[RESOLVED] How to reproduce image using GetBitmapBits vs SetBitmapBits

[Jim Davis]

Hello!

I'm stuck here, i see no reason why i cant properly declare a dc and/or a bitmap object for a b/g/r image data i got from getbitmapbits() api.

In my theory, this should copy the image from picturebox1 to picturebox2, by converting the picture from picbox1 to a byte array, then reproduces it in a memory bitmap, that i bitblt to the picbox2.

Private Type BITMAP
    bmType As Long
    bmWidth As Long
    bmHeight As Long
    bmWidthBytes As Long
    bmPlanes As Integer
    bmBitsPixel As Integer
    bmBits As Long
End Type

Private Declare Function DeleteObject Lib "GDI32.dll" (ByVal hObject As Long) As Long
Private Declare Function SelectObject Lib "GDI32.dll" (ByVal hDC As Long, ByVal hObject As Long) As Long

Private Declare Function CreateCompatibleDC Lib "gdi32" (ByVal hDC As Long) As Long
Private Declare Function CreateCompatibleBitmap Lib "gdi32" _
    (ByVal hDC As Long, ByVal nWidth As Long, ByVal nHeight As Long) As Long
Private Declare Function BitBlt Lib "gdi32" (ByVal hDestDC As Long, ByVal X As Long, ByVal Y As Long, _
ByVal nWidth As Long, ByVal nHeight As Long, ByVal hSrcDC As Long, _
ByVal xSrc As Long, ByVal ySrc As Long, ByVal dwRop As Long) As Long

Private Sub Command1_Click()
Dim PicArray() As Byte, PicInfo As BITMAP
Dim hDC As Long, hBMP As Long, hOldBmp As Long

  GetObject Picture1.Picture, Len(PicInfo), PicInfo
  ReDim PicArray((PicInfo.bmWidth * PicInfo.bmHeight * (PicInfo.bmBitsPixel / 8)) - 1) As Byte
  GetBitmapBits Picture1.Picture, UBound(PicArray), PicArray(0)
  
  hDC = CreateCompatibleDC(Picture2.hDC)
  hBMP = CreateCompatibleBitmap(Picture2.hDC, PicInfo.bmWidth, PicInfo.bmHeight)
  
  hOldBmp = SelectObject(hDC, hBMP)
  
  Debug.Print SetBitmapBits(hBMP, UBound(PicArray), PicArray(0))
  
  Picture2.Cls
  Debug.Print BitBlt(Picture2.hDC, 0, 0, PicInfo.bmWidth, PicInfo.bmHeight, hDC, 0, 0, vbSrcCopy)
  
  SelectObject hDC, hOldBmp
  DeleteObject hBMP
  DeleteObject hDC
End Sub

What i am getting is looks horrible.

I checked the array to see, what is the array is containing, by using the setpixel. It seems to be the getbitmapbits runs fine, the problem should be around the dc and bitmap creations, but i have no idea why.

Dim PicArray() As Byte, PicInfo As BITMAP
Dim hDC As Long, hBMP As Long, hOldBmp As Long
Dim X As Long, Y As Long

  GetObject Picture1.Picture, Len(PicInfo), PicInfo
  ReDim PicArray((PicInfo.bmWidth * PicInfo.bmHeight * (PicInfo.bmBitsPixel / 8)) - 1) As Byte
  GetBitmapBits Picture1.Picture, UBound(PicArray), PicArray(0)
  Picture2.Cls
  
  For X = 0 To PicInfo.bmWidth * (PicInfo.bmBitsPixel / 8) Step (PicInfo.bmBitsPixel / 8)
    For Y = 0 To PicInfo.bmHeight - 2
      SetPixel Picture2.hDC, X / 3, Y, RGB(PicArray(Y * ((PicInfo.bmWidth * 3) + 1) + X + 2), PicArray(Y * ((PicInfo.bmWidth * 3) + 1) + X + 1), PicArray(Y * ((PicInfo.bmWidth * 3) + 1) + X + 0))
    Next
  Next

[Milk]

Two small points and a big one

When calculating the size of a buffer to hold a bitmap you must account for potential scanline padding. Each scanline must always align to a DWord, if the Width * PixelSize is not a multiple of 4 then padding bytes are added. This is not an issue with 32bpp images which always align... Ub = .bmHeight * (.bmWidth * .bmBitsPixel + 31& And -32&) \ 8 - 1

Seeing as you are using the bitmap structure you can use .bmWidthBytes instead... Ub = .bmWidthbytes * .bmHeight -1

With the calls you are using for Get/SetBitmapBits you are passing the count wrong, it should be... UBound(PicArray) + 1

The main reason why it might not work is because CreateCompatibleBitmap is most likely creating a different colour depth bitmap from the one you are trying to set to it. The kind of bitmap it creates is determined by the current desktop colour depth, on my system it creates a 32bpp bitmap. Instead of Get/SetBitmapBits you could try Get/SetDiBits, these let you specify what kind of bitmap you want.

