python jpeg文件24到32位转换

Question

我正在生成图像直方图，将 jpeg 文件读取到 24 位数组中，并将其转换为 32 位 numpy 以使用 numpy.histogram 进行处理，遵循以下方法：

• 将文件读入 numpy 数组形状：(w,h,3) -> img=imread(file,'RGB')
• 转换为字节块大小：w*h*3 -> by=img.tobytes()
• 使用结构迭代器解压 -> struct.iter_unpack('<3B',by)
• 转换为 int -> int.from_bytes(c, byteorder='big')

这种方法和我尝试过的其他方法（重塑为 w*h、3 等）的问题是 迭代器延迟，我的问题是：

有没有直接的方法在python中做到这一点没有迭代器，或者我应该写一个简单的C函数来做到这一点？

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

其他较慢的实现：

 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')])

编辑1：

找到了一个解决方案，创建一个 (w,h,4) numpy 数组并复制读取的图像，rest 简单快速（x40 从最快的迭代解决方案改进）

 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')

Answer 1

解决方案：

    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')