CODEWITHSUNDEEP
silverlightpixelbitmapimage
Rafe
Rafe

Reputation: 9275

How can I read a pixel's color from a BitmapImage in Silverlight?

I have a BitmapImage instance in Silverlight, and I am trying to find a way to read the color information of each pixel in the image. How can I do this? I see that there is a CopyPixels() method on this class that writes pixel information into the array that you pass it, but I don't know how to read color information out of that array.

How can I do this?

Upvotes: 1

Views: 3938

Answers (3)

Anton Kedrov
Anton Kedrov

Reputation: 1767

First, you should use WritableBitmap to get pixels collection: WriteableBitmap bmp = new WriteableBitmap(bitmapImageObj);. Each pixel is represented as 32-bit integer. I have made structure, which just helps to splits integer into a four bytes (ARGB).

struct BitmapPixel
{
    public byte A;
    public byte R;
    public byte G;
    public byte B;

    public BitmapPixel(int pixel)
        : this(BitConverter.GetBytes(pixel))
    {
    }

    public BitmapPixel(byte[] pixel)
        : this(pixel[3], pixel[2], pixel[1], pixel[0])
    {
    }

    public BitmapPixel(byte a, byte r, byte g, byte b)
    {
        this.A = a;
        this.R = r;
        this.G = g;
        this.B = b;
    }

    public int ToInt32()
    {
        byte[] pixel = new byte[4] { this.B, this.G, this.R, this.A };
        return BitConverter.ToInt32(pixel, 0);
    }
}

Here is an example of how it could be used to change red value:

BitmapPixel pixel = new BitmapPixel(bmp.Pixels[0]);
pixel.R = 255;
bmp.Pixels[0] = pixel.ToInt32();

Also I would like to mention that WriteableBitmap.Pixels are in Premultiplied RGB format. This article will explain what it means. And here is how compensation done by using BitmapPixel structure:

public static void CompensateRGB(int[] pixels)
{
    for (int i = 0; i < pixels.Length; i++)
    {
        BitmapPixel pixel = new BitmapPixel(pixels[i]);

        if (pixel.A == 255 || pixel.A == 0)
            continue;

        if (pixel.R == 0 && pixel.G == 0 && pixel.B == 0)
        {
            // color is unrecoverable, get rid of this
            // pixel by making it transparent
            pixel.A = 0;
        }
        else
        {
            double factor = 255.0 / pixel.A;

            pixel.A = 255;
            pixel.R = (byte)(pixel.R * factor);
            pixel.G = (byte)(pixel.G * factor);
            pixel.B = (byte)(pixel.B * factor);
        }

        pixels[i] = pixel.ToInt32();
    }
}

Upvotes: 0

Chris
Chris

Reputation: 21

Look for the WriteableBitmap class in Silverlight 3. This class has a member Pixels which returns the bitmap's pixel data in an array of int's.

An example with a transform. bi is an BitmapImage object.

Image img = new Image();
img.source = bi;

img.Measure(new Size(100, 100));
img.Arrange(new Rect(0, 0, 100, 100));

ScaleTransform scaleTrans = new ScaleTransform();
double scale = (double)500 / (double)Math.Max(bi.PixelHeight, bi.PixelWidth);
scaleTrans.CenterX = 0;
scaleTrans.CenterY = 0;
scaleTrans.ScaleX = scale;
scaleTrans.ScaleY = scale;

WriteableBitmap writeableBitmap = new WriteableBitmap(500, 500);
writeableBitmap.Render(img, scaleTrans);

int[] pixelData = writeableBitmap.Pixels;

Upvotes: 2

markti
markti

Reputation: 4518

This is not possible with the current Bitmap API in the currently released Silverlight 3 beta.

The Silverlight BitmapImage file does not have a CopyPixels method. Please see the MSDN documentation here.

Upvotes: 0

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