Ottenere dati grezzi di un file immagine mediante le funzioni del API di GDK-PixBuf
Da Gambas-it.org - Wikipedia.
Versione del 19 nov 2021 alle 20:59 di Vuott (Discussione | contributi)
GDK-PixBuf è una libreria grafica per il caricamento e la manipolazione delle immagini.
Alcune sue funzioni ci consentono di ottenere un Puntatore ai dati grezzi dei file immagine, e così di poterli estrarre.
Sarà necessario avere installata nel sistema la libreria: "libgdk_pixbuf-2.0.so.0.4000.0 "
Mostriamo un semplice esempio pratico:
Library "libgdk_pixbuf-2.0:0.4000.0" ' GdkPixbuf * gdk_pixbuf_new_from_file (const char *filename, GError **error) ' Creates a new pixbuf by loading an image from a file. Private Extern gdk_pixbuf_new_from_file(filename As String, GError As Pointer) As Pointer ' guchar * gdk_pixbuf_get_pixels (const GdkPixbuf *pixbuf) ' Queries a pointer to the pixel data of a pixbuf. Private Extern gdk_pixbuf_get_pixels(GdkPixbuf As Pointer) As Pointer ' int gdk_pixbuf_get_width (const GdkPixbuf *pixbuf) ' Queries the width of a pixbuf. Private Extern gdk_pixbuf_get_width(GdkPixbuf As Pointer) As Integer ' int gdk_pixbuf_get_height (const GdkPixbuf *pixbuf) ' Queries the height of a pixbuf. Private Extern gdk_pixbuf_get_height(GdkPixbuf As Pointer) As Integer ' int gdk_pixbuf_get_n_channels (const GdkPixbuf *pixbuf) ' Queries the number of channels of a pixbuf. Private Extern gdk_pixbuf_get_n_channels(GdkPixbuf As Pointer) As Integer ' gboolean gdk_pixbuf_get_has_alpha (const GdkPixbuf *pixbuf) ' Queries whether a pixbuf has an alpha channel (opacity information). Private Extern gdk_pixbuf_get_has_alpha(GdkPixbuf As Pointer) As Boolean ' void g_object_unref (gpointer object) ' Decreases the reference count of object. Private Extern g_object_unref(gobject As Pointer) Public Sub Main() Dim nomefile As String Dim w, h, i, n As Integer Dim pixbuf, dati As Pointer Dim b As Byte Dim bo As Boolean Dim st As Stream nomeFile = "/percorso/del/file/immagine" pixbuf = gdk_pixbuf_new_from_file(nomefile, 0) If pixbuf == 0 Then Error.Raise("Errore !") Print "File immagine: "; nomeFile w = gdk_pixbuf_get_width(pixbuf) Print "Larghezza: "; w; " pixel" h = gdk_pixbuf_get_height(pixbuf) Print "Altezza: "; h; " pixel" i = gdk_pixbuf_get_n_channels(pixbuf) Print "Canali: "; i bo = gdk_pixbuf_get_has_alpha(pixbuf) Print "Canale Alfa: "; bo dati = gdk_pixbuf_get_pixels(pixbuf) If dati == 0 Then Error.Raise("Errore !") ' Dereferenziamo il Puntatore con i "Memory Stream", e ne leggiamo i valori contenuti (i dati/byte grezzi dei pixel) dell'immagine: st = Memory dati For Read For n = 0 To (w * h * i) - 1 Read #st, b Print n, Hex(b) Next st.Close g_object_unref(pixbuf) End
In quest'altro esempio caricata un'immagine, utilizzando le risorse di Gambas, ed infine i dati ottenuti dei pixel saranno riutilizzati ricreando una nuova immagine identica all'immagine originaria:
