Color of a screen pixel

Color of a screen pixel
You are encouraged to solve this task according to the task description, using any language you may know.

Get color information from an arbitrary pixel on the screen, such as the current location of the mouse cursor. The mouse cursor may or may not have to be active in a GUI created by your program. These functions are OS related.

Applesoft BASIC

Low-Resolution (Lo-Res) graphics 40x48, 16 colors, page 1

X =  PDL (0) * 5 / 32
Y =  PDL (1) * 3 / 16
 COLOR=  SCRN( X,Y)

Hi-Resolution (Hi-Res) graphics 280x192, 6 colors

There is no HSCRN( X,Y) function in Applesoft. What follows is an elaborate subroutine that determines the hi-res color at location given by variables X and Y on the current hi-res page. A color value in the range from 0 to 7 is returned in the variable C. The color is determined by peeking at adjacent pixels and the MSB. The VTAB routine is used as an aid to calculate the address of pixels. Other colors beyond the 6 hi-res colors can be displayed by positioning pixels at byte boundaries using the MSB. This routine is limited to the eight hi-res colors.

 
 100  REM GET HCOLOR
 110  REM  PARAMETERS: X Y
 120  REM  RETURNS: C
 130  REM 
 140 P = 0:X = X + 1
 150  ON (X < 280) GOSUB 300
 160 PR = P:P = 0:X = X - 2
 170  ON (X >  = 0) GOSUB 300
 180 PL = P:X = X + 1: GOSUB 300
 190 ODD = X -  INT (X / 2) * 2
 200 C = H * 4
 210  IF  NOT ((PL = PR) AND (PL <  > P)) THEN C = C + P * 3: RETURN
 220  IF ODD THEN P =  NOT P
 230 C = C + P + 1
 240  RETURN 
 250  REM 
 260  REM GET PIXEL
 270  REM  PARAMETERS: X Y
 280  REM  RETURNS: H P
 290  REM 
 300 H =  INT (X / 7)
 310 V =  INT (Y / 8)
 320 VO =  PEEK (37)
 330 HO =  PEEK (36)
 340  VTAB V + 1: HTAB 1
 350 A =  PEEK (41) * 256
 360 A = A +  PEEK (40) + H
 370  VTAB VO + 1: HTAB HO + 1
 380 A = A + 8192 - 1024
 390 P =  PEEK (230) / 32
 400  IF P = 2 THEN A = A + 8192
 410 A = A + (Y - V * 8) * 1024
 420 B = X - H * 7
 430 V =  PEEK (A)
 440 H =  INT (V / 128)
 450 V =  INT (V / (2 ^ B))
 460 P = V -  INT (V / 2) * 2
 470  RETURN
 
X = 267 : Y =  166 : GOSUB 100
HCOLOR=  C
 

AutoHotkey

PixelGetColor, color, %X%, %Y%

AutoIt

$a = Mousegetpos()
PixelGetColor($a[0], $a[1])

BASIC

Works with: QuickBasic version 4.5

In a graphics mode (for instance, SCREEN 13 or SCREEN 12)

color = POINT(x, y)

BBC BASIC

In BBC BASIC for Windows you can read either the 'logical colour' (palette index) or the 'true colour' (24-bit RGB value).

      palette_index% = POINT(x%, y%)
      RGB24b_colour% = TINT(x%, y%)

C

Library: Xlib

 
#include <X11/Xlib.h>
void
get_pixel_color (Display *d, int x, int y, XColor *color)
{
  XImage *image;
  image = XGetImage (d, RootWindow (d, DefaultScreen (d)), x, y, 1, 1, AllPlanes, XYPixmap);
  color->pixel = XGetPixel (image, 0, 0);
  XFree (image);
  XQueryColor (d, DefaultColormap(d, DefaultScreen (d)), color);
}
 
// Your code
XColor c;
get_pixel_color (display, 30, 40, &c);
printf ("%d %d %d\n", c.red, c.green, c.blue);
 

Works with: Windows

(Linux users, see grabc.)

