【C#.NET】LockBitsはGraphic.DrawImageに勝てるのか？

ポケモンスリープに課金したあんみんどうふです。

大量のBitmapを結合するためにGraphic.DrawImageでひたすら描画していたのですが、.NET備え付けの描画関連の処理は遅いものが多い印象が強いです(Bitmap.GetPixel、Bitmap.SetPixel、Bitmap.Clone等)。

もしかしてGraphicsも高速化できたり？と思い、LockBitsを使ったメモリ展開処理でGraphic.DrawImageを再現し、速度を比較してみようと思います。

とりあえずそれっぽく作る

フォームアプリケーションに600×600のPictureBoxを2つ置き、pictureBox1にはGraphics.DrawImage、pictureBox2にはLockBitsで描画した画像をセットしています。

サンプル画像として、いらすとや様から拝借した「ホログラムシールのイラスト」を使用しています。
正方形っぽくていい感じの画像が欲しかったもので。大きさは400×400とちょうどいい。

using System;
using System.Diagnostics;
using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;
using System.Windows.Forms;

private void Form1_Load(object sender, EventArgs e)
{
    Stopwatch sw = new Stopwatch();
    Bitmap bmp = Properties.Resources.image;

    // Graphics.DrawImageで描画
    sw.Start();
    Bitmap drawImage = new Bitmap(pictureBox1.Width, pictureBox1.Height);
    using (Graphics g = Graphics.FromImage(drawImage))
        g.DrawImage(bmp, 0, 0);
    sw.Stop();

    Debug.WriteLine($"DrawImage: {sw.ElapsedMilliseconds}ms");
    pictureBox1.Image = Properties.Resources.image;

    // Bitmapのロック
    sw.Restart();
    BitmapData bmpData = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);

    // ピクセルデータをbyte配列で取得
    byte[] bmpPixels = new byte[bmpData.Stride * bmpData.Height];
    Marshal.Copy(bmpData.Scan0, bmpPixels, 0, bmpPixels.Length);
    bmp.UnlockBits(bmpData);

    // 表示用のBitmapにセット
    Bitmap res = new Bitmap(pictureBox1.Width, pictureBox1.Height);
    BitmapData resData = res.LockBits(new Rectangle(0, 0, res.Width, res.Height), ImageLockMode.WriteOnly, PixelFormat.Format32bppArgb);
    byte[] resPixels = new byte[resData.Stride * resData.Height];
    Marshal.Copy(resData.Scan0, resPixels, 0, resPixels.Length);
    for (int y = 0; y < bmpData.Height; y++)
    {
        for (int x = 0; x < bmpData.Width; x++)
        {
            resPixels[y * resData.Stride + x * 4 + 0] = bmpPixels[y * bmpData.Stride + x * 4 + 0]; // B
            resPixels[y * resData.Stride + x * 4 + 1] = bmpPixels[y * bmpData.Stride + x * 4 + 1]; // G
            resPixels[y * resData.Stride + x * 4 + 2] = bmpPixels[y * bmpData.Stride + x * 4 + 2]; // R
            resPixels[y * resData.Stride + x * 4 + 3] = bmpPixels[y * bmpData.Stride + x * 4 + 3]; // A
        }
    }
    Marshal.Copy(resPixels, 0, resData.Scan0, resPixels.Length);
    res.UnlockBits(resData);
    sw.Stop();

    Debug.WriteLine($"LockBits: {sw.ElapsedMilliseconds}ms");
    pictureBox2.Image = res;
}

using System;

using System.Diagnostics;

using System.Drawing;

using System.Drawing.Imaging;

using System.Runtime.InteropServices;

using System.Windows.Forms;

private void Form1_Load(object sender, EventArgs e)

{

Stopwatch sw = new Stopwatch();

Bitmap bmp = Properties.Resources.image;

// Graphics.DrawImageで描画

sw.Start();

Bitmap drawImage = new Bitmap(pictureBox1.Width, pictureBox1.Height);

using (Graphics g = Graphics.FromImage(drawImage))

g.DrawImage(bmp, 0, 0);

sw.Stop();

Debug.WriteLine($"DrawImage: {sw.ElapsedMilliseconds}ms");

pictureBox1.Image = Properties.Resources.image;

// Bitmapのロック

sw.Restart();

BitmapData bmpData = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);

// ピクセルデータをbyte配列で取得

byte[] bmpPixels = new byte[bmpData.Stride * bmpData.Height];

Marshal.Copy(bmpData.Scan0, bmpPixels, 0, bmpPixels.Length);

bmp.UnlockBits(bmpData);

// 表示用のBitmapにセット

Bitmap res = new Bitmap(pictureBox1.Width, pictureBox1.Height);

BitmapData resData = res.LockBits(new Rectangle(0, 0, res.Width, res.Height), ImageLockMode.WriteOnly, PixelFormat.Format32bppArgb);

byte[] resPixels = new byte[resData.Stride * resData.Height];

Marshal.Copy(resData.Scan0, resPixels, 0, resPixels.Length);

for (int y = 0; y < bmpData.Height; y++)

{

for (int x = 0; x < bmpData.Width; x++)

{

resPixels[y * resData.Stride + x * 4 + 0] = bmpPixels[y * bmpData.Stride + x * 4 + 0]; // B

resPixels[y * resData.Stride + x * 4 + 1] = bmpPixels[y * bmpData.Stride + x * 4 + 1]; // G

resPixels[y * resData.Stride + x * 4 + 2] = bmpPixels[y * bmpData.Stride + x * 4 + 2]; // R

resPixels[y * resData.Stride + x * 4 + 3] = bmpPixels[y * bmpData.Stride + x * 4 + 3]; // A

}

Marshal.Copy(resPixels, 0, resData.Scan0, resPixels.Length);

res.UnlockBits(resData);

sw.Stop();

Debug.WriteLine($"LockBits: {sw.ElapsedMilliseconds}ms");

pictureBox2.Image = res;

}

色も位置も200pxの余白も遜色なく、無事完コピです。

速度は以下の通り。

Graphic.DrawImage	1ms
LockBits	4ms

なんと意外にもDrawImageの方が早かった…。

関数化して10000回実行

回数を重ねれば変わってくるのでは？と思い検証してみます。

/// <summary>
/// LockBitsでBitmapへ描画する
/// </summary>
/// <param name="canvas">描画元</param>
/// <param name="image">描画する画像</param>
/// <param name="pos">座標</param>
/// <returns></returns>
private Bitmap DrawImageWithLockBits(Bitmap canvas, Bitmap image, Point pos)
{
    // 描画する画像をロック
    BitmapData imageData = image.LockBits(new Rectangle(0, 0, image.Width, image.Height), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);

    // ピクセルデータをbyte配列で取得
    byte[] imagePixels = new byte[imageData.Stride * imageData.Height];
    Marshal.Copy(imageData.Scan0, imagePixels, 0, imagePixels.Length);
    image.UnlockBits(imageData);

    // 描画対象へ描画
    BitmapData canvasData = canvas.LockBits(new Rectangle(0, 0, canvas.Width, canvas.Height), ImageLockMode.WriteOnly, PixelFormat.Format32bppArgb);
    byte[] canvasPixels = new byte[canvasData.Stride * canvasData.Height];
    Marshal.Copy(canvasData.Scan0, canvasPixels, 0, canvasPixels.Length);

    int width = canvas.Width;
    int height = canvas.Height;
    for (int y = 0; y < imageData.Height; y++)
    {
        for (int x = 0; x < imageData.Width; x++)
        {
            int pixel = (y + pos.Y) * canvasData.Stride + (x + pos.X) * 4;

            // 描画元の範囲内、配列の範囲内のみ値の代入を行う
            if (x + pos.X < width && y + pos.Y < height && pixel < canvasPixels.Length)
            {
                canvasPixels[pixel + 0] = imagePixels[y * imageData.Stride + x * 4 + 0]; // B
                canvasPixels[pixel + 1] = imagePixels[y * imageData.Stride + x * 4 + 1]; // G
                canvasPixels[pixel + 2] = imagePixels[y * imageData.Stride + x * 4 + 2]; // R
                canvasPixels[pixel + 3] = imagePixels[y * imageData.Stride + x * 4 + 3]; // A
            }
        }
    }
    Marshal.Copy(canvasPixels, 0, canvasData.Scan0, canvasPixels.Length);
    canvas.UnlockBits(canvasData);

    return canvas;
}

private Bitmap DrawImageWithLockBits(Bitmap canvas, Bitmap image, int x = 0, int y = 0)
{
    return DrawImageWithLockBits(canvas, image, new Point(x, y));
}

/// <summary>

/// LockBitsでBitmapへ描画する

/// </summary>

/// <param name="canvas">描画元</param>

/// <param name="image">描画する画像</param>

/// <param name="pos">座標</param>

/// <returns></returns>

private Bitmap DrawImageWithLockBits(Bitmap canvas, Bitmap image, Point pos)

{

// 描画する画像をロック

BitmapData imageData = image.LockBits(new Rectangle(0, 0, image.Width, image.Height), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);

// ピクセルデータをbyte配列で取得

byte[] imagePixels = new byte[imageData.Stride * imageData.Height];

Marshal.Copy(imageData.Scan0, imagePixels, 0, imagePixels.Length);

image.UnlockBits(imageData);

// 描画対象へ描画

BitmapData canvasData = canvas.LockBits(new Rectangle(0, 0, canvas.Width, canvas.Height), ImageLockMode.WriteOnly, PixelFormat.Format32bppArgb);

byte[] canvasPixels = new byte[canvasData.Stride * canvasData.Height];

Marshal.Copy(canvasData.Scan0, canvasPixels, 0, canvasPixels.Length);

int width = canvas.Width;

int height = canvas.Height;

for (int y = 0; y < imageData.Height; y++)

{

for (int x = 0; x < imageData.Width; x++)

{

int pixel = (y + pos.Y) * canvasData.Stride + (x + pos.X) * 4;

// 描画元の範囲内、配列の範囲内のみ値の代入を行う

if (x + pos.X < width && y + pos.Y < height && pixel < canvasPixels.Length)

{

canvasPixels[pixel + 0] = imagePixels[y * imageData.Stride + x * 4 + 0]; // B

canvasPixels[pixel + 1] = imagePixels[y * imageData.Stride + x * 4 + 1]; // G

canvasPixels[pixel + 2] = imagePixels[y * imageData.Stride + x * 4 + 2]; // R

canvasPixels[pixel + 3] = imagePixels[y * imageData.Stride + x * 4 + 3]; // A

}

Marshal.Copy(canvasPixels, 0, canvasData.Scan0, canvasPixels.Length);

canvas.UnlockBits(canvasData);

return canvas;

}

private Bitmap DrawImageWithLockBits(Bitmap canvas, Bitmap image, int x = 0, int y = 0)

{

return DrawImageWithLockBits(canvas, image, new Point(x, y));

}

これをフォームのLoadイベントでDrawImageと共に10000回実行させます。

Stopwatch sw = new Stopwatch();
Bitmap bmp = Properties.Resources.image;

// DrawImageを使用して描画
Bitmap drawImage = new Bitmap(pictureBox1.Width, pictureBox1.Height);
sw.Start();
using (Graphics g = Graphics.FromImage(drawImage))
    for (int i = 0; i < 10000; i++)
        g.DrawImage(bmp, 0, 0);
pictureBox1.Image = drawImage;
sw.Stop();
Debug.WriteLine($"DrawImage: {sw.ElapsedMilliseconds}ms");

// LockBitsを使用して描画
Bitmap lockBits = new Bitmap(pictureBox2.Width, pictureBox2.Height);
sw.Restart();
for (int i = 0; i < 10000; i++)
    lockBits = DrawImageWithLockBits(lockBits, bmp, 0, 0);
pictureBox2.Image = lockBits;
sw.Stop();
Debug.WriteLine($"LockBits: {sw.ElapsedMilliseconds}ms");

Stopwatch sw = new Stopwatch();

Bitmap bmp = Properties.Resources.image;

// DrawImageを使用して描画

Bitmap drawImage = new Bitmap(pictureBox1.Width, pictureBox1.Height);

sw.Start();

using (Graphics g = Graphics.FromImage(drawImage))

for (int i = 0; i < 10000; i++)

g.DrawImage(bmp, 0, 0);

pictureBox1.Image = drawImage;

sw.Stop();

Debug.WriteLine($"DrawImage: {sw.ElapsedMilliseconds}ms");

// LockBitsを使用して描画

Bitmap lockBits = new Bitmap(pictureBox2.Width, pictureBox2.Height);

sw.Restart();

for (int i = 0; i < 10000; i++)

lockBits = DrawImageWithLockBits(lockBits, bmp, 0, 0);

pictureBox2.Image = lockBits;

sw.Stop();

Debug.WriteLine($"LockBits: {sw.ElapsedMilliseconds}ms");

結果は以下の通り。

Graphics.DrawImage	5056ms
LockBits	32815ms

勝てません！対戦ありがとうございました！以上！