C#图片处理之:亮度和对比度的校正

亮度和对比度应该是最常见的处理要求了。就算是N年前9寸黑白电视机也必有这两个旋钮。

亮度调整算法很简单。对每一个像素的RGB值同时加上或减去一个特定的值就可以了。当然由于RGB取值范围都是在[0，255]的，所以要考虑到越界的问题。

        /**//// <summary>
        /// 图像明暗调整
        /// </summary>
        /// <param name="b">原始图</param>
        /// <param name="degree">亮度[-255, 255]</param>
        /// <returns></returns>
        public static Bitmap KiLighten(Bitmap b, int degree)
        ...{
            if (b == null)
            ...{
                return null;
            }

            if (degree < -255) degree = -255;
            if (degree > 255) degree = 255;

            try
            ...{

                int width = b.Width;
                int height = b.Height;

                int pix = 0;

                BitmapData data = b.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

                unsafe
                ...{
                    byte* p = (byte*)data.Scan0;
                    int offset = data.Stride - width * 3;
                    for (int y = 0; y < height; y++)
                    ...{
                        for (int x = 0; x < width; x++)
                        ...{
                            // 处理指定位置像素的亮度
                            for (int i = 0; i < 3; i++)
                            ...{
                                pix = p[i] + degree;

                                if (degree < 0) p[i] = (byte)Math.Max(0, pix);
                                if (degree > 0) p[i] = (byte)Math.Min(255, pix);

                            } // i
                            p += 3;
                        } // x
                        p += offset;
                    } // y
                }

                b.UnlockBits(data);

                return b;
            }
            catch
            ...{
                return null;
            }

        } // end of Lighten

对比度校正的思想也很简单，大的原则就是让亮的更亮，暗的更暗。具体实现的方式有很多种，比如取一个阀值，超过的就加一定的值，不到的就减一定的值等等。

        /**//// <summary>
        /// 图像对比度调整
        /// </summary>
        /// <param name="b">原始图</param>
        /// <param name="degree">对比度[-100, 100]</param>
        /// <returns></returns>
        public static Bitmap KiContrast(Bitmap b, int degree)
        ...{
            if (b == null)
            ...{
                return null;
            }

            if (degree < -100) degree = -100;
            if (degree > 100) degree = 100;

            try
            ...{

                double pixel = 0;
                double contrast = (100.0 + degree) / 100.0;
                contrast *= contrast;
                int width = b.Width;
                int height = b.Height;
                BitmapData data = b.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
                unsafe
                ...{
                    byte* p = (byte*)data.Scan0;
                    int offset = data.Stride - width * 3;
                    for (int y = 0; y < height; y++)
                    ...{
                        for (int x = 0; x < width; x++)
                        ...{
                            // 处理指定位置像素的对比度
                            for (int i = 0; i < 3; i++)
                            ...{
                                pixel = ((p[i] / 255.0 - 0.5) * contrast + 0.5) * 255;
                                if (pixel < 0) pixel = 0;
                                if (pixel > 255) pixel = 255;
                                p[i] = (byte)pixel;
                            } // i
                            p += 3;
                        } // x
                        p += offset;
                    } // y
                }
                b.UnlockBits(data);
                return b;
            }
            catch
            ...{
                return null;
            }
        } // end of Contrast