GetPixel color is slightly wrong!

ashesman

Hi all,

I am writing a C# .net data plotting application. I use Graphics.DrawLine() to draw my pretty plot lines. Then in the MouseMove event I use a call to windows API GetPixel() (code below) to read the pixel under the mouse. If it is the same color as one of the plot lines I highlight that line next time it is drawn... pretty simple stuff!

The problem is that this works perfectly on my home PC, but on my work PC there is a discrepancy between the colour of the drawn line and the colour I read using GetPixel(). I am not sure if the line is drawn with the wrong color, or the wrong color is read! Eg I write a colour like A=255, R=255, G=128, B= 128 and I read a colour like A=255, R=255, G=132, B=132. There is no problem with standard colours like white, red, black etc...

Any help would be greatly appreciated...


Color color = Color.Empty;
if (control != null)
{
IntPtr hDC = GetDC(control.Handle);
int colorRef = GetPixel(hDC, x, y);
color = Color.FromArgb(
(int)(colorRef & 0x000000FF),
(int)(colorRef & 0x0000FF00) >> 8,
(int)(colorRef & 0x00FF0000) >> 16);
//color = ColorTranslator.FromWin32(colorRef);
ReleaseDC(control.Handle, hDC);
}

Josh Code

Check the colour depth settings on the computer.

If any of the computers uses 16-bit colour depth, some little changes will happen to the colours due to not being stored to the same precision.

: Hi all,
:
: I am writing a C# .net data plotting application. I use
: Graphics.DrawLine() to draw my pretty plot lines. Then in the
: MouseMove event I use a call to windows API GetPixel() (code below)
: to read the pixel under the mouse. If it is the same color as one
: of the plot lines I highlight that line next time it is drawn...
: pretty simple stuff!
:
: The problem is that this works perfectly on my home PC, but on my
: work PC there is a discrepancy between the colour of the drawn line
: and the colour I read using GetPixel(). I am not sure if the line
: is drawn with the wrong color, or the wrong color is read! Eg I
: write a colour like A=255, R=255, G=128, B= 128 and I read a colour
: like A=255, R=255, G=132, B=132. There is no problem with standard
: colours like white, red, black etc...
:
: Any help would be greatly appreciated...
:
:
: Color color = Color.Empty;
: if (control != null)
: {
: IntPtr hDC = GetDC(control.Handle);
: int colorRef = GetPixel(hDC, x, y);
: color = Color.FromArgb(
: (int)(colorRef & 0x000000FF),
: (int)(colorRef & 0x0000FF00) >> 8,
: (int)(colorRef & 0x00FF0000) >> 16);
: //color = ColorTranslator.FromWin32(colorRef);
: ReleaseDC(control.Handle, hDC);
: }
:

ashesman

So how do I programmaticly determine if the computer is running in 16 bit mode. I suppose I could limit the selection of colours to 16 bit. Without checking I am 99% sure my work PC was running in true color mode... I will look into this in a few days.

Another thought I had was to do with the drawing functions. I assume the Graphics class does some clever stuff when it draws to create softer effects. Any ideas on this?


: Check the colour depth settings on the computer.
:
: If any of the computers uses 16-bit colour depth, some little
: changes will happen to the colours due to not being stored to the
: same precision.
:
: : Hi all,
: :
: : I am writing a C# .net data plotting application. I use
: : Graphics.DrawLine() to draw my pretty plot lines. Then in the
: : MouseMove event I use a call to windows API GetPixel() (code below)
: : to read the pixel under the mouse. If it is the same color as one
: : of the plot lines I highlight that line next time it is drawn...
: : pretty simple stuff!
: :
: : The problem is that this works perfectly on my home PC, but on my
: : work PC there is a discrepancy between the colour of the drawn line
: : and the colour I read using GetPixel(). I am not sure if the line
: : is drawn with the wrong color, or the wrong color is read! Eg I
: : write a colour like A=255, R=255, G=128, B= 128 and I read a colour
: : like A=255, R=255, G=132, B=132. There is no problem with standard
: : colours like white, red, black etc...
: :
: : Any help would be greatly appreciated...
: :
: :
: : Color color = Color.Empty;
: : if (control != null)
: : {
: : IntPtr hDC = GetDC(control.Handle);
: : int colorRef = GetPixel(hDC, x, y);
: : color = Color.FromArgb(
: : (int)(colorRef & 0x000000FF),
: : (int)(colorRef & 0x0000FF00) >> 8,
: : (int)(colorRef & 0x00FF0000) >> 16);
: : //color = ColorTranslator.FromWin32(colorRef);
: : ReleaseDC(control.Handle, hDC);
: : }
: :
: