c# bitmap question

Sorry for the previous post. I now show the full code here. I need to know what the bitmap.Width and bitmap.Height - 1 for and also the bitmap.Scan0. I search in the internet but it does not give any full explanation for that. I will appreciate anyone who can briefly explain the whole thing. Thank you.

public static double[][] GetRgbProjections(Bitmap bitmap)
        {
            var width = bitmap.Width - 1;
            var height = bitmap.Height - 1;

            var horizontalProjection = new double[width];
            var verticalProjection = new double[height];

            var bitmapData1 = bitmap.LockBits(new Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);

            u开发者_运维知识库nsafe
            {
                var imagePointer1 = (byte*)bitmapData1.Scan0;

                for (var y = 0; y < height; y++)
                {
                    for (var x = 0; x < width; x++)
                    {
                        var blu = imagePointer1[0];
                        var green = imagePointer1[1];
                        var red = imagePointer1[2];

                        int luminosity = (byte)(((0.2126 * red) + (0.7152 * green)) + (0.0722 * blu));

                        horizontalProjection[x] += luminosity;
                        verticalProjection[y] += luminosity;

                        imagePointer1 += 4;
                    } 

                    imagePointer1 += bitmapData1.Stride - (bitmapData1.Width * 4);
                }
            }

            MaximizeScale(ref horizontalProjection, height);
            MaximizeScale(ref verticalProjection, width);

            var projections = 
                new[]
                    {
                        horizontalProjection, 
                        verticalProjection
                    };

            bitmap.UnlockBits(bitmapData1);
            return projections;
        }

Apparently it runs through every pixel of a RGBA bitmap and calculates the luminosity per pixel which its tracks inside two arrays, luminosity per horizontal line and luminosity per vertical line.

Unless I am mistaken, the -1 should not even be there. When you have a bitmap of 100x100 you want to create an array with 100 elements, not an array with 99 elements (width-1) since you want to track every horizontal and vertical line.