[Jim Davis]

By using the Get/SetDiBits i got it to work. Thanks for the details, that was i missed!

Private Declare Function GetDIBits Lib "GDI32.dll" ( _
    ByVal hDC As Long, ByVal hBitmap As Long, ByVal nStartScan As Long, _
    ByVal nNumScans As Long, ByRef lpBits As Any, _
    ByRef lpBI As BitmapInfo, ByVal wUsage As Long) As Long
Private Declare Function SetDIBits Lib "GDI32.dll" ( _
    ByVal hDC As Long, ByVal hBitmap As Long, ByVal nStartScan As Long, _
    ByVal nNumScans As Long, ByRef lpBits As Any, _
    ByRef lpBI As BitmapInfo, ByVal wUsage As Long) As Long
 
 Private Type BitmapInfoHeader ' 40 bytes
    biSize As Long
    biWidth As Long
    biHeight As Long
    biPlanes As Integer
    biBitCount As Integer
    biCompression As Long
    biSizeImage As Long
    biXPelsPerMeter As Long
    biYPelsPerMeter As Long
    biClrUsed As Long
    biClrImportant As Long
End Type
 
Private Type BitmapInfo
    bmiHeader As BitmapInfoHeader
    bmiColors(255) As Long
End Type
 
Private Const DIB_RGB_COLORS As Long = 0 ' Colour table in RGBs
 
Private Sub Command2_Click()
Dim DIBInf As BitmapInfo, hDC As Long, hBMP As Long
 
  ' Set the header size
  DIBInf.bmiHeader.biSize = Len(DIBInf.bmiHeader)
  
  hDC = Picture1.hDC
  hBMP = Picture1.Picture.Handle
    
  ' Fill the header structure with information about the Bitmap
  If (GetDIBits(hDC, hBMP, 0, 0, ByVal 0&, DIBInf, DIB_RGB_COLORS)) Then
      ReDim BMData(DIBInf.bmiHeader.biSizeImage - 1) As Byte
      Call GetDIBits(hDC, hBMP, 0, DIBInf.bmiHeader.biHeight, _
          BMData(0), DIBInf, DIB_RGB_COLORS)
  
      hDC = Picture2.hDC
      hBMP = Picture2.Image.Handle
      
      Call SetDIBits(hDC, hBMP, 0, DIBInf.bmiHeader.biHeight, _
          BMData(0), DIBInf, DIB_RGB_COLORS)
  End If
 
End Sub

[Bumbling Intern]

Hi,

I'm trying to do a similar project. I am working in VB.Net 2008 express. I am trying to update a image capture / databasing program that uses VFW and make it compatible with a new USB DirectShow mircoscope. I need to be able to capture a bitmap of a live webcam. To get the image to show up in the preview window I am using Jarno Burger's webcam code found here http://www.codeproject.com/KB/audio-...ctShowNET.aspx

The only sample code for GetBitmapBIts I could find was in C so I wanted to try to play around with your code to get the screen capture of the webcam. At the moment the errors coming up say that " Picture is not a member of ' System.Windows.Forms.PictureBox' " as well as SetBitMapBits is not declared.
My ultimate goal is to be able to save the image to a folder on the hard drive where it is added to a database.
I'm still very new to VB and was hoping you might be able to post the rest of your code so I could see how it starts and try to understand what is going on.

Thanks,
Steve

[Milk]

Hi there, it's VB6 code not Vb.Net

I would also recommend not using Get/SetBitmapBits, I believe they are just there for backwards compatibility.

I think VB.Net equivalents of GetDiBits & SetDiBitsToDevice are...
System.Drawing.Bitmap.LockBits
System.Drawing.Graphics.DrawImage

[Bumbling Intern]

I chose to use GetBitMapBits because my only other option seems to be SampleGrabber. From what I have read SampleGrapher is more complex and MediaDet::GetBitMapBits will work just as well for what I need it to do.

Thanks for the reply, much appreciated

[Milk]

I'm pretty sure your best bet is System.Drawing.Bitmap.LockBits.
GetBitMapBits only still exists for the sake old 16 bit programs. GetDiBits is easier to use and more powerful.

[Ben321]

nevermind, this comment was in error