Develop Reference

Screenshot with BitBlt results in black image on Windows 10

I am using the code below to capture a screenshot of the currently active window. This code comes from Capture screenshot Including Semitransparent windows in .NET, with a few small additions, i.e. it uses GetForegroundWindow and also a timer so that I can select the desired window.
On Windows 10 (x64) this works fine for Firefox browser, but it does not work with Chrome or Edge.
I find it strange that Screenshot captured using BitBlt in C# results a black image on Windows 10 [duplicate] is marked as a duplicate, because the answer from above (first link) does not solve this problem.
Any ideas why it does not work for Chrome or Edge?
Code:
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Windows.Forms;
using System.Runtime.InteropServices;
namespace App1
{
/// <summary>
/// Description of MainForm.
/// </summary>
public partial class MainForm : Form
{
public MainForm()
{
//
// The InitializeComponent() call is required for Windows Forms designer support.
//
InitializeComponent();
//
// TODO: Add constructor code after the InitializeComponent() call.
//
}
void DoCapture()
{
label1.Text = "Capturing...";
try
{
IntPtr hDesk = GetForegroundWindow();
//IntPtr hDesk = GetDesktopWindow();
var windowRect = new RECT();
GetWindowRect(hDesk, out windowRect);
int width = (int)(windowRect.Right - windowRect.Left);
int height = (int)(windowRect.Bottom - windowRect.Top);
Size sz = new Size(width, height);
sz.Width = (int)(sz.Width * 1.25); // this is just an adjustment for the Windows zoom factor of 125%
sz.Height = (int)(sz.Height * 1.25);
IntPtr hSrce = GetWindowDC(hDesk);
IntPtr hDest = CreateCompatibleDC(hSrce);
IntPtr hBmp = CreateCompatibleBitmap(hSrce, sz.Width, sz.Height);
IntPtr hOldBmp = SelectObject(hDest, hBmp);
bool b = BitBlt(hDest, 0,0, sz.Width, sz.Height, hSrce,
0, 0, CopyPixelOperation.SourceCopy | CopyPixelOperation.CaptureBlt);
Bitmap bmp = Bitmap.FromHbitmap(hBmp);
SelectObject(hDest, hOldBmp);
DeleteObject(hBmp);
DeleteDC(hDest);
ReleaseDC(hDesk, hSrce);
bmp.Save(#"c:\temp\test.png");
bmp.Dispose();
label1.Text = "Done";
}
catch (Exception e){
label1.Text = "Exception Occurred";
textBox1.Text = e.ToString();
}
}
void Button1Click(object sender, EventArgs e)
{
timer1.Enabled = true;
}
// P/Invoke declarations
[DllImport("gdi32.dll")]
static extern bool BitBlt(IntPtr hdcDest, int xDest, int yDest, int
wDest, int hDest, IntPtr hdcSource, int xSrc, int ySrc, CopyPixelOperation rop);
[DllImport("user32.dll")]
static extern bool ReleaseDC(IntPtr hWnd, IntPtr hDc);
[DllImport("gdi32.dll")]
static extern IntPtr DeleteDC(IntPtr hDc);
[DllImport("gdi32.dll")]
static extern IntPtr DeleteObject(IntPtr hDc);
[DllImport("gdi32.dll")]
static extern IntPtr CreateCompatibleBitmap(IntPtr hdc, int nWidth, int nHeight);
[DllImport("gdi32.dll")]
static extern IntPtr CreateCompatibleDC(IntPtr hdc);
[DllImport("gdi32.dll")]
static extern IntPtr SelectObject(IntPtr hdc, IntPtr bmp);
[DllImport("user32.dll")]
public static extern IntPtr GetDesktopWindow();
[DllImport("user32.dll")]
public static extern IntPtr GetForegroundWindow();
[DllImport("user32.dll")]
public static extern IntPtr GetWindowDC(IntPtr ptr);
[DllImport("user32.dll")]
static extern bool GetWindowRect(IntPtr hWnd, out RECT lpRect);
[StructLayout(LayoutKind.Sequential)]
public struct RECT
{
public int Left; // x position of upper-left corner
public int Top; // y position of upper-left corner
public int Right; // x position of lower-right corner
public int Bottom; // y position of lower-right corner
}
void Timer1Tick(object sender, EventArgs e)
{
timer1.Enabled = false;
DoCapture();
}
}
}
Running this in SharpDevelop 5.1

Likely it doesn't work for these 2 browsers because they use a hardware-accelerated graphics context (OpenGL- or DirectX-based) to render their content, and this is incompatible with GDI-based calls.

I can suggest a simple workaround:
First use GetForegroundWindow to get the active window rect. Then call GetDesktopWindow and use that handle with the call to BitBlt:
Just add a single line to above code:
IntPtr hDesk = GetForegroundWindow();
... // get dimensions of active window
hDesk = GetDesktopWindow(); // add this line
IntPtr hSrce = GetWindowDC(hDesk);
IntPtr hDest = CreateCompatibleDC(hSrce);
Works fine.

Tessnet 2 return wrong result

I trying to run tessnet on a bitmap returned from a screenshot created with getwindow function but the result is bad. I tried to run on a bmp file saved in paint. This image is same as image created with getwindow and for this the tessnet work. This is the image Any idea?
public const int SRCCOPY = 13369376;
public const int WM_CLICK = 0x00F5;
[DllImport("user32.dll", SetLastError = true)]
internal static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
[DllImport("user32.dll", EntryPoint = "GetDC")]
internal extern static IntPtr GetDC(IntPtr hWnd);
[DllImport("gdi32.dll", EntryPoint = "CreateCompatibleDC")]
internal extern static IntPtr CreateCompatibleDC(IntPtr hdc);
[DllImport("gdi32.dll", EntryPoint = "CreateCompatibleBitmap")]
internal extern static IntPtr CreateCompatibleBitmap(IntPtr hdc, int nWidth, int nHeight);
[DllImport("gdi32.dll", EntryPoint = "DeleteDC")]
internal extern static IntPtr DeleteDC(IntPtr hDc);
[DllImport("user32.dll", EntryPoint = "ReleaseDC")]
internal extern static IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDc);
[DllImport("gdi32.dll", EntryPoint = "BitBlt")]
internal extern static bool BitBlt(IntPtr hdcDest, int xDest, int yDest, int wDest, int hDest, IntPtr hdcSource, int xSrc, int ySrc, int RasterOp);
[DllImport("gdi32.dll", EntryPoint = "SelectObject")]
internal extern static IntPtr SelectObject(IntPtr hdc, IntPtr bmp);
[DllImport("gdi32.dll", EntryPoint = "DeleteObject")]
internal extern static IntPtr DeleteObject(IntPtr hDc);
[DllImport("user32.dll")]
public static extern int SendMessage(
int hWnd, // handle to destination window
uint Msg, // message
long wParam, // first message parameter
long lParam // second message parameter
);
[StructLayout(LayoutKind.Sequential)]
public struct RECT
{
public int Left;
public int Top;
public int Right;
public int Bottom;
}
[DllImport("user32.dll", SetLastError = true)]
static extern bool GetWindowRect(IntPtr hWnd, out RECT lpRect);
public static Bitmap createBitmapFromWindow(string windowClass,string windowTitle,Point sarok1,Point sarok2)
{
IntPtr hWnd = FindWindow(windowClass, windowTitle);
Bitmap bmp = null;
IntPtr hdcFrom = GetDC(hWnd);
IntPtr hdcTo = CreateCompatibleDC(hdcFrom);
RECT windowSize;
GetWindowRect(hWnd, out windowSize);
int height = windowSize.Bottom;
int width = windowSize.Right;
IntPtr hBitmap = CreateCompatibleBitmap(hdcFrom, width, height);
if (hBitmap != IntPtr.Zero)
{
// adjust and copy
IntPtr hLocalBitmap = SelectObject(hdcTo, hBitmap);
int posx, posy;
if (sarok1.X > sarok2.X)
{
posx = sarok2.X;
}
else
{
posx = sarok1.X;
}
if (sarok1.Y > sarok2.Y)
{
posy = sarok2.Y;
}
else
{
posy = sarok1.Y;
}
BitBlt(hdcTo, 0, 0, Math.Abs(sarok1.X-sarok2.X), Math.Abs(sarok1.Y-sarok2.Y),
hdcFrom, posx, posy, SRCCOPY);
SelectObject(hdcTo, hLocalBitmap);
//We delete the memory device context.
DeleteDC(hdcTo);
//We release the screen device context.
ReleaseDC(hWnd, hdcFrom);
//Image is created by Image bitmap handle and assigned to Bitmap variable.
bmp = System.Drawing.Image.FromHbitmap(hBitmap);
DeleteObject(hBitmap);
}
return bmp;
}
public static void main()
{
Bitmap b1 = new Bitmap(createBitmapFromWindow(null, "window title", new Point(557, 460), new Point(670, 500)));
Bitmap b = b1.Clone(new Rectangle(new Point(0, 0), new Size(110, 29)),PixelFormat.Format24bppRgb);
var ocr = new Tesseract();
ocr.Init(#"path", "eng", false);
b.SetResolution(300, 300);
List<Word> l = ocr.DoOCR(b, Rectangle.Empty);
}

Tesseract expects black font on white background. An invert, a histogram equalization and a conversion to grayscale will help.
Looks like your images will consists of numbers only. You can hint tesseract to look for a numbers (and the point only). But I don't know how to do that with Tessnet.
Tesseract doesn't like different sized fonts. If the result is still not good it might be necessary to split the image in two different images and feed them separately.

Taking Screenshot of a Particular Application

I am trying to take the screenshot of a particular area (application) in the desktop. Please, check this code...
try
{
//Process p = Process.Start("notepad");
//Process p = Process.GetProcessById(11152);
if (p == null)
Console.WriteLine("Got Null");
else
{
IntPtr h = p.Handle;
SetForegroundWindow(h);
ShowWindow(h, 9);
Rect rect = new Rect();
IntPtr error = GetWindowRect(p.MainWindowHandle, ref rect);
while (error == (IntPtr)0)
{
error = GetWindowRect(p.MainWindowHandle, ref rect);
}
Thread.Sleep(2000);
int width = rect.right - rect.left;
int height = rect.bottom - rect.top;
System.IO.FileStream fs = System.IO.File.Create(#"D:\snapshot.jpg");
Bitmap bitmap = new Bitmap(width, height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
Graphics.FromImage(bitmap).CopyFromScreen(rect.left, rect.top, 0, 0, new Size(width, height), CopyPixelOperation.SourceCopy);
bitmap.Save(fs, System.Drawing.Imaging.ImageFormat.Jpeg);
fs.Close();
bitmap.Dispose();
}
}
catch (Exception ex)
{
Console.WriteLine(ex);
}
and I have this outside this method..
[DllImport("user32.dll")]
private static extern bool SetForegroundWindow(IntPtr hWnd);
[DllImport("user32.dll")]
private static extern bool IsIconic(IntPtr hWnd);
[DllImport("user32.dll")]
private static extern IntPtr GetForegroundWindow();
[DllImport("user32.dll")]
private static extern IntPtr ShowWindow(IntPtr hWnd, int nCmdShow);
[DllImport("user32.dll")]
public static extern IntPtr GetWindowRect(IntPtr hWnd, ref Rect rect);
[StructLayout(LayoutKind.Sequential)]
public struct Rect
{
public int left;
public int top;
public int right;
public int bottom;
}
When I try to open a new application and try to take screenshot (like notepad in this eg) it works like a charm. But when I try to take the screenshot of a currently running application (like task manager etc..) It does not work (I still get an image of small black rectangle).. Please help me..

Change
IntPtr h = p.Handle;
to
IntPtr h = p.MainWindowHandle;
and check.

Drawing text to a Bitmap with TextRenderer

I am trying to draw some text using TextRenderer (since this is favorable to using Graphics.DrawString) to a Bitmap, however it is having some very undesirable effects.
Example Code
using (Bitmap buffer = new Bitmap(this.ClientRectangle.Width, this.ClientRectangle.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb))
{
using (Graphics graphics = Graphics.FromImage(buffer))
{
// Produces the result below
graphics.TextRenderingHint = System.Drawing.Text.TextRenderingHint.ClearTypeGridFit;
// Produces clean text, but I'd really like ClearType!
graphics.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAliasGridFit;
TextRenderer.DrawText(graphics, "Hello World", this.Font, this.ClientRectangle, Color.Black);
}
e.Graphics.DrawImageUnscaled(buffer, this.ClientRectangle);
}
Result
I'm not sure exactly how to fix this...help!
I do NOT want to use Graphics.DrawString as I want correct GDI (as opposed to GDI+) rendering.
NOTE: I've just realized, I've left a gaping hole in this question. Some people have pointed out that rendering ClearType text is working fine on their machines...
I'm trying to render the text to a transparent (Color.Transparent) bitmap. If I do it with a solid color, everything works fine! (but it is imperative that I render to a transparent Bitmap).

Specify a BackColor in your call to DrawText():
TextRenderer.DrawText(graphics, "Hello World", this.Font, this.ClientRectangle, Color.Black, this.BackColor);

You can try setting TextRenderingHint for your Image Graphics:
using (Graphics graphics = Graphics.FromImage(buffer))
{
graphics.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAliasGridFit;
TextRenderer.DrawText(graphics, "Hello World", this.Font, this.ClientRectangle, Color.Black);
}

The issue is that TextRenderer uses GDI rendering that uses ClearType to render text, clear-type uses special anti-aliasing algorithm to smooth the text, unfortunately it doesn't work when you try to draw on bitmap device.
To make it work you have to use a trick, draw into in-memory and then copy to bitmap:
Create in-memory bitmap buffer that is compatible with display device context (IntPtr.Zero handle)
Fill the buffer background with solid color or image
Render the text into the memory bitmap
Copy from in-memory bitmap to image device context (BitBlt)
See this blog for details: GDI text rendering to image.
Sample code, sorry its a bit long:
public static class Test
{
public static Image Render()
{
// create the final image to render into
var image = new Bitmap(190, 30, PixelFormat.Format32bppArgb);
// create memory buffer from desktop handle that supports alpha channel
IntPtr dib;
var memoryHdc = CreateMemoryHdc(IntPtr.Zero, image.Width, image.Height, out dib);
try
{
// create memory buffer graphics to use for HTML rendering
using (var memoryGraphics = Graphics.FromHdc(memoryHdc))
{
// must not be transparent background
memoryGraphics.Clear(Color.White);
// execute GDI text rendering
TextRenderer.DrawText(memoryGraphics, "Test string 1", new Font("Arial", 12), new Point(5, 5), Color.Red, Color.Wheat);
TextRenderer.DrawText(memoryGraphics, "Test string 2", new Font("Arial", 12), new Point(100, 5), Color.Red);
}
// copy from memory buffer to image
using (var imageGraphics = Graphics.FromImage(image))
{
var imgHdc = imageGraphics.GetHdc();
BitBlt(imgHdc, 0, 0, image.Width, image.Height, memoryHdc, 0, 0, 0x00CC0020);
imageGraphics.ReleaseHdc(imgHdc);
}
}
finally
{
// release memory buffer
DeleteObject(dib);
DeleteDC(memoryHdc);
}
return image;
}
private static IntPtr CreateMemoryHdc(IntPtr hdc, int width, int height, out IntPtr dib)
{
// Create a memory DC so we can work off-screen
IntPtr memoryHdc = CreateCompatibleDC(hdc);
SetBkMode(memoryHdc, 1);
// Create a device-independent bitmap and select it into our DC
var info = new BitMapInfo();
info.biSize = Marshal.SizeOf(info);
info.biWidth = width;
info.biHeight = -height;
info.biPlanes = 1;
info.biBitCount = 32;
info.biCompression = 0; // BI_RGB
IntPtr ppvBits;
dib = CreateDIBSection(hdc, ref info, 0, out ppvBits, IntPtr.Zero, 0);
SelectObject(memoryHdc, dib);
return memoryHdc;
}
[DllImport("gdi32.dll")]
public static extern int SetBkMode(IntPtr hdc, int mode);
[DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
private static extern IntPtr CreateCompatibleDC(IntPtr hdc);
[DllImport("gdi32.dll")]
private static extern IntPtr CreateDIBSection(IntPtr hdc, [In] ref BitMapInfo pbmi, uint iUsage, out IntPtr ppvBits, IntPtr hSection, uint dwOffset);
[DllImport("gdi32.dll")]
public static extern int SelectObject(IntPtr hdc, IntPtr hgdiObj);
[DllImport("gdi32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool BitBlt(IntPtr hdc, int nXDest, int nYDest, int nWidth, int nHeight, IntPtr hdcSrc, int nXSrc, int nYSrc, int dwRop);
[DllImport("gdi32.dll")]
public static extern bool DeleteObject(IntPtr hObject);
[DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
public static extern bool DeleteDC(IntPtr hdc);
[StructLayout(LayoutKind.Sequential)]
internal struct BitMapInfo
{
public int biSize;
public int biWidth;
public int biHeight;
public short biPlanes;
public short biBitCount;
public int biCompression;
public int biSizeImage;
public int biXPelsPerMeter;
public int biYPelsPerMeter;
public int biClrUsed;
public int biClrImportant;
public byte bmiColors_rgbBlue;
public byte bmiColors_rgbGreen;
public byte bmiColors_rgbRed;
public byte bmiColors_rgbReserved;
}
}

