C# - Tabulating Image orientation values

I have an Image and want to rotate it with an Angle ranging from 9-0.025 to 0.025 in stepping order of 0.001. After each rotation, I multiply the rotated image to its reflection and calculate the total value of all pixels in the Masked image.

I want to tabulate the total pixel values and the corresponding angle of rotation so that I can find the maximum value and at what angle. Since the image resolution is high, what is the best method to compute this ?

original Image: NOTE: [Image is Format8bppIndexed]

Here is my method so far as test:

    RotateBilinear Rotfilter = new RotateBilinear(0.025, true);
    // Rotate by 0.025, keep original image size
    Bitmap RotBlob = Rotfilter.Apply(biggestBlobsImage);
    RotBlob.Save("C:\\Users\\asukumari\\Desktop\\After-X-rotflip.bmp");
    RotBlob.RotateFlip(RotateFlipType.Rotate180FlipX);//Reflect
    RotBlob.Save("C:\\Users\\asukumari\\Desktop\\Reflect.bmp");
                        //---Mask Image---//
    Bitmap i1 = new Bitmap("C:\\Users\\asukumari\\Desktop\\After-X-rotflip.bmp");
    Bitmap i2 = new Bitmap("C:\\Users\\asukumari\\Desktop\\Reflect.bmp");
    Bitmap MskImg = MaskImage(i1, i2);
    MskImg.Save("C:\\Users\\asukumari\\Desktop\\MskImg.bmp");//Mask Image save
                        //-----End---//

Image after rotating by 0.025 degrees: Reflection of previous Image: Mask of both [ImageMultiply]: