CODEWITHSUNDEEP
c#.net
Joe B
Joe B

Reputation: 883

Graphics.DrawImage() Creates a Blank Image

I'm trying to use Graphics.DrawImage() to copy a portion of a bitmap; however, the copy is a blank image. Each pixel has a zero value. To debug the problem, I created a simple unit test demonstrating the issue.

Why are all the pixels 0 in the new bitmap?

    [Test]
    public void CopyImage()
    {
        // Create a dummy bitmap using a counter.
        Bitmap bitmap = new Bitmap(3, 3);
        int color = 0;

        for (int y = 0; y < 3; y++)
        {
            for (int x = 0; x < 3; x++)
            {
                bitmap.SetPixel(x, y, Color.FromArgb(color));
                color++;
            }
        }

        // Copy the bitmap
        Bitmap newBitmap = new Bitmap(3, 3);
        Graphics g = Graphics.FromImage(newBitmap);
        g.DrawImage(bitmap, new Point(0, 0));
        g.Save();

        // Validate the bitmap was copied correctly.
        // All pixels have an ARGB value of 0 so the
        // asserts fail.
        color = 0;

        for (int y = 0; y < 3; y++)
        {
            for (int x = 0; x < 3; x++)
            {
                Assert.AreEqual(color, newBitmap.GetPixel(x, y).ToArgb());
                color++;
            }
        }
    }

Upvotes: 0

Views: 965

Answers (1)

Clive Ciappara
Clive Ciappara

Reputation: 558

I think the color value passed to Color.FromArgb(color) has to be bigger than 0,1,2 to be visible like this hexadecimal if using one parameter:

Color.FromArgb(0x78FF0000)

Else pass three values for red, green, blue between 0 and 255 and use values like 0, 100, 200 to see a difference:

Color.FromArgb(255, 0, 0)

Upvotes: 3

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