c# gdi32 bitblt seems to do nothing

I'm trying to use BitBlt to get regions of a graphics and store them in bitmaps.
But here, I do something easier to understand my problem:
Bitmap sourceBitmap = new Bitmap(64, 64, PixelFormat.Format32bppRgb);
Graphics sourceGraphics = Graphics.FromImage(sourceBitmap);
Bitmap destBitmap = new Bitmap(64, 64, PixelFormat.Format32bppRgb);
Graphics destGraphics = Graphics.FromImage(destBitmap);
sourceGraphics.FillRectangle(new SolidBrush(Color.Red), new Rectangle(0, 0, 30, 30));
sourceGraphics.FillRectangle(new SolidBrush(Color.Green), new Rectangle(30, 30, 30, 30));
destGraphics.FillRectangle(new SolidBrush(Color.Blue), new Rectangle(0, 0, 30, 30));
destGraphics.FillRectangle(new SolidBrush(Color.Yellow), new Rectangle(30, 30, 30, 30));
IntPtr destDC = destGraphics.GetHdc();
IntPtr destHB = destBitmap.GetHbitmap();
IntPtr old = SelectObject(destDC, destHB);
IntPtr sourceDC = sourceGraphics.GetHdc();
IntPtr sourceHB = sourceBitmap.GetHbitmap();
old = SelectObject(sourceDC, sourceHB);
int success = BitBlt(
destDC, 0, 0, 64, 64, sourceDC, 0, 0, 0x00CC0020
);
Why after the BitBlt my destBitmap contains blue/yellow rectangles (initial bitmap in destination) instead of the red/green rectangles which should have been blitted from the source bitmap ?
Imports are done like this :
[System.Runtime.InteropServices.DllImportAttribute("gdi32.dll")]
private static extern int BitBlt(
IntPtr hdcDest, // handle to destination DC (device context)
int nXDest, // x-coord of destination upper-left corner
int nYDest, // y-coord of destination upper-left corner
int nWidth, // width of destination rectangle
int nHeight, // height of destination rectangle
IntPtr hdcSrc, // handle to source DC
int nXSrc, // x-coordinate of source upper-left corner
int nYSrc, // y-coordinate of source upper-left corner
System.Int32 dwRop // raster operation code
);
[System.Runtime.InteropServices.DllImportAttribute("gdi32.dll")]
public static extern IntPtr SelectObject(IntPtr hdc, IntPtr obj);
[System.Runtime.InteropServices.DllImportAttribute("gdi32.dll")]
public static extern void DeleteObject(IntPtr obj);
And finally cleaning code, and bitmap streaming to see bitmap content :
DeleteObject(destHB);
DeleteObject(sourceHB);
destGraphics.ReleaseHdc();
sourceGraphics.ReleaseHdc();
string path = "c:/tmp/dest.png";
destBitmap.Save(path);

