C#图片处理之：色彩调整 .

其原理是每个象素的三个颜色分量同时增加或减少一个固定的值。现在更进一步，假如每个象素三个分量增加或减少的值不是相同的呢？嗯，这就今天要讨论的主题了。

应该很容易想明白，假如我们需要一张照片偏红一点，那只需要每个象素的红色分量值都增加就可以了。举个更实际一点的场景，比如要把一张鲜艳的彩色照片处理成泛棕的老旧黑白照，最简单的一个方法就是先把它处理成256级灰阶图，然后增加每个象素的红色分量。

老规矩，给出函数。

        /**//// <summary>
        /// 色彩调整
        /// </summary>
        /// <param name="bmp">原始图</param>
        /// <param name="rVal">r增量</param>
        /// <param name="gVal">g增量</param>
        /// <param name="bVal">b增量</param>
        /// <returns>处理后的图</returns>
        public static Bitmap KiColorBalance(Bitmap bmp, int rVal, int gVal, int bVal)
        ...{

            if (bmp == null)
            ...{
                return null;
            }


            int h = bmp.Height;
            int w = bmp.Width;

            try
            ...{
                if (rVal > 255 || rVal < -255 || gVal > 255 || gVal < -255 || bVal > 255 || bVal < -255)
                ...{
                    return null;
                }

                BitmapData srcData = bmp.LockBits(new Rectangle(0, 0, w, h), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

                unsafe
                ...{
                    byte* p = (byte*)srcData.Scan0.ToPointer();

                    int nOffset = srcData.Stride - w * 3;
                    int r, g, b;

                    for (int y = 0; y < h; y++)
                    ...{
                        for (int x = 0; x < w; x++)
                        ...{

                            b = p[0] + bVal;
                            if (bVal >= 0)
                            ...{
                                if (b > 255) b = 255;
                            }
                            else
                            ...{
                                if (b < 0) b = 0;
                            }

                            g = p[1] + gVal;
                            if (gVal >= 0)
                            ...{
                                if (g > 255) g = 255;
                            }
                            else
                            ...{
                                if (g < 0) g = 0;
                            }

                            r = p[2] + rVal;
                            if (rVal >= 0)
                            ...{
                                if (r > 255) r = 255;
                            }
                            else
                            ...{
                                if (r < 0) r = 0;
                            }

                            p[0] = (byte)b;
                            p[1] = (byte)g;
                            p[2] = (byte)r;

                            p += 3;
                        }

                        p += nOffset;


                    }
                } // end of unsafe

                bmp.UnlockBits(srcData);

                return bmp;
            }
            catch
            ...{
                return null;
            }

        } // end of color