43

我需要访问位图的每个像素,使用它们,然后将它们保存到位图。

使用Bitmap.GetPixel()and Bitmap.SetPixel(),我的程序运行缓慢。

如何快速转换Bitmapbyte[]返回?

我需要一个byte[]with length = (4 * width * height),包含每个像素的 RGBA 数据。

4

7 回答 7

90

你可以通过几种不同的方式来做到这一点。您可以使用unsafe来直接访问数据,也可以使用编组来来回复制数据。不安全代码更快,但编组不需要不安全代码。这是我不久前做的性能比较

以下是使用 lockbits 的完整示例:

/*Note unsafe keyword*/
public unsafe Image ThresholdUA(float thresh)
{
    Bitmap b = new Bitmap(_image);//note this has several overloads, including a path to an image

    BitmapData bData = b.LockBits(new Rectangle(0, 0, _image.Width, _image.Height), ImageLockMode.ReadWrite, b.PixelFormat);

    byte bitsPerPixel = GetBitsPerPixel(bData.PixelFormat);

    /*This time we convert the IntPtr to a ptr*/
    byte* scan0 = (byte*)bData.Scan0.ToPointer();

    for (int i = 0; i < bData.Height; ++i)
    {
        for (int j = 0; j < bData.Width; ++j)
        {
            byte* data = scan0 + i * bData.Stride + j * bitsPerPixel / 8;

            //data is a pointer to the first byte of the 3-byte color data
            //data[0] = blueComponent;
            //data[1] = greenComponent;
            //data[2] = redComponent;
        }
    }

    b.UnlockBits(bData);

    return b;
}

这是同样的事情,但有编组:

/*No unsafe keyword!*/
public Image ThresholdMA(float thresh)
{
    Bitmap b = new Bitmap(_image);

    BitmapData bData = b.LockBits(new Rectangle(0, 0, _image.Width, _image.Height), ImageLockMode.ReadWrite, b.PixelFormat);

    /* GetBitsPerPixel just does a switch on the PixelFormat and returns the number */
    byte bitsPerPixel = GetBitsPerPixel(bData.PixelFormat);

    /*the size of the image in bytes */
    int size = bData.Stride * bData.Height;

    /*Allocate buffer for image*/
    byte[] data = new byte[size];

    /*This overload copies data of /size/ into /data/ from location specified (/Scan0/)*/
    System.Runtime.InteropServices.Marshal.Copy(bData.Scan0, data, 0, size);

    for (int i = 0; i < size; i += bitsPerPixel / 8 )
    {
        double magnitude = 1/3d*(data[i] +data[i + 1] +data[i + 2]);

        //data[i] is the first of 3 bytes of color

    }

    /* This override copies the data back into the location specified */
    System.Runtime.InteropServices.Marshal.Copy(data, 0, bData.Scan0, data.Length);

    b.UnlockBits(bData);

    return b;
}
于 2009-10-13T21:59:37.927 回答
6

您可以使用 Bitmap.LockBits 方法。此外,如果您想使用并行任务执行,您可以使用 System.Threading.Tasks 命名空间中的 Parallel 类。以下链接有一些示例和解释。

于 2014-09-03T11:39:49.383 回答
5

如果您使用的是 C# 8.0,我建议您使用新Span<T>的以提高效率。

这是一个粗略的实现

public unsafe class FastBitmap : IDisposable
{
    private Bitmap _bmp;
    private ImageLockMode _lockmode;
    private int _pixelLength;

    private Rectangle _rect;
    private BitmapData _data;
    private byte* _bufferPtr;

    public int Width { get => _bmp.Width; }
    public int Height { get => _bmp.Height; }
    public PixelFormat PixelFormat { get => _bmp.PixelFormat; }

    public FastBitmap(Bitmap bmp, ImageLockMode lockMode)
    {
        _bmp = bmp;
        _lockmode = lockMode;

        _pixelLength = Image.GetPixelFormatSize(bmp.PixelFormat) / 8;
        _rect = new Rectangle(0, 0, Width, Height);
        _data = bmp.LockBits(_rect, lockMode, PixelFormat);
        _bufferPtr = (byte*)_data.Scan0.ToPointer();
    }

    public Span<byte> this[int x, int y]
    {
        get
        {
            var pixel = _bufferPtr + y * _data.Stride * x * _pixelLength;
            return new Span<byte>(pixel, _pixelLength);
        }
        set
        {
            value.CopyTo(this[x, y]);
        }
    }

    public void Dispose()
    {
        _bmp.UnlockBits(_data);
    }
}
于 2020-01-09T06:55:59.693 回答
4

你想要LockBits。然后,您可以从它提供给您的 BitmapData 对象中提取所需的字节。

于 2009-10-13T21:39:04.567 回答
1

在@notJim 答案的基础上(并在https://web.archive.org/web/20141229164101/http://bobpowell.net/lockingbits.aspx的帮助下),我开发了以下内容,让我的生活变得更轻松我最终得到一个数组数组,允许我通过它的xy坐标跳转到一个像素。当然,x坐标需要通过每个像素的字节数进行校正,但这是一个简单的扩展。

Dim bitmapData As Imaging.BitmapData = myBitmap.LockBits(New Rectangle(0, 0, myBitmap.Width, myBitmap.Height), Imaging.ImageLockMode.ReadOnly, myBitmap.PixelFormat)

Dim size As Integer = Math.Abs(bitmapData.Stride) * bitmapData.Height
Dim data(size - 1) As Byte

Marshal.Copy(bitmapData.Scan0, data, 0, size)

