C# - Padding image bytes with white bytes to fill 512 x 512

Question

I'm using Digital Persona SDK to scan fingerprints in wsq format, for requeriment I need 512 x 512 image, the SDK only export 357 x 392 image.

The sdk provide a method to compress captured image from device in wsq format and return a byte array that I can write to disk.

-I've tried to allocate a buffer of 262144 for 512 x 512 image.

-Fill the new buffer with white pixel data each byte to value 255.

-Copy the original image buffer into the new image buffer. The original image doesn’t need to be centered but it's important to make sure to copy without corrupting the image data.

To summarize I've tried to copy the old image into the upper right corner of the new image.

DPUruNet.Compression.Start();
DPUruNet.Compression.SetWsqBitrate(95, 0);

Fid capturedImage = captureResult.Data;

//Fill the new buffer with white pixel data each byte to value 255.
byte[] bytesWSQ512 = new byte[262144];
for (int i = 0; i < bytesWSQ512.Length; i++)
{
    bytesWSQ512[i] = 255;
}

//Compress capturedImage and get bytes (357 x 392)
byte[] bytesWSQ = DPUruNet.Compression.CompressRaw(capturedImage.Views[0].Width, capturedImage.Views[0].Height, 500, 8, capturedImage.Views[0].RawImage, CompressionAlgorithm.COMPRESSION_WSQ_NIST);

//Copy the original image buffer into the new image buffer
for (int i = 0; i < capturedImage.Views[0].Height; i++)
{
    for (int j = 0; j < capturedImage.Views[0].Width; j++)
    {
        bytesWSQ512[i * bytesWSQ512.Length + j ] = bytesWSQ[i * capturedImage.Views[0].Width + j];
    }
}
//Write bytes to disk
File.WriteAllBytes(@"C:\Users\Admin\Desktop\bytesWSQ512.wsq", bytesWSQ512);
DPUruNet.Compression.Finish();

When running that snippet I get IndexOutOfRangeException, I don't know if the loop or the calculation of indexes for new array are right.

Here is a representation of what I'm trying to do.

`bytesWSQ512[i * bytesWSQ512.Length + j ]` - doesn't look correct. Have you tried debugging your code and inspecting your variables? Don't you mean `i * 512 + j`? — CodeCaster, May 07 '19 at 15:32
You've already stated that `bytesWSQ` is 357 x 392 pixels. Your `for` loop moves beyond the bounds of this, hence the `IndexOutOfRangeException`. Some simple debugging would show you this... What position in the array are you trying to access when the exception occurs? — Martin, May 07 '19 at 15:35
Possible duplicate of [What is an IndexOutOfRangeException / ArgumentOutOfRangeException and how do I fix it?](https://stackoverflow.com/questions/20940979/what-is-an-indexoutofrangeexception-argumentoutofrangeexception-and-how-do-i-f) — , May 07 '19 at 15:36
I debugged but it breaks in different times: 1) i: 26 j = 277 bytesWSQ512 [13312277] = bytesWSQ [9282277] 2) i: 28 j = 61 bytesWSQ512 [1433661] = bytesWSQ [999661] 3) i: 27 j = 143 bytesWSQ512 [13824143] = bytesWSQ [9639143] Maybe the formula to padding the small image bytes to big image is not ok? — jhuamanchumo, May 07 '19 at 16:34

score 0 · Accepted Answer · answered Jun 18 '19 at 21:45

If someone is trying to achieve something like this or padding a raw image, I hope this will help.

DPUruNet.Compression.
DPUruNet.Compression.SetWsqBitrate(75, 0);
Fid ISOFid = captureResult.Data;

byte[] paddedImage = PadImage8BPP(captureResult.Data.Views[0].RawImage, captureResult.Data.Views[0].Width, captureResult.Data.Views[0].Height, 512, 512, 255);
byte[] bytesWSQ512 = Compression.CompressRaw(512, 512, 500, 8, paddedImage, CompressionAlgorithm.COMPRESSION_WSQ_NIST);

And the method to resize (pad) the image is:

public byte[] PadImage8BPP(byte[] original, int original_width, int original_height, int desired_width, int desired_height, byte pad_color)
    {
        byte[] canvas_8bpp = new byte[desired_width * desired_height];

        for (int i = 0; i < canvas_8bpp.Length; i++)
            canvas_8bpp[i] = pad_color; //Fill background.  Note this type of fill will fail histogram checks.

        int clamp_y_begin = 0;
        int clamp_y_end = original_height;
        int clamp_x_begin = 0;
        int clamp_x_end = original_width;

        int pad_y = 0;
        int pad_x = 0;

        if (original_height > desired_height)
        {
            int crop_distance = (int)Math.Ceiling((original_height - desired_height) / 2.0);
            clamp_y_begin = crop_distance;
            clamp_y_end = original_height - crop_distance;
        }
        else
        {
            pad_y = (desired_height - original_height) / 2;
        }

        if (original_width > desired_width)
        {
            int crop_distance = (int)Math.Ceiling((original_width - desired_width) / 2.0);
            clamp_x_begin = crop_distance;
            clamp_x_end = original_width - crop_distance;
        }
        else
        {
            pad_x = (desired_width - original_width) / 2;
        }

        //We traverse the captured image (either whole image or subset)
        for (int y = clamp_y_begin; y < clamp_y_end; y++)
        {
            for (int x = clamp_x_begin; x < clamp_x_end; x++)
            {
                byte image_pixel = original[y * original_width + x];
                canvas_8bpp[(pad_y + y - clamp_y_begin) * desired_width + pad_x + x - clamp_x_begin] = image_pixel;
            }
        }

        return canvas_8bpp;
    }

C# - Padding image bytes with white bytes to fill 512 x 512

1 Answers1