CODEWITHSUNDEEP
c#imagebitmapconsole-application
Paul Karam
Paul Karam

Reputation: 4235

Bitmap.GetPixel only returning 0s for R, G and B

I am loading an image inside a Console application using Image.FromFile.
After that, I am casting it to a Bitmap to be able to use the Bitmap.GetPixel() method. Surprisingly, while looping through all the pixels, all what I am getting from the GetPixel is 0,0,0 for R,G,B.

To make sure that the image is well read from the file, I added a reference to System.Windows.Forms and I loaded the image inside a PictureBox to see the result, and the image is well seen.

Original Image:

Original Image

Here's how I am loading the image and showing it into a PictureBox:

Bitmap img = (Bitmap)Image.FromFile("image.png");

PictureBox pb = new PictureBox
{
    Image = img
};

Form frm = new Form
{
    Controls = { pb }
};

frm.ShowDialog();

Which shows the image as it is:

Form shown after calling Form.ShowDialog

And after that, I am getting the pixels like:

byte[] input = new byte[784];

for (int x = 0; x < 28; x++)
{
    for (int y = 0; y < 28; y++)
    {
        Color color = img.GetPixel(x, y);
        byte r = color.R;
        byte g = color.G;
        byte b = color.B;

        Console.Write($"{color.R},{color.G},{color.B}|||");
        input[x * 28 + y] = (byte)((((r + g + b) / 3)));
    }
    Console.WriteLine();
}

Note that the image size is 28x28px, and I have tried other images and I've got the same result.

What I expected that the results shows the real color values since I've used that method before and it worked perfectly, but now all the results printed to the console are zeros which I am finding it difficult to understand.

Edit:

Since the PictureBox is showing the real image representation, I tried to get the pixels from the PictureBox.Image like:

Color color = ((Bitmap)pb.Image).GetPixel(x, y);

This also didn't work and the results came back as zeros.

What could be the reason behind this and how to fix it?

Upvotes: 1

Views: 558

Answers (1)

TaW
TaW

Reputation: 54453

In your image all color channels of all pixels are 0, so you code actually works fine.

And most of the pixels also have an alpha of 0, so they are transparent. Some are semi-transparent, anti-aliased pixels and a few are fully opaque.

Where transparent or semi-transprent pixels are, the backcolor will shine through.

If you want to recognize the really, non-transparent black pixels you need to test the alpha channel as well.

Here is a function that will create a composite color of a pixel's color and a given background color..:

Color Composite(Color color, Color backcolor)
{
    byte r = (byte)(((255 - color.A) * backcolor.R + color.R * color.A) / 256);
    byte g = (byte)(((255 - color.A) * backcolor.G + color.G * color.A) / 256);
    byte b = (byte)(((255 - color.A) * backcolor.B + color.B * color.A) / 256);
    Color c2 = Color.FromArgb(255, r, g, b);
    return c2;
}

If you want the brightness of one of your pixels you could create a composite of its color with white. But, given the image you have, you could just as well use color.A directly..

Upvotes: 1

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