Dim pixelArray(myBitmap.Height)() As Byte

'we have to load all the opacity pixels into an array for later scanning by column
'the data comes in rows
For y = myBitmap.Height - 1 To 0 Step -1
    Dim rowArray(bitmapData.Stride) As Byte
    Array.Copy(data, y * bitmapData.Stride, rowArray, 0, bitmapData.Stride)
    'For x = myBitmap.Width - 1 To 0 Step -1
    '   Dim i = (y * bitmapData.Stride) + (x * 4)
    '   Dim B = data(i)
    '   Dim G = data(i + 1)
    '   Dim R = data(i + 2)
    '   Dim A = data(i + 3)
    'Next
    pixelArray(y) = rowArray
Next
于 2013-02-28T22:54:45.670 回答
1

还有另一种更快、更方便的方法。如果您查看 Bitmap 构造函数,您会发现一个将 IntPtr 作为最后一个参数的构造函数。该 IntPtr 用于保存像素数据。那么你如何使用它呢?

Dim imageWidth As Integer = 1920
Dim imageHeight As Integer = 1080

Dim fmt As PixelFormat = PixelFormat.Format32bppRgb
Dim pixelFormatSize As Integer = Image.GetPixelFormatSize(fmt)

Dim stride As Integer = imageWidth * pixelFormatSize
Dim padding = 32 - (stride Mod 32)
If padding < 32 Then stride += padding

Dim pixels((stride \ 32) * imageHeight) As Integer
Dim handle As GCHandle = GCHandle.Alloc(pixels, GCHandleType.Pinned)
Dim addr As IntPtr = Marshal.UnsafeAddrOfPinnedArrayElement(pixels, 0)

Dim bitmap As New Bitmap(imageWidth, imageHeight, stride \ 8, fmt, addr)

您现在拥有的是一个简单的整数数组和一个引用相同内存的位图。您对整数数组所做的任何更改都将直接影响位图。让我们用一个简单的亮度变换来试试这个。

Public Sub Brightness(ByRef pixels() As Integer, ByVal scale As Single)
    Dim r, g, b As Integer
    Dim mult As Integer = CInt(1024.0f * scale)
    Dim pixel As Integer

    For i As Integer = 0 To pixels.Length - 1
        pixel = pixels(i)
        r = pixel And 255
        g = (pixel >> 8) And 255
        b = (pixel >> 16) And 255

        'brightness calculation
        'shift right by 10 <=> divide by 1024
        r = (r * mult) >> 10
        g = (g * mult) >> 10
        b = (b * mult) >> 10

        'clamp to between 0 and 255
        If r < 0 Then r = 0
        If g < 0 Then g = 0
        If b < 0 Then b = 0
        r = (r And 255)
        g = (g And 255)
        b = (b And 255)

        pixels(i) = r Or (g << 8) Or (b << 16) Or &HFF000000
    Next
End Sub

您可能会注意到我使用了一个小技巧来避免在循环中进行浮点数学运算。这大大提高了性能。当你完成后,你当然需要清理一点......

addr = IntPtr.Zero
If handle.IsAllocated Then
    handle.Free()
    handle = Nothing
End If
bitmap.Dispose()
bitmap = Nothing
pixels = Nothing

我在这里忽略了 alpha 组件,但您也可以随意使用它。我以这种方式组合了很多位图编辑工具。它比 Bitmap.LockBits() 更快、更可靠,最重要的是,它需要零内存复制才能开始编辑位图。

于 2014-05-13T17:51:48.373 回答
0

试试这个 C# 解决方案。

创建一个用于测试的 winforms 应用程序。

添加一个按钮和一个图片框,以及一个单击事件和一个表单关闭事件。

为您的表单使用以下代码:

public partial class Form1 : Form
{
    uint[] _Pixels { get; set; }

    Bitmap _Bitmap { get; set; }

    GCHandle _Handle { get; set; }

    IntPtr _Addr { get; set; }


    public Form1()
    {
        InitializeComponent();

        int imageWidth = 100; //1920;

        int imageHeight = 100; // 1080;

        PixelFormat fmt = PixelFormat.Format32bppRgb;

        int pixelFormatSize = Image.GetPixelFormatSize(fmt);

        int stride = imageWidth * pixelFormatSize;

        int padding = 32 - (stride % 32);

        if (padding < 32)
        {
            stride += padding;
        }

        _Pixels = new uint[(stride / 32) * imageHeight + 1];

         _Handle = GCHandle.Alloc(_Pixels, GCHandleType.Pinned);

        _Addr = Marshal.UnsafeAddrOfPinnedArrayElement(_Pixels, 0);

        _Bitmap = new Bitmap(imageWidth, imageHeight, stride / 8, fmt, _Addr);

        pictureBox1.Image = _Bitmap;

    }

    private void button1_Click(object sender, EventArgs e)
    {
        for (int i = 0; i < _Pixels.Length; i++)
        {
            _Pixels[i] = ((uint)(255 | (255 << 8) | (255 << 16) | 0xff000000));

        }

    }

    private void Form1_FormClosing(object sender, FormClosingEventArgs e)
    {
        _Addr = IntPtr.Zero;

        if (_Handle.IsAllocated)
        {
            _Handle.Free();

        }

        _Bitmap.Dispose();

        _Bitmap = null;

        _Pixels = null;

    }

}

现在,您对数组所做的任何编辑都会自动更新位图。

您需要调用图片框上的刷新方法才能看到这些更改。

于 2016-09-08T10:11:36.210 回答