Convertire un file immagine in un altro formato immagine con le funzioni esterne del API di ImageMagick

Le risorse della libreria esterna ImageMagick consentono di convertire un file immagine in uno di questi formati: PNG, JPEG, BMP, TIFF, WebP, GIF e TGA. ^{[nota 1]}

Sarà necessario avere installata nel proprio sistema la libreria condivisa: "libMagickWand-6.Q16.so.6.0.0 ".

Mostriamo un esempio pratico, con il quale si convertirà un file immagine in un file immagine di formato WEBP:

Library "libMagickWand-6.Q16:6.0.0"

Private Const MagickPathExtent As Integer = 4096

Public Struct MagickWand
  id As Long
  name[MagickPathExtent] As Byte
  images As Pointer
  image_info As Pointer
  exception As Pointer
  insert_before As Integer
  image_pending As Integer
  debug_ As Integer
  signature As Long
End Struct

Private Enum MagickFalse = 0, MagickTrue

' void MagickWandGenesis(void)
' Initializes the MagickWand environment.
Private Extern MagickWandGenesis()

' MagickWand *NewMagickWand(void)
' Returns a wand required for all other methods in the API.
Private Extern NewMagickWand() As MagickWand

' MagickBooleanType MagickReadImage(MagickWand *wand,const char *filename)
' Reads an image or image sequence.
Private Extern MagickReadImage(wand As MagickWand, filename As String) As Integer

' MagickBooleanType MagickWriteImages(MagickWand *wand, const char *filename,const MagickBooleanType adjoin)
' Writes an image or image sequence.
Private Extern MagickWriteImages(wand As MagickWand, filename As String, adjoin As Boolean) As Integer

' MagickWand *DestroyMagickWand(MagickWand *wand)
' Deallocates memory associated with an MagickWand.
Private Extern DestroyMagickWand(wand As MagickWand) As MagickWand

' void MagickWandTerminus(void)
' Terminates the MagickWand environment.
Private Extern MagickWandTerminus()


Public Sub Form_Open()

 Dim bo As Integer
 Dim mwand As MagickWand
 Dim fileimmagine, nuovofile As String

 fileimmagine = "/percorso/del/file/da/convertire"
 nuovofile = "/tmp/immagine.webp"

 MagickWandGenesis()

 mwand = NewMagickWand()

 bo = MagickReadImage(mwand, fileimmagine)
 If bo = MagickFalse Then
   Termina(mwand)
   Error.Raise("Impossibile caricare l'immagine !")
 Endif

 bo = MagickWriteImages(mwand, nuovofile, MagickTrue)
 If bo = MagickFalse Then
   Termina(mwand)
   Error.Raise("Impossibile creare il nuovo file dell'immagine ruotata !")
 Endif

 Termina(mwand)

End


Private Procedure Termina(mw As MagickWand)    ' Libera la memoria e termina il programma

 DestroyMagickWand(mw)
 MagickWandTerminus()

End

Note

[1] Vedere questa pagina: https://products.fileformat.com/image/c/imagemagick/