Question How to make a bitmap from memory

[keb1965]

I have a bitmap that is being extracted piecemeal from another file where it has been stored. I can successfully read and iterpret the data and write it out to a file that can be edited/viewed/previewed etc. However, this is not the direction I would like to go.

I already have the entire file in a char() buffer that I write out to a file, but I would prefer to simply put that information directly into a PictureBox or other image control.

    Private Shared Sub bmpWriteFile(ByVal FileName As String, _
         ByRef charHeader As Byte(), _
         ByRef charBuff As Byte())

        Dim fs As IO.FileStream = New IO.FileStream(FileName, IO.FileMode.Create, IO.FileAccess.Write)
        Dim bw As IO.BinaryWriter = New IO.BinaryWriter(fs)
        bw.Seek(0, IO.SeekOrigin.Begin)
        bw.Write(charHeader)
        bw.Write(charBuff)
        bw.Close()
        fs.Close()
    End Sub

Just an FYI, I have to create the header on the fly since it is stripped from the bitmap in the source file .. that is why I write it seperately.

What I am currently doing is saving the file, then reading it into a new bitmap and assigning it to the control. If I could get away from the saving to file step it would be great!

        bmpWriteFile("C:\Temp.bmp", charHEADERBuffer, charBMPBuffer)
        Dim bmp As New Bitmap("C:\Temp.bmp")
        Me.PictureBox1.Image = bmp

Any help would be appreciated.

 

[keb1965]

Nevermind ..... I have figured out a workaround

Dim bmp As New Bitmap(bmpHeader.biWidth, bmpHeader.biHeight)
...
'loop through each pixel in the char buffer getting each color
'and put it in the pixel where it belongs
bmp.SetPixel(locX, locY, color)

 

[JohnH]

A lot faster should be to load the "file" bytes into a MemoryStream and load Image.FromStream.

 

[keb1965]

nope .. tried it and it didn't work ... invalid format .. the byte stream is not a complete bitmap ... it is merely the pixel data, no color palette and no header information ... I suppose I could put the header, pallette and pixel data into a single stream, but then I would just have to add more overhead.

Besides, it is fast enough anyway, considering the largest bitmap it will ever have to deal with is 200x200 w/256 colors

 

[JohnH]

By "file" bytes I meant the same stuff you put in the file and loaded to Bitmap, it's no different than that, only saving the disk operations.

 

[keb1965]

Ah ... I understand ... the problem is I would have 2 different streams, since the bitmap header doesn't exist in the data read from the source. I would have to recreate it and put it into the stream from the data source ...

As it is now, I only have the width and height information and the pixel data .. the source doesn't maintain the 256 color palette or the 40 byte header .. so I would have to create the header data and color palette and then inject that into the byte array of pixel data ... when I was writing it to file, I merely created a default header with the standard 256 color palette and wrote it before the pixel data.

 

[JohnH]

You would only have one MemoryStream that you Write(charHeader) and Write(charBuff) to, same as with your bmpWriteFile/FileStream code.

There is also the Bitmap Constructor (Int32, Int32, Int32, PixelFormat, IntPtr) (System.Drawing) but it can be awkward to use.