Eseguire una scansione e riconoscimento caratteri (OCR) con l'API di Sane, Tesseract e Leptonica
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Versione del 8 giu 2024 alle 12:55 di Vuott (Discussione | contributi)
Usando le risorse esterne del API di Sane, Tesseract e Leptonica è possibile eseguire una scansione con la Scanner e il successivo riconoscimento caratteri (OCR) di un documento testuale.
In particolare con le funzioni esterne della libreria libsane si eseguirà la scansione attraverso uno scanner; con le funzioni esterne della libreria liblept si caricherà l'immagine ottenuta dalla scansione del documento, e con le funzioni esterne della libreria libtesseract si eseguirà il riconoscimento ottico dei caratteri presenti nell'immagine caricata.
E' necessario avere installate nel sistema e richiamare in Gambas le seguenti librerie condivise:
"libsane.so.1.3.1 ", "libtesseract.so.5.0.3 " e "liblept.so.5.0.4 "
Mostriamo un esempio pratico:
Private Const BUFFER As Integer = 65536 Private Const MODUS As String = "Color" ' Color - Gray - Lineart Private RISOLUZIONE As Integer = 300 Private Const OCR_BOOL As Boolean = True Library "libsane:1.3.1" Public Struct SANE_Option_Descriptor name As Pointer title As Pointer desc As Pointer type As Integer unit As Integer size As Integer cap As Integer constraint_type As Integer union As Pointer End Struct Public Struct SANE_Parameters sformat As Integer last_frame As Integer bytes_per_line As Integer pixels_per_line As Integer lines As Integer depth As Integer End Struct Private Enum SANE_ACTION_GET_VALUE = 0, SANE_ACTION_SET_VALUE, SANE_ACTION_SