Comparing BMP files?

Question

I want to compare two bmp files. I was thinking of two approaches:

• to compare the header, as well as the header of the information of the two files.
• convert the bmp file to binary, and then do the above comparison.

But I do not know where to start, and which will be the best approach. I would be happy if someone could help me!

Answer 1

I don’t know which platform you want to implement this on, but here are some code snippets that may be useful:

Compare two images with C #

2 , . , . , , .

/// <summary>
/// method for comparing 2 images to see if they are the same. First
/// we convert both images to a byte array, we then get their hash (their
/// hash should match if the images are the same), we then loop through
/// each item in the hash comparing with the 2nd Bitmap
/// </summary>
/// <param name="bmp1"></param>
/// <param name="bmp2"></param>
/// <returns></returns>
public bool doImagesMatch(ref Bitmap bmp1, ref Bitmap bmp2)
{
  ...
}

Answer 2

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Answer 3

.NET 3.0+ , :

    public static bool Compare(this Bitmap bmp1, Bitmap bmp2)
    {
        //put your comparison logic here
    }

Answer 4

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Answer 5

, , - 32bpp, 8bpp. , , LockBits 32bpp, Marshal.Copy(), , .

/// <summary>
/// Compares two images for pixel equality
/// </summary>
/// <param name="fname1">first image file</param>
/// <param name="fname2">second image file</param>
/// <returns>true if images are identical</returns>
public static string PageCompare(string fname1, string fname2) {
    try {
        using (Bitmap bmp1 = new Bitmap(fname1))
        using (Bitmap bmp2 = new Bitmap(fname2)) {
            if (bmp1.Height != bmp2.Height || bmp1.Width != bmp2.Width)
                return false;

            // Convert image to int32 array with each int being one pixel
            int cnt = bmp1.Width * bmp1.Height * 4 / 4;
            BitmapData bmData1 = bmp1.LockBits(new Rectangle(0, 0, bmp1.Width, bmp1.Height),
                ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);
            BitmapData bmData2 = bmp2.LockBits(new Rectangle(0, 0, bmp2.Width, bmp2.Height),
                ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);

            Int32[] rgbValues1 = new Int32[cnt];
            Int32[] rgbValues2 = new Int32[cnt];

            // Copy the ARGB values into the array.
            System.Runtime.InteropServices.Marshal.Copy(bmData1.Scan0, rgbValues1, 0, cnt);
            System.Runtime.InteropServices.Marshal.Copy(bmData2.Scan0, rgbValues2, 0, cnt);

            bmp1.UnlockBits(bmData1);
            bmp2.UnlockBits(bmData2);
            for (int i = 0; i < cnt; ++i) {
                if (rgbValues1[i] != rgbValues2[i])
                    return false;
            }
        }
    }
    catch (Exception ex) {
        return false;
    }
    // We made it this far so the images must match
    return true;
}