#include <Windows.h>
 
COLORREF getColorAtCursor(void) {
    POINT p;
    COLORREF color;
    HDC hDC;
    BOOL b;
 
    /* Get the device context for the screen */
    hDC = GetDC(NULL);
    if (hDC == NULL)
        return CLR_INVALID;
 
    /* Get the current cursor position */
    b = GetCursorPos(&p);
    if (!b)
        return CLR_INVALID;
 
    /* Retrieve the color at that position */
    color = GetPixel(hDC, p.x, p.y);
 
    /* Release the device context again */
    ReleaseDC(GetDesktopWindow(), hDC);
 
    return color;
}

C#

using System;
using System.Drawing;
using System.Windows.Forms;
 
class Program
{
    static Color GetPixel(Point position)
    {
        using (var bitmap = new Bitmap(1, 1))
        {
            using (var graphics = Graphics.FromImage(bitmap))
            {
                graphics.CopyFromScreen(position, new Point(0, 0), new Size(1, 1));
            }
            return bitmap.GetPixel(0, 0);
        }
    }
 
    static void Main()
    {
        Console.WriteLine(GetPixel(Cursor.Position));
    }
}

Sample output:

Color [A=255, R=243, G=242, B=231]

Clojure

(defn get-color-at [x y]
  (.getPixelColor (java.awt.Robot.) x y))

Delphi

 
program ScreenPixel;
 
{$APPTYPE CONSOLE}
 
uses
  Windows,
  SysUtils,
  Graphics;
 
 
// Use this function in a GUI application to return the color
function GetPixelColourAsColor(const PixelCoords: TPoint): TColor;
var
  dc: HDC;
begin
  // Get Device Context of windows desktop
  dc := GetDC(0);
  // Read the color of the pixel at the given coordinates
  Result := GetPixel(dc,PixelCoords.X,PixelCoords.Y);
end;
 
// Use this function to get a string representation of the current colour
function GetPixelColourAsString(const PixelCoords: TPoint): string;
var
  r,g,b: Byte;
  col: TColor;
begin
  col := GetPixelColourAsColor(PixelCoords);
 
  // Convert the Delphi TColor value to it's RGB components
  r := col and $FF;
  g := (col shr 8) and $FF;
  b := (col shr 16) and $FF;
 
  // Format the result
  Result := 'R('+IntToStr(r)+') G('+IntToStr(g)+') G('+IntToStr(b)+')';
 
  {
    Alternatively, format the result as follows to get a
    string representation of the Delphi TColor value
 
    Result := ColorToString(GetPixel(dc,curP.X,curP.Y));
  }
 
end;
 
var
  s: string;
  P: TPoint;
begin
  s := '';
 
  Writeln('Move mouse over a pixel. Hit return to get colour of selected pixel.');
 
  repeat
    Readln(s);
    if s = '' then
      begin
        GetCursorPos(P);
        Writeln('Colour at cursor position X:'+
                IntToStr(P.X)+' Y:'+
                IntToStr(P.Y) +' = '+
                GetPixelColourAsString(P)
                );
        Writeln('');
        Writeln('Move mouse and hit enter again.');
      end;
  until
    SameText(s,'quit');
 
end.
 

Example output:

Move mouse over a pixel. Hit return to get colour of selected pixel.

Colour at cursor position X:429 Y:161 = R(0) G(0) B(0)

Move mouse and hit enter again.

Colour at cursor position X:942 Y:358 = R(182) G(206) B(231)

Move mouse and hit enter again.

Colour at cursor position X:704 Y:103 = R(240) G(240) B(240)

Move mouse and hit enter again.

Colour at cursor position X:2756 Y:59 = R(250) G(196) B(182)

F#

open System.Drawing
open System.Windows.Forms
 
let GetPixel x y =
    use img = new Bitmap(1,1)
    use g = Graphics.FromImage(img)
    g.CopyFromScreen(new Point(x,y), new Point(0,0), new Size(1,1))
    let clr = img.GetPixel(0,0)
    (clr.R, clr.G, clr.B)
 
let GetPixelAtMouse () =
    let pt = Cursor.Position
    GetPixel pt.X pt.Y

C++/CLI

 
using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;
 
[STAThreadAttribute]
int main()
{
	Point^ MousePoint = gcnew Point();
	Control^ TempControl = gcnew Control();
	MousePoint = TempControl->MousePosition;
	Bitmap^ TempBitmap = gcnew Bitmap(1,1);
	Graphics^ g = Graphics::FromImage(TempBitmap);	
	g->CopyFromScreen((Point)MousePoint, Point(0, 0), Size(1, 1));
	Color color = TempBitmap->GetPixel(0,0);
	Console::WriteLine("R: "+color.R.ToString());
	Console::WriteLine("G: "+color.G.ToString());
	Console::WriteLine("B: "+color.B.ToString());
}
 

Integer BASIC

See Applesoft BASIC.

Icon and Unicon

Icon and Unicon don't have direct access to the screen; however, we can read the colour of of a maximal sized window instead. The graphics procedure generates all pixels from a rectangular selection as a comma separated string with RGB values.

link graphics,printf
 
procedure main()  
 
   WOpen("canvas=hidden")                   # hide for query
   height := WAttrib("displayheight") - 45  # adjust for ...
   width  := WAttrib("displaywidth") - 20   # ... window 7 borders
   WClose(&window)
 
   W := WOpen("size="||width||","||height,"bg=black") | 
        stop("Unable to open window")   
 
   every 1 to 10 do {   # generate some random rectangles within the frame
      x := ?width 
      y := ?(height-100)
      WAttrib("fg="||?["red","green","blue","purple","yellow"])
      FillRectangle(x,x+50,y,y+50)
      }
 
   while Event() do       
      printf("x=%d,y=%d pixel=%s\n",&x,&y,Pixel(&x,&y,&x,&y))
 
   WDone(W)                                  # q to exit
end
 

Library: Icon Programming Library

graphics.icn provides graphics printf.icn provides printf

Sample Output:

x=943,y=946 pixel=0,0,65535
x=658,y=610 pixel=47802,0,65535
x=934,y=487 pixel=0,0,0

Java

Uses: Robot

public static Color getColorAt(int x, int y){
   return new Robot().getPixelColor(x, y);
}

Liberty BASIC

'This example requires the Windows API
Struct point, x As long, y As long
 
hDC = GetDC(0)
result = GetCursorPos()
Print GetPixel(hDC, point.x.struct, point.y.struct)
Call ReleaseDC 0, hDC
End
 
 
    Sub ReleaseDC hWnd, hDC
        CallDLL #user32,"ReleaseDC", hWnd As uLong, hDC As uLong, ret As Long
    End Sub
 
    Function GetDC(hWnd)
        CallDLL #user32, "GetDC", hWnd As uLong, GetDC As uLong
    End Function
 
    Function GetCursorPos()
        CallDLL #user32, "GetCursorPos", point As struct, GetCursorPos As uLong
    End Function
 
    Function GetPixel(hDC, x, y)
        CallDLL #gdi32, "GetPixel", hDC As uLong, x As long, y As long, GetPixel As long
    End Function

Locomotive Basic

10 x=320:y=200
20 color=TEST(x,y)
30 PRINT "Pen color at"; x; y; "is"; color

Logo

CLEARSCREEN
SHOW PIXEL
[255 255 255]

PHP

Works with: PHP version 5.2.2

Works with: Windows

Library: GD

$img = imagegrabscreen();
$color = imagecolorat($im, 10, 50);
imagedestroy($im);

PicoLisp

Using 'grabc' as recommended in the C solution

(in '(grabc)
   (mapcar hex (cdr (line NIL 1 2 2 2))) )

Output:

73,61,205
-> (73 61 205)

PureBasic

Return the color used at the x,y position in the current output. If the current output has an alpha channel then the result will be a 32bit RGBA value, otherwise it will be a 24bit RGB value. The color can be split in their RGB and alpha values by using the Red(), Green(), Blue() and Alpha() functions.

Color = Point(x, y)

To get the colour of a pixel on the screen when it is not managed by PureBasic (ie. from other programs' windows), it is necessary to use Windows API. This works only under Windows.

 
hDC = GetDC_(0)
Color = GetPixel_(hDC, x, y)
ReleaseDC_(0, hDC)

This work fine!!

poz.point
If OpenWindow(0,0,0,100,45,"Get pixel color at cursor position",#PB_Window_MinimizeGadget)
  TextGadget(0,0,0,50,12,"Red: ")
  TextGadget(1,0,15,50,12,"Green: ")
  TextGadget(2,0,30,50,12,"Blue: ")
  TextGadget(3,50,0,50,12,"")
  TextGadget(4,50,15,50,12,"")
  TextGadget(5,50,30,50,12,"")
 hDC = GetDC_(0)
 Repeat
  oldx=poz\x
  oldy=poz\y
GetCursorPos_(@poz)
Color = GetPixel_(hDC, poz\x, poz\y)
If poz\x<>oldx Or poz\y<>oldy
  SetGadgetText(3,Str(Red(color)))
  SetGadgetText(4,Str(Green(color)))
  SetGadgetText(5,Str(Blue(color)))
EndIf
event=WaitWindowEvent(200)
Until event=#PB_Event_CloseWindow
ReleaseDC_(0, hDC)
EndIf

Python

Library: PyWin32

def get_pixel_colour(i_x, i_y):
	import win32gui
	i_desktop_window_id = win32gui.GetDesktopWindow()
	i_desktop_window_dc = win32gui.GetWindowDC(i_desktop_window_id)
	long_colour = win32gui.GetPixel(i_desktop_window_dc, i_x, i_y)
	i_colour = int(long_colour)
	return (i_colour & 0xff), ((i_colour >> 8) & 0xff), ((i_colour >> 16) & 0xff)
 
print get_pixel_colour(0, 0)

Library: PIL

Works with: Windows

only

def get_pixel_colour(i_x, i_y):
	import PIL.ImageGrab
	return PIL.ImageGrab.grab().load()[i_x, i_y]
 
print get_pixel_colour(0, 0)

Library: PIL

Library: python-xlib

def get_pixel_colour(i_x, i_y):
	import PIL.Image # python-imaging
	import PIL.ImageStat # python-imaging
	import Xlib.display # python-xlib
	o_x_root = Xlib.display.Display().screen().root
	o_x_image = o_x_root.get_image(i_x, i_y, 1, 1, Xlib.X.ZPixmap, 0xffffffff)
	o_pil_image_rgb = PIL.Image.fromstring("RGB", (1, 1), o_x_image.data, "raw", "BGRX")
	lf_colour = PIL.ImageStat.Stat(o_pil_image_rgb).mean
	return tuple(map(int, lf_colour))
 
print get_pixel_colour(0, 0)

Library: PyGTK

def get_pixel_colour(i_x, i_y):
	import gtk # python-gtk2
	o_gdk_pixbuf = gtk.gdk.Pixbuf(gtk.gdk.COLORSPACE_RGB, False, 8, 1, 1)
	o_gdk_pixbuf.get_from_drawable(gtk.gdk.get_default_root_window(), gtk.gdk.colormap_get_system(), i_x, i_y, 0, 0, 1, 1)
	return tuple(o_gdk_pixbuf.get_pixels_array().tolist()[0][0])
 
print get_pixel_colour(0, 0)

Library: PyQt

def get_pixel_colour(i_x, i_y):
	import PyQt4.QtGui # python-qt4
	app = PyQt4.QtGui.QApplication([])
	long_qdesktop_id = PyQt4.QtGui.QApplication.desktop().winId()
	long_colour = PyQt4.QtGui.QPixmap.grabWindow(long_qdesktop_id, i_x, i_y, 1, 1).toImage().pixel(0, 0)
	i_colour = int(long_colour)
	return ((i_colour >> 16) & 0xff), ((i_colour >> 8) & 0xff), (i_colour & 0xff)
 
print get_pixel_colour(0, 0)

Tcl

Library: Tk

Works only on X11 or OSX with Xquartz.

package require Tcl 8.5
package require Tk
 
# Farm out grabbing the screen to an external program.
# If it was just for a Tk window, we'd use the tkimg library instead
proc grabScreen {image} {
    set pipe [open {|xwd -root -silent | convert xwd:- ppm:-} rb]
    $image put [read $pipe]
    close $pipe
}
# Get the RGB data for a particular pixel (global coords)
proc getPixelAtPoint {x y} {
    set buffer [image create photo]
    grabScreen $buffer
    set data [$image get $x $y]
    image delete $buffer
    return $data
}
 
# Demo...
puts [format "pixel at mouse: (%d,%d,%d)" \
    {*}[getPixelAtPoint {*}[winfo pointerxy .]]]

TI-89 BASIC

Only the graph screen can be read.

pxlTest(y, x)              © returns boolean

Visual Basic .NET

  Private Function GetPixelColor(ByVal Location As Point) As Color
 
    Dim b As New Bitmap(1, 1)
    Dim g As Graphics = Graphics.FromImage(b)
 
    g.CopyFromScreen(Location, Point.Empty, New Size(1, 1))
 
    Return b.GetPixel(0, 0)
 
  End Function

XPL0

Color gets either 1, 2, 4, 8, 15, 16, or 24 significant bits depending on the current graphic mode enabled on an IBM-PC compatible machine with VESA graphics.

code ReadPix=44;
int  Color, X, Y;
Color:= ReadPix(X, Y);