Library "libgdk_pixbuf-2.0:0.4000.0" ' GdkPixbufLoader * gdk_pixbuf_loader_new(void) ' Creates a new pixbuf loader object. Private Extern gdk_pixbuf_loader_new() As Pointer ' gboolean gdk_pixbuf_loader_write (GdkPixbufLoader *loader, const guchar *buf, gsize count, GError **error) ' Cause a pixbuf loader to parse the next count bytes of an image. Private Extern gdk_pixbuf_loader_write(lo As Pointer, buf As Pointer, i As Integer, po As Pointer) ' gboolean gdk_pixbuf_loader_close (GdkPixbufLoader *loader, GError **error) ' Informs a pixbuf loader that no further writes. Private Extern gdk_pixbuf_loader_close(lo As Pointer, po As Pointer) ' GdkPixbuf * gdk_pixbuf_loader_get_pixbuf (GdkPixbufLoader *loader) ' Queries the GdkPixbuf that a pixbuf loader is currently creating. Private Extern gdk_pixbuf_loader_get_pixbuf(lo As Pointer) As Pointer ' guchar * gdk_pixbuf_get_pixels (const GdkPixbuf *pixbuf) ' Queries a pointer to the pixel data of a pixbuf. Private Extern gdk_pixbuf_get_pixels(GdkPixbuf As Pointer) As Pointer ' int gdk_pixbuf_get_width (const GdkPixbuf *pixbuf) ' Queries the width of a pixbuf. Private Extern gdk_pixbuf_get_width(GdkPixbuf As Pointer) As Integer ' int gdk_pixbuf_get_height (const GdkPixbuf *pixbuf) ' Queries the height of a pixbuf. Private Extern gdk_pixbuf_get_height(GdkPixbuf As Pointer) As Integer ' int gdk_pixbuf_get_n_channels (const GdkPixbuf *pixbuf) ' Queries the number of channels of a pixbuf. Private Extern gdk_pixbuf_get_n_channels(GdkPixbuf As Pointer) As Integer ' gboolean gdk_pixbuf_get_has_alpha (const GdkPixbuf *pixbuf) ' Queries whether a pixbuf has an alpha channel (opacity information). Private Extern gdk_pixbuf_get_has_alpha(GdkPixbuf As Pointer) As Boolean ' void g_object_unref (gpointer object) ' Decreases the reference count of object. Private Extern g_object_unref(gobject As Pointer) Public Sub Form_Open() Dim fl As File Dim bb As Byte[] Dim w, h, i As Integer Dim loader, pixbuf, dati As Pointer Dim bo As Boolean Dim st As Stream Dim imago As Image fl = Open "/percorso/del/file/immagine" For Read With bb = New Byte[Lof(fl)] .Read(fl, 0, bb.Count) End With fl.Close loader = gdk_pixbuf_loader_new() If loader == 0 Then Error.Raise("Errore !") gdk_pixbuf_loader_write(loader, bb.data, bb.count, 0) gdk_pixbuf_loader_close(loader, 0) pixbuf = gdk_pixbuf_loader_get_pixbuf(loader) If pixbuf == 0 Then Error.Raise("Errore !") w = gdk_pixbuf_get_width(pixbuf) Print "Larghezza: "; w; " pixel" h = gdk_pixbuf_get_height(pixbuf) Print "Altezza: "; h; " pixel" i = gdk_pixbuf_get_n_channels(pixbuf) Print "Canali: "; i bo = gdk_pixbuf_get_has_alpha(pixbuf) Print "Canale Alfa: "; bo dati = gdk_pixbuf_get_pixels(pixbuf) If dati == 0 Then Error.Raise("Impossibile ottenere un 'Puntatore' ai dati dei pixel dell'immagine !") ' Carichiamo i dati nel vettore "bb[]" per gestire successivamente i dati grezzi dei pixel: st = Memory dati For Read With bb = New Byte[w * h * i] .Read(st, 0, .count) End With st.Close ' Viene preparata la variabile di tipo immagine per la gestione dei dati del futuro nuovo file immagine: With imago = New Image(w, h, 0, Image.Standard) st = Memory .Data For Write End With ' Scrive i dati presenti nel vettore "bb[]" nella varibile di tipo "Image": bb.Write(st, 0, bb.Count) st.Close g_object_unref(pixbuf) PictureBox1.Image = imago imago.Save("/tmp/imago.png", 100) End