910122 - problem with DrawImage

ok, let me describe it with another example which contrasts the problem. for regenerating it, please go to Paint and create a 2x2 image and fill it with the black color. then save it as d:\small3.png. now you have a 2x2 image which its entire surface is black. then create a new C# form application in which a picture box inserted with no margin. then use the following code:
void f6(Graphics g)
{
var img = Image.FromFile(@"d:\small3.png");
var srcRect = new Rectangle(0, 0, img.Width, img.Height);
int factor = 400;
var destRect = new Rectangle(0, 0, img.Width * factor, img.Height * factor);
g.DrawRectangle(new Pen(Color.Blue), destRect);
g.DrawImage(img, destRect, srcRect, GraphicsUnit.Pixel);
}

private void pictureBox1_Paint(object sender, PaintEventArgs e)
{
f6(e.Graphics);
}
i expect the entire rectangle inside the blue margins be black while the output is as follows:
http://www.uploadup.com/di-L034.png
why?!
i hope i could describe the problem well.
thx

oh! i found that it depends on the color of the remainder part of the picture box! for example if i add the following code before DrawRectangle:
g.FillRectangle(new SolidBrush(Color.DarkCyan), pictureBox1.ClientRectangle);
the gradient effect which DrawImage causes gets between black to dark cyan!
i also change the srcRect from (0, 0, 2, 2) to (0, 0, 1, 1) and this time DrawImage doesn't produce the gradient effect.
someone describe please :(

oh! i surrender understanding the behavior of DrawImage!
see what happened! with the 2x2 image changed to:
http://www.uploadup.com/di-WCGA.png
and the following code:
void f8(Graphics g)
{
var img = Image.FromFile(@"d:\small3.png");
var srcRect = new Rectangle(0, 0, img.Width, img.Height);
int factor = 50;
int w = img.Width*factor;
g.FillRectangle(new SolidBrush(Color.DarkCyan), pictureBox1.ClientRectangle);
var destRect = new Rectangle(0, 0, 3 * w, w); // assuming img.Width == img.Height
g.FillRectangle(new SolidBrush(Color.Chartreuse), destRect);
destRect.Y = 2*w;
g.FillRectangle(new SolidBrush(Color.Chartreuse), destRect);
destRect.X = 0;
destRect.Y = w;
destRect.Width = w;
g.FillRectangle(new SolidBrush(Color.Chartreuse), destRect);
destRect.X = 2*w;
g.FillRectangle(new SolidBrush(Color.Chartreuse), destRect);
destRect.X = w;
g.DrawImage(img, destRect, srcRect, GraphicsUnit.Pixel);
}
i get the following result:
http://www.uploadup.com/di-OMVI.png
it's weird! consider drawing the image after drawing the margin with color Chartreuse.

and the following code:
void f9(Graphics g)
{
var img = new Bitmap(3, 2);
var memG = Graphics.FromImage(img);
memG.FillRectangle(new SolidBrush(Color.Black), 0, 0, img.Width, img.Height);
GlobalFunctions.PutPixel(memG, new Pen(Color.Red), 1, 0);
GlobalFunctions.PutPixel(memG, new Pen(Color.Blue), 0, 1);
GlobalFunctions.PutPixel(memG, new Pen(Color.GreenYellow), 2, 0);
GlobalFunctions.PutPixel(memG, new Pen(Color.Cyan), 2, 1);
var srcRect = new Rectangle(0, 0, img.Width, img.Height);
int factor = 100;
var destRect = new Rectangle(0, 0, img.Width * factor, img.Height * factor);
g.FillRectangle(new SolidBrush(Color.DarkCyan), pictureBox1.ClientRectangle);
g.DrawRectangle(new Pen(Color.Blue), destRect);
g.DrawImage(img, destRect, srcRect, GraphicsUnit.Pixel);
}
generates the following result:
http://www.uploadup.com/di-0B33.png
no description?
indeed i expect this to be the result of drawing an image which is 4x3 instead of 3x2 which its 3 right points and 4 bottom points be of color dark blue. got what i mean?