matrix multiplication in C#

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I have a grayscale 30x40 image and I want to get its equivalent binary format and later multiply it with a 40x1 matrix so that I would be able to sort of compress it. This is the code which allows me to convert to binary, how can put in a matrix and multiply it?

C#

private byte[] toBin(Bitmap b)
        {
                byte[] binVals = new byte[imgSize];
                int k = 0;
                for (int i = 0; i < img.Height; i ++)
                {
                    for (int j = 0; j < img.Width; j ++)
                    {
                        if (img.GetPixel(j, i).A.ToString() == "255" && img.GetPixel(j, i).B.ToString() == "255")
                        {
                            byte z = (byte)0;
                            binVals[k] = z;
                            k++;
                        }
                        else
                        {
                            byte z = (byte)1;
                            binVals[k] = z;
                            k++;
                        }
                    }
                }

                return (binVals);
        }

Posted 29-Nov-12 4:58am

datt265

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E.F. Nijboer 29-Nov-12 11:07am

You might want to change: img.GetPixel(j, i).A.ToString() == "255"
into this: img.GetPixel(j, i).A == 255

Matt T Heffron 29-Nov-12 20:42pm

This appears to be doing a grayscale to black/white conversion with a *very* extreme threshold.
(I don't know your application, but in general, I'd have expected the split to be at the half-intensity value of 128, or the midpoint between the max and min intensity of the input image.)

Why are you putting this into a 1-dimensional array, instead of one the same shape as your input?
The 1-dimensional representation will make the matrix multiplication implementation much more difficult.

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Sergey Alexandrovich Kryukov · Answer 1 · 2012-11-29T06:37:00

You are going nowhere, in terms of performance, which would be killed by your GetPixel/PutPixel. You need to use System.Drawing.Bitmap.LockBits instead:
http://msdn.microsoft.com/en-us/library/system.drawing.bitmap.lockbits.aspx[^].

There is a short and clear code sample on the help page on the first of the methods referenced.

I don't know what's your problem with matrix multiplication; this operation is very simple.

—SA