Found a combination that works...but I don't understand why (definitely not a GDI expert):
I've added in calls to create compatible DCs with CreateCompatibleDC().
But note that in the actual call to BitBlt(), I'm still using the original DC "destDC" for the destination DC (not the new "destCDC"), but the new compatible DC "sourceCDC" for the source DC. No other combo seemed to work. I still, however, had to create a compatible DC for the destination even though I wasn't using it in the BitBlt() call:
private const int SRCCOPY = 0xCC0020;
[System.Runtime.InteropServices.DllImportAttribute("gdi32.dll")]
private static extern int BitBlt(
IntPtr hdcDest, // handle to destination DC (device context)
int nXDest, // x-coord of destination upper-left corner
int nYDest, // y-coord of destination upper-left corner
int nWidth, // width of destination rectangle
int nHeight, // height of destination rectangle
IntPtr hdcSrc, // handle to source DC
int nXSrc, // x-coordinate of source upper-left corner
int nYSrc, // y-coordinate of source upper-left corner
int dwRop // raster operation code
);
[System.Runtime.InteropServices.DllImportAttribute("gdi32.dll")]
public static extern IntPtr CreateCompatibleDC(IntPtr hdc);
[System.Runtime.InteropServices.DllImportAttribute("gdi32.dll")]
public static extern IntPtr SelectObject(IntPtr hdc, IntPtr obj);
[System.Runtime.InteropServices.DllImportAttribute("gdi32.dll")]
public static extern void DeleteObject(IntPtr obj);
private void button1_Click(object sender, EventArgs e)
{
Bitmap sourceBitmap = new Bitmap(64, 64, PixelFormat.Format32bppRgb);
Graphics sourceGraphics = Graphics.FromImage(sourceBitmap);
Bitmap destBitmap = new Bitmap(64, 64, PixelFormat.Format32bppRgb);
Graphics destGraphics = Graphics.FromImage(destBitmap);
sourceGraphics.FillRectangle(new SolidBrush(Color.Red), new Rectangle(0, 0, 30, 30));
sourceGraphics.FillRectangle(new SolidBrush(Color.Green), new Rectangle(30, 30, 30, 30));
destGraphics.FillRectangle(new SolidBrush(Color.Blue), new Rectangle(0, 0, 30, 30));
destGraphics.FillRectangle(new SolidBrush(Color.Yellow), new Rectangle(30, 30, 30, 30));
IntPtr destDC = destGraphics.GetHdc();
IntPtr destCDC = CreateCompatibleDC(destDC);
IntPtr destHB = destBitmap.GetHbitmap();
IntPtr oldDest = SelectObject(destCDC, destHB);
IntPtr sourceDC = sourceGraphics.GetHdc();
IntPtr sourceCDC = CreateCompatibleDC(sourceDC);
IntPtr sourceHB = sourceBitmap.GetHbitmap();
IntPtr oldSource = SelectObject(sourceCDC, sourceHB);
int success = BitBlt(
destDC, 0, 0, 64, 64, sourceCDC, 0, 0, SRCCOPY
);
SelectObject(destCDC, oldDest);
SelectObject(sourceCDC, oldSource);
DeleteObject(destCDC);
DeleteObject(sourceCDC);
DeleteObject(destHB);
DeleteObject(sourceHB);
destGraphics.ReleaseHdc();
sourceGraphics.ReleaseHdc();
pictureBox1.Image = sourceBitmap;
pictureBox2.Image = destBitmap;
}
Anyone have any insight as to why this combo works?...