一、将C++代码改为C#供今后参考:
static bool get_jpeg_size(byte[] data, int data_size, ref int width, ref int height)
{
//Check for valid JPEG image
int i = 0; // Keeps track of the position within the file
if (data[i] == 0xFF && data[i + 1] == 0xD8 && data[i + 2] == 0xFF && data[i + 3] == 0xE0)
{
i += 4;
// Check for valid JPEG header (null terminated JFIF)
if (data[i + 2] == J && data[i + 3] == F && data[i + 4] == I && data[i + 5] == F && data[i + 6] == 0x00)
{
//Retrieve the block length of the first block since the first block will not contain the size of file
var block_length = data[i] * 256 + data[i + 1];
while (i < data_size)
{
i += block_length; //Increase the file index to get to the next block
if (i >= data_size) return false; //Check to protect against segmentation faults
if (data[i] != 0xFF) return false; //Check that we are truly at the start of another block
if (data[i + 1] == 0xC0)
{ //0xFFC0 is the "Start of frame" marker which contains the file size
//The structure of the 0xFFC0 block is quite simple [0xFFC0][ushort length][uchar precision][ushort x][ushort y]
height = data[i + 5] * 256 + data[i + 6];
width = data[i + 7] * 256 + data[i + 8];
return true;
}
else
{
i += 2; //Skip the block marker
block_length = data[i] * 256 + data[i + 1]; //Go to the next block
}
}
return false; //If this point is reached then no size was found
}
else { return false; } //Not a valid JFIF string
}
else { return false; } //Not a valid SOI header
}
USAGE:
using (var stream = File.OpenRead(path))
{
using (var m = new MemoryStream())
{
stream.CopyTo(m);
var arr = m.ToArray();
int w = 0, h = 0;
get_jpeg_size(arr, arr.Length, ref w, ref h);
Console.WriteLine(w + "x" + h);
}
}
