h,3, etc.)is the iterator delay, my question is:

is there a direct way to do this in python without iterators, or should i write a simple C function to do it?

 def jpeg2colors(fnme):
    return np.asarray(
        [int.from_bytes(c, byteorder='big')
         for c in struct.iter_unpack('<3B', imread(fnme).tobytes())])

the other slower implementations:

 def conversionSLOW(fnme):  # reshape to (w*h,3)
    img = imread(fnme, mode='RGB')
    return np.array([int.from_bytes(c, byteorder='big')
                     for c in img.reshape((img.shape[0] * img.shape[1], 3))])

def conversionbyte01(fnme): # int iteration -> closer to fastests
    by = imread(fnme, mode='RGB').tobytes()
    return np.asanyarray([int.from_bytes(by[c:c + 3], byteorder='big')
                          for c in range(0, len(by) - 3, 3)],
                         dtype=np.int32)

def conversionbyte02(fnme):
    img = imread(fnme)
    return np.array([int.from_bytes(c, byteorder='big') for c in img.reshape(img.shape[0] * img.shape[1], 3)])

def conversionbyte03(fnme):
    img = imread(fnme)
    return np.array([int.from_bytes(img.reshape(img.shape[0] * img.shape[1], 3), byteorder='big')])

EDIT1:

found a solution creating a (w,h,4) numpy array and copying read image, rest is simple and fast (x40 improvement from fastest iteration solution)

 def fromJPG2_2int32_stbyst(fnme): # step by step
    img = imread(fnme)
    # create a (w,h,4) array and copy original
    re = np.zeros((img.shape[0], img.shape[1], 4), dtype=np.uint8) 
    re[:, :, :-1] = img
    # lineup to a byte structure ready for ' frombuffer'
    re1 = re.reshape(img.shape[0] * img.shape[1] * 4)
    by = re1.tobytes()
    # got it just convert to int
    cols = np.frombuffer(by, 'I')
    return cols

def fromJPG2_2int32_v0(fnme): # more compact & efficient
    img = imread(fnme)
    re = np.zeros((img.shape[0], img.shape[1], 4), dtype=np.uint8)
    re[:, :, :-1] = img
    return np.frombuffer(re.reshape(img.shape[0] * img.shape[1] * 4).tobytes(), 'I')

def fromJPG2_2int32(fnme): # even better using numpy.c_[]
    img = imread(fnme)
    img = np.c_[img, np.zeros((img.shape[0], img.shape[1], 1), dtype=np.uint8)]
    return np.frombuffer(img.reshape(img.shape[0] * img.shape[1] * 4).tobytes(), 'I')

Upvotes: 0

Views: 665

Answers (1)

roberto
roberto

Reputation: 577

solution:

    def fromjpg2int32(fnme):  # convert jpg 2 int color array
    img = imread(fnme)
    return np.frombuffer(
        np.insert(img, 3, values=0, axis=2).
            reshape(img.shape[0] * img.shape[1] * 4).tobytes(), 'I')

Upvotes: 1

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