Here's the link of a UTMAG article that covers the TIFF subject deeply:
TIFF and the new GdiPlusX classes
At the topic "Extracting frames from TIFFS" you'll find the code below, that saves the frames of a TIFF in separate image files:
** HOWTO: Extract frames from a Multiframe TIFF
DO LOCFILE("System,prg")
WITH _SCREEN.System.Drawing
* Load the multiframe TIFF to GDI+
LOCAL loMultif AS xfcBitmap
loMultif = .Bitmap.New(GETPICT("TIF"))
LOCAL lnFrames, n, lcFrameFileName
lnFrames = loMultif.GetFrameCount()
IF lnFrames > 1
FOR n = 0 TO lnFrames - 1
loMultif.SelectActiveFrame(.Imaging.FrameDimension.Page, n)
lcFrameFileName = "c:\Frame" + TRANSFORM(n + 1) + ".Tif"
loMultif.Save(lcFrameFileName, .Imaging.ImageFormat.Bmp)
ENDFOR
ELSE
MESSAGEBOX("The selected file is not a Multiframe TIFF")
ENDIF
ENDWITH
RETURN