VB/WinAPI/Graphics, How To Convert BMP 24 bit to BMP 8 bit in VB?

How To Convert BMP 24 bit to BMP 8 bit in VB?

Author	Message
Mike D Sutto #1 / 3	How To Convert BMP 24 bit to BMP 8 bit in VB? You can create a DC at any bit depth, after all it's just changing the number of bits it takes to store each pixel. The bit depth of the DC is determined (At least I think this is how it goes, please correct me if I'm wrong) by the bit depth of the bitmap that's selected into it. You set the bit depth of that in the BITMAPINFOHEADER structure. As long as you keep the image as a DIB then you can work at any bit depth you want, the only time you have to worry about the screen resolution is when you convert your DIB to a DDB. To save the image as an 8-Bit bitmap then you write out the DIB information to a file. First you have a BITMAPFILEHEADER type, then the BITMAPINFO type which consists of one BITMAPINFOHEADER followed by the palette as RGBQUAD type entries. Finally the image data is written (Remember to DWord align the scan lines though) out as a byte stream in the case of and 8-Bit image or packed data in the case of 1 or 4-bit images, and these simply point to a colour in the palette. Hope this helps, Mike -- EDais -- WWW: http://www.--*.com/
Mon, 07 Jul 2003 19:19:55 GMT

Alex Li #2 / 3	How To Convert BMP 24 bit to BMP 8 bit in VB? I can't understand it very well,please give me some examples,ok? Thank you! Quote: > You can create a DC at any bit depth, after all it's just changing the > number of bits it takes to store each pixel. The bit depth of the DC is > determined (At least I think this is how it goes, please correct me if I'm > wrong) by the bit depth of the bitmap that's selected into it. You set the > bit depth of that in the BITMAPINFOHEADER structure. > As long as you keep the image as a DIB then you can work at any bit depth > you want, the only time you have to worry about the screen resolution is > when you convert your DIB to a DDB. > To save the image as an 8-Bit bitmap then you write out the DIB information > to a file. > First you have a BITMAPFILEHEADER type, then the BITMAPINFO type which > consists of one BITMAPINFOHEADER followed by the palette as RGBQUAD type > entries. > Finally the image data is written (Remember to DWord align the scan lines > though) out as a byte stream in the case of and 8-Bit image or packed data > in the case of 1 or 4-bit images, and these simply point to a colour in the > palette. > Hope this helps, > Mike > -- EDais -- > WWW: Http://Members.xoom.com/EDais/
Tue, 08 Jul 2003 08:59:46 GMT

Mike D Sutto #3 / 3	How To Convert BMP 24 bit to BMP 8 bit in VB? Quote: > I can't understand it very well,please give me some examples,ok? I gave you all the information you need, for more info on DIB's have a look at the MSDN, here's an example export routine assuming your headers and such have already been filled: '* Warning: Air code 'Add the following type's from the API viewer: ' BITMAPFILEHEADER ' BITMAPINFO ' BITMAPINFOHEADER ' RGBQUAD Dim bmpFH As BITMAPFILEHEADER Dim bmpInf As BITMAPINFO Dim ImgData() As Byte Dim FNum As Integer Call WriteBmp("X:\Path\FileName.bmp") Sub WriteBmp(inFile As String) FNum = FreeFile Open inFile For Binary As #FNum Put #FNum, , bmpFH Put #FNum, , bmpInf Put #FNum, , ImgData() Close #FNum End Sub '* Hope this helps, Mike -- EDais -- WWW: Http://Members.xoom.com/EDais/
Tue, 08 Jul 2003 16:50:17 GMT

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