QB64 is a modern extended BASIC programming language that retains QBasic/QuickBASIC 4.5 compatibility and compiles native binaries for Windows, Linux, and macOS.

The SAVEIMAGE SUB program to create Bitmaps of other type Images or Screenshots

Bitmaps are image files with the .BMP file name extension.


The following example uses a SUB program created to save a 32 bit JPEG image as a bitmap using QB64’s graphic functions:

Module Demo Code: Change the _LOADIMAGE filename to an image file you can access.

i& = _LOADIMAGE("nice.jpg",32) ' loads a 32 bit .JPG file image
SaveImage i&, "nice"      'saves it as .BMP file "nice.bmp"
'SaveImage 0, "screenshot" 'saves entire program screen as "screenshot.bmp"

SUB SaveImage (image AS LONG, filename AS STRING)
bytesperpixel& = _PIXELSIZE(image&)
IF bytesperpixel& = 0 THEN PRINT "Text modes unsupported!": END
IF bytesperpixel& = 1 THEN bpp& = 8 ELSE bpp& = 24
x& = _WIDTH(image&)
y& = _HEIGHT(image&)
b$="BM????QB64????"+MKL$(40)+MKL$(x&)+MKL$(y&)+MKI$(1)+MKI$(bpp&)+MKL$(0)+"????"+STRING$(16, 0) 'partial BMP header info(???? to be filled later)
IF bytesperpixel& = 1 THEN
  FOR c& = 0 TO 255 ' read BGR color settings from JPG image + 1 byte spacer(CHR$(0))
    cv& = _PALETTECOLOR(c&, image&) ' color attribute to read. 
    b$ = b$ +CHR$(_BLUE32(cv&))+CHR$(_GREEN32(cv&))+CHR$(_RED32(cv&))+CHR$(0) 'spacer byte
MID$(b$, 11, 4) = MKL$(LEN(b$)) ' image pixel data offset(BMP header)
lastsource& = _SOURCE
_SOURCE image&
IF ((x& * 3) MOD 4) THEN padder$ = STRING$(4 - ((x& * 3) MOD 4), 0)
FOR py& = y& - 1 TO 0 STEP -1 ' read JPG image pixel color data 
  r$ = ""
  FOR px& = 0 TO x& - 1
   c& = POINT(px&, py&) 'POINT 32 bit values are large LONG values 
   IF bytesperpixel& = 1 THEN r$ = r$ + CHR$(c&) ELSE r$ = r$ + LEFT$(MKL$(c&), 3)
  NEXT px&  
  d$ = d$ + r$ + padder$
NEXT py&
_SOURCE lastsource&
MID$(b$, 35, 4) = MKL$(LEN(d$)) ' image size(BMP header)
b$ = b$ + d$ ' total file data bytes to create file
MID$(b$, 3, 4) = MKL$(LEN(b$)) ' size of data file(BMP header)
IF LCASE$(RIGHT$(filename$, 4)) <> ".bmp" THEN ext$ = ".bmp"
OPEN filename$ + ext$ FOR OUTPUT AS #f&: CLOSE #f& ' erases an existing file
OPEN filename$ + ext$ FOR BINARY AS #f&
PUT #f&,,b$
END SUB * *     

Code by Galleon

This SUB program can also be $INCLUDE with any program!

SUB Explanation: b$ and d$ assemble the entire string of data to create a bitmap file. Some of the bitmap header info is placed later using a MID$ (statement) to add final header numerical data converted to ASCII characters by MKI$ or MKL$.

After the header, the RGB color settings are created using ASCII characters read backwards as Blue, Green, Red and CHR$(0) as a spacer. MKL$ places the byte values in reverse order too. Bitmaps and icons require that format. LEFT$ trims off the _ALPHA byte.

The actual image is read as pixel attributes from the image bottom to the top for proper formatting with zero padding when necessary.

* Note: 32-bit images will be saved as 24-bit BMP files. All palette indexed images/modes will be saved as 256 color BMP files. Text modes cannot be saved. As QB64 has no official _SAVEIMAGE command yet and QBasic programs to save screen-shots don’t work in QB64 yet this is a very useful alternative.

See Also