how to apply gradient effect on Image GDI - c#-4.0

Question

How can I apply gradient effect on image like this image in c#. I have a transparent image with black drawing I want to apply 2 color gradient on the image is this possible in gdi?
Here is the effect i want to achieve
http://postimg.org/image/ikz1ie7ip/

Answer 1

You create a PathGradientBrush and then you draw your texts with that brush.
To create a bitmap filled with a gradient brush you could do something like:
public Bitmap GradientImage(int width, int height, Color color1, Color color2, float angle)
{
var r = new Rectangle(0, 0, width, height);
var bmp = new Bitmap(width, height);
using (var brush = new LinearGradientBrush(r, color1, color2, angle, true))
using (var g = Graphics.FromImage(bmp))
g.FillRectangle(brush, r);
return bmp;
}
So now that you have an image with the gradient in it, all you have to do is to bring over the alpha channel from your original image into the newly created image. We can take the transferOneARGBChannelFromOneBitmapToAnother function from a blog post I once wrote:
public enum ChannelARGB
{
Blue = 0,
Green = 1,
Red = 2,
Alpha = 3
}
public static void transferOneARGBChannelFromOneBitmapToAnother(
Bitmap source,
Bitmap dest,
ChannelARGB sourceChannel,
ChannelARGB destChannel )
{
if ( source.Size!=dest.Size )
throw new ArgumentException();
Rectangle r = new Rectangle( Point.Empty, source.Size );
BitmapData bdSrc = source.LockBits( r, ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb );
BitmapData bdDst = dest.LockBits( r, ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb );
unsafe
{
byte* bpSrc = (byte*)bdSrc.Scan0.ToPointer();
byte* bpDst = (byte*)bdDst.Scan0.ToPointer();
bpSrc += (int)sourceChannel;
bpDst += (int)destChannel;
for ( int i = r.Height * r.Width; i > 0; i-- )
{
*bpDst = *bpSrc;
bpSrc += 4;
bpDst += 4;
}
}
source.UnlockBits( bdSrc );
dest.UnlockBits( bdDst );
}
Now you could do something like:
var newImage = GradientImage( original.Width, original.Height, Color.Yellow, Color.Blue, 45 );
transferOneARGBChannelFromOneBitmapToAnother( original, newImage, ChannelARGB.Alpha, ChannelARGB.Alpha );
And there you are. :-)