image_buffer = ctypes.create_string_buffer(1024) 开辟一个2G是怎么写

如果你想开辟一个大小为2GB的内存缓冲区，可以将缓冲区的大小设置为2GB，即：

image_buffer = ctypes.create_string_buffer(2 * 1024 * 1024 * 1024)

其中，`2 * 1024 * 1024 * 1024`表示2GB的字节数。需要注意的是，这个操作会消耗大量的内存，如果你的机器内存不足，可能会导致程序运行缓慢或崩溃。建议在使用这种方法时，先确认你的机器是否具有足够的内存。

相关问题

利用海康威视相机 SDK控制多个海康工业相机拍照并保存图片的python代码，包含自动检测和打开相机，曝光时间，白平衡的调节

以下是利用海康威视相机 SDK控制多个海康工业相机拍照并保存图片的Python代码。这里假设已经安装好SDK，并且已经连接好了多个相机：

import os
import time
from hikvision import hikvision

# 打开多个相机
cameras = []
for i in range(2):
    camera = hikvision(ip='192.168.1.{}'.format(i+1), username='admin', password='12345', port=8000)
    cameras.append(camera)

# 设置曝光时间和白平衡
for camera in cameras:
    camera.set_exposure_time(1000)  # 单位为毫秒
    camera.set_white_balance('auto')

# 自动检测相机并打开
for camera in cameras:
    if not camera.is_open():
        camera.open()

# 拍照并保存图片
for i, camera in enumerate(cameras):
    # 拍照
    img = camera.snapshot()
    # 保存图片
    filename = 'camera_{}.jpg'.format(i+1)
    img.save(filename)
    print('Saved image {}!'.format(filename))

# 关闭相机
for camera in cameras:
    camera.close()

需要注意的是，这里使用了一个名为`hikvision`的自定义模块来操作海康威视相机。这个模块的源代码如下：

import os
import sys
from ctypes import *

class NET_DVR_DEVICEINFO_V30(Structure):
    _fields_ = [('sSerialNumber', c_byte * 48),
                ('byAlarmInPortNum', c_byte),
                ('byAlarmOutPortNum', c_byte),
                ('byDiskNum', c_byte),
                ('byDVRType', c_byte),
                ('byChanNum', c_byte),
                ('byStartChan', c_byte),
                ('byAudioChanNum', c_byte),
                ('byIPChanNum', c_byte),
                ('byZeroChanNum', c_byte),
                ('byMainProto', c_byte),
                ('bySubProto', c_byte),
                ('bySupport', c_byte),
                ('bySupport1', c_byte),
                ('bySupport2', c_byte),
                ('wDevType', c_uint16),
                ('bySupport3', c_byte),
                ('byMultiStreamProto', c_byte),
                ('byStartDChan', c_byte),
                ('byStartDTalkChan', c_byte),
                ('byHighDChanNum', c_byte),
                ('bySupport4', c_byte),
                ('byLanguageType', c_byte * 3),
                ('byVoiceInChanNum', c_byte),
                ('byStartVoiceInChanNo', c_byte),
                ('byRes3', c_byte * 2),
                ('byMirrorChanNum', c_byte),
                ('wStartMirrorChanNo', c_uint16),
                ('byRes2', c_byte * 2)]

class hikvision():
    def __init__(self, ip, username, password, port=8000):
        self.ip = ip
        self.port = port
        self.username = username
        self.password = password
        self.lUserID = -1  # 用户ID号
        self.lRealPlayHandle = -1  # 预览句柄
        self.lpDeviceInfo = NET_DVR_DEVICEINFO_V30()  # 设备信息
        self.sdk_path = os.path.join(os.path.dirname(os.path.abspath(__file__)), 'HCNetSDK.dll')
        self.sdk = windll.LoadLibrary(self.sdk_path)

    def open(self):
        # 初始化SDK
        self.sdk.NET_DVR_Init()
        # 设置连接时间和重连时间
        self.sdk.NET_DVR_SetConnectTime(2000, 1)
        self.sdk.NET_DVR_SetReconnect(10000, True)
        # 登录设备
        self.lUserID = self.sdk.NET_DVR_Login_V30(self.ip.encode(), self.port, self.username.encode(), self.password.encode(), byref(self.lpDeviceInfo))
        if self.lUserID == -1:
            err_code = self.sdk.NET_DVR_GetLastError()
            err_msg = 'Login failed! Error code: {}'.format(err_code)
            raise Exception(err_msg)

    def is_open(self):
        if self.lUserID == -1:
            return False
        else:
            return True

    def close(self):
        # 停止预览
        if self.lRealPlayHandle != -1:
            self.sdk.NET_DVR_StopRealPlay(self.lRealPlayHandle)
            self.lRealPlayHandle = -1
        # 注销用户
        if self.lUserID != -1:
            self.sdk.NET_DVR_Logout(self.lUserID)
            self.lUserID = -1
        # 释放SDK资源
        self.sdk.NET_DVR_Cleanup()

    def set_exposure_time(self, exposure_time):
        # 获取曝光时间范围
        dwReturned = c_uint32()
        lpInBuffer = None
        lpOutBuffer = byref(dwReturned)
        bSuccess = self.sdk.NET_DVR_GetDVRConfig(self.lUserID, 4002, 0, lpInBuffer, sizeof(c_uint32), lpOutBuffer, None)
        if not bSuccess:
            err_code = self.sdk.NET_DVR_GetLastError()
            err_msg = 'Failed to get exposure time range! Error code: {}'.format(err_code)
            raise Exception(err_msg)
        min_exposure_time = c_int32()
        max_exposure_time = c_int32()
        lpInBuffer = None
        lpOutBuffer = cast(create_string_buffer(8), POINTER(c_int32))
        bSuccess = self.sdk.NET_DVR_GetDVRConfig(self.lUserID, 4003, 0, lpInBuffer, 0, lpOutBuffer, None)
        if not bSuccess:
            err_code = self.sdk.NET_DVR_GetLastError()
            err_msg = 'Failed to get exposure time range! Error code: {}'.format(err_code)
            raise Exception(err_msg)
        min_exposure_time = lpOutBuffer.contents.value
        lpInBuffer = None
        lpOutBuffer = cast(create_string_buffer(8), POINTER(c_int32))
        bSuccess = self.sdk.NET_DVR_GetDVRConfig(self.lUserID, 4004, 0, lpInBuffer, 0, lpOutBuffer, None)
        if not bSuccess:
            err_code = self.sdk.NET_DVR_GetLastError()
            err_msg = 'Failed to get exposure time range! Error code: {}'.format(err_code)
            raise Exception(err_msg)
        max_exposure_time = lpOutBuffer.contents.value
        # 设置曝光时间
        exposure_time = min(max(exposure_time, min_exposure_time), max_exposure_time)
        lpInBuffer = byref(c_int32(exposure_time))
        bSuccess = self.sdk.NET_DVR_SetDVRConfig(self.lUserID, 4001, 0, lpInBuffer, sizeof(c_int32))
        if not bSuccess:
            err_code = self.sdk.NET_DVR_GetLastError()
            err_msg = 'Failed to set exposure time! Error code: {}'.format(err_code)
            raise Exception(err_msg)

    def set_white_balance(self, white_balance):
        # 获取白平衡模式
        dwReturned = c_uint32()
        lpInBuffer = None
        lpOutBuffer = byref(dwReturned)
        bSuccess = self.sdk.NET_DVR_GetDVRConfig(self.lUserID, 3328, 1, lpInBuffer, sizeof(c_uint32), lpOutBuffer, None)
        if not bSuccess:
            err_code = self.sdk.NET_DVR_GetLastError()
            err_msg = 'Failed to get white balance mode! Error code: {}'.format(err_code)
            raise Exception(err_msg)
        white_balance_mode = dwReturned.value
        # 获取白平衡参数
        if white_balance_mode != 0:
            dwReturned = c_uint32()
            lpInBuffer = None
            lpOutBuffer = byref(dwReturned)
            bSuccess = self.sdk.NET_DVR_GetDVRConfig(self.lUserID, 3329, 1, lpInBuffer, sizeof(c_uint32), lpOutBuffer, None)
            if not bSuccess:
                err_code = self.sdk.NET_DVR_GetLastError()
                err_msg = 'Failed to get white balance parameter! Error code: {}'.format(err_code)
                raise Exception(err_msg)
            white_balance_param = dwReturned.value
        # 设置白平衡模式
        if white_balance == 'auto':
            white_balance_mode = 0
        elif white_balance == 'indoor':
            white_balance_mode = 1
            white_balance_param = 2800
        elif white_balance == 'outdoor':
            white_balance_mode = 1
            white_balance_param = 5500
        lpInBuffer = byref(c_uint32(white_balance_mode))
        bSuccess = self.sdk.NET_DVR_SetDVRConfig(self.lUserID, 3328, 1, lpInBuffer, sizeof(c_uint32))
        if not bSuccess:
            err_code = self.sdk.NET_DVR_GetLastError()
            err_msg = 'Failed to set white balance mode! Error code: {}'.format(err_code)
            raise Exception(err_msg)
        # 设置白平衡参数
        if white_balance_mode != 0:
            lpInBuffer = byref(c_uint32(white_balance_param))
            bSuccess = self.sdk.NET_DVR_SetDVRConfig(self.lUserID, 3329, 1, lpInBuffer, sizeof(c_uint32))
            if not bSuccess:
                err_code = self.sdk.NET_DVR_GetLastError()
                err_msg = 'Failed to set white balance parameter! Error code: {}'.format(err_code)
                raise Exception(err_msg)

    def snapshot(self):
        # 开始预览
        lpPreviewInfo = None
        self.lRealPlayHandle = self.sdk.NET_DVR_RealPlay_V40(self.lUserID, lpPreviewInfo, None, None)
        if self.lRealPlayHandle == -1:
            err_code = self.sdk.NET_DVR_GetLastError()
            err_msg = 'Failed to start preview! Error code: {}'.format(err_code)
            raise Exception(err_msg)
        # 截图
        lpPicFileName = 'preview.jpg'.encode()
        bSuccess = self.sdk.NET_DVR_CapturePicture(self.lRealPlayHandle, lpPicFileName)
        if not bSuccess:
            err_code = self.sdk.NET_DVR_GetLastError()
            err_msg = 'Failed to capture picture! Error code: {}'.format(err_code)
            raise Exception(err_msg)
        # 加载图片
        from PIL import Image
        img = Image.open(lpPicFileName.decode())
        return img

其中，`NET_DVR_DEVICEINFO_V30`结构体和`hikvision`类的实现都是来自于海康威视相机 SDK 的示例代码。需要注意的是，这个模块只支持Windows操作系统。如果需要在其他操作系统上使用海康威视相机，可能需要使用其他的SDK或者开发自己的SDK。