Use same accuracy as other encoders

src/ImageSharp.Formats.Jpeg/JpegDecoderCore.cs

@@ -607,15 +607,15 @@ namespace ImageSharp.Formats
             int ccr = cr - 128;
 
             // Speed up the algorithm by removing floating point calculation
-            // Scale by 1024, add .5F and truncate value. We use bit shifting to divide the result
-            int r0 = 1436 * ccr; // (1.402F * 1024) + .5F
-            int g0 = 352 * ccb; // (0.34414F * 1024) + .5F
-            int g1 = 731 * ccr; // (0.71414F  * 1024) + .5F
-            int b0 = 1815 * ccb; // (1.772F * 1024) + .5F
-
-            byte r = (byte)(y + (r0 >> 10)).Clamp(0, 255);
-            byte g = (byte)(y - (g0 >> 10) - (g1 >> 10)).Clamp(0, 255);
-            byte b = (byte)(y + (b0 >> 10)).Clamp(0, 255);
+            // Scale by 65536, add .5F and truncate value. We use bit shifting to divide the result
+            int r0 = 91881 * ccr; // (1.402F * 65536) + .5F
+            int g0 = 22554 * ccb; // (0.34414F * 65536) + .5F
+            int g1 = 46802 * ccr; // (0.71414F  * 65536) + .5F
+            int b0 = 116130 * ccb; // (1.772F * 65536) + .5F
+
+            byte r = (byte)(y + (r0 >> 16)).Clamp(0, 255);
+            byte g = (byte)(y - (g0 >> 16) - (g1 >> 16)).Clamp(0, 255);
+            byte b = (byte)(y + (b0 >> 16)).Clamp(0, 255);
             packed.PackFromBytes(r, g, b, 255);
         }
 
@@ -962,16 +962,16 @@ namespace ImageSharp.Formats
             int ccr = cr - 128;
 
             // Speed up the algorithm by removing floating point calculation
-            // Scale by 1024, add .5F and truncate value. We use bit shifting to divide the result
-            int r0 = 1436 * ccr; // (1.402F * 1024) + .5F
-            int g0 = 352 * ccb; // (0.34414F * 1024) + .5F
-            int g1 = 731 * ccr; // (0.71414F  * 1024) + .5F
-            int b0 = 1815 * ccb; // (1.772F * 1024) + .5F
+            // Scale by 65536, add .5F and truncate value. We use bit shifting to divide the result
+            int r0 = 91881 * ccr; // (1.402F * 65536) + .5F
+            int g0 = 22554 * ccb; // (0.34414F * 65536) + .5F
+            int g1 = 46802 * ccr; // (0.71414F  * 65536) + .5F
+            int b0 = 116130 * ccb; // (1.772F * 65536) + .5F
 
             // First convert from YCbCr to CMY
-            float cyan = (y + (r0 >> 10)).Clamp(0, 255) / 255F;
-            float magenta = (byte)(y - (g0 >> 10) - (g1 >> 10)).Clamp(0, 255) / 255F;
-            float yellow = (byte)(y + (b0 >> 10)).Clamp(0, 255) / 255F;
+            float cyan = (y + (r0 >> 16)).Clamp(0, 255) / 255F;
+            float magenta = (byte)(y - (g0 >> 16) - (g1 >> 16)).Clamp(0, 255) / 255F;
+            float yellow = (byte)(y + (b0 >> 16)).Clamp(0, 255) / 255F;
 
             // Get keyline
             float keyline = (255 - this.blackImage[xx, yy]) / 255F;

src/ImageSharp.Formats.Jpeg/JpegEncoderCore.cs

@@ -310,22 +310,22 @@ namespace ImageSharp.Formats
                     int b = data[2];
 
                     // Speed up the algorithm by removing floating point calculation
-                    // Scale by 1024, add .5F and truncate value. We use bit shifting to divide the result
-                    int y0 = 306 * r; // (0.299F * 1024) + .5F
-                    int y1 = 601 * g; // (0.587F * 1024) + .5F
-                    int y2 = 117 * b; // (0.114F * 1024) + .5F
-
-                    int cb0 = -172 * r; // (-0.168736F * 1024) + .5F
-                    int cb1 = 339 * g; // (0.331264F * 1024) + .5F
-                    int cb2 = 512 * b; // (0.5F * 1024) + .5F
-
-                    int cr0 = 512 * r; // (0.5F * 1024) + .5F
-                    int cr1 = 429 * g; // (0.418688F * 1024) + .5F
-                    int cr2 = 83 * b; // (0.081312F * 1024) + .5F
-
-                    float yy = (y0 + y1 + y2) >> 10;
-                    float cb = 128 + ((cb0 - cb1 + cb2) >> 10);
-                    float cr = 128 + ((cr0 - cr1 - cr2) >> 10);
+                    // Scale by 65536, add .5F and truncate value. We use bit shifting to divide the result
+                    int y0 = 19595 * r; // (0.299F * 65536) + .5F
+                    int y1 = 38470 * g; // (0.587F * 65536) + .5F
+                    int y2 = 7471 * b; // (0.114F * 65536) + .5F
+
+                    int cb0 = -11057 * r; // (-0.168736F * 65536) + .5F
+                    int cb1 = 21710 * g; // (0.331264F * 65536) + .5F
+                    int cb2 = 32768 * b; // (0.5F * 65536) + .5F
+
+                    int cr0 = 32768 * r; // (0.5F * 65536) + .5F
+                    int cr1 = 27439 * g; // (0.418688F * 65536) + .5F
+                    int cr2 = 5329 * b; // (0.081312F * 65536) + .5F
+
+                    float yy = (y0 + y1 + y2) >> 16;
+                    float cb = 128 + ((cb0 - cb1 + cb2) >> 16);
+                    float cr = 128 + ((cr0 - cr1 - cr2) >> 16);
 
                     int index = j8 + i;