How Can I Speed Up Bitmap Manipulation in C# Beyond `SetPixel` and `GetPixel`?

Optimizing C# Bitmap Manipulation: Alternatives to Slow SetPixel and GetPixel

Introduction

The built-in GetPixel and SetPixel methods in C# for bitmap manipulation are notoriously slow, especially when dealing with larger images. This article presents superior alternatives for significantly enhanced performance.

High-Performance Alternatives

Three primary methods offer substantial speed improvements over the standard functions:

1. DirectBitmap Class: This custom class provides direct, unmanaged access to bitmap data, eliminating the overhead of locking and copying. It offers GetPixel and SetPixel methods for intuitive pixel manipulation.

2. LockBits Method: This built-in method locks a section of the bitmap in memory for direct access to its raw data. While faster than SetPixel/GetPixel, it requires explicit locking and unlocking, introducing a small performance cost.

3. Unsafe Code Blocks: This approach utilizes unsafe pointers for direct memory manipulation. While potentially the fastest, it demands careful handling to prevent memory corruption; this method is best suited for experienced developers.

Performance Benchmarks

Performance varies depending on image size and the specific operation. Generally, DirectBitmap surpasses LockBits and dramatically outperforms SetPixel/GetPixel for larger bitmaps. The following table illustrates the performance differences:

Method	4x4	16x16	64x64	256x256	1024x1024	4096x4096
DirectBitmap		2	28	668	8219	178639
LockBits	2	3	33	670	9612	197115
SetPixel	45	371	5920	97477	1563171	25811013

Code Sample: DirectBitmap

The DirectBitmap class simplifies pixel access:

public void SetPixel(int x, int y, Color colour)
public Color GetPixel(int x, int y)

Usage example:

var dbm = new DirectBitmap(width, height);
dbm.SetPixel(x, y, Color.Red);
Color c = dbm.GetPixel(x, y);

Conclusion

For optimal performance with large bitmaps, the DirectBitmap class provides a compelling solution, offering significant speed improvements over traditional methods. LockBits presents a balanced compromise between speed and ease of use, while unsafe code, though potentially fastest, demands careful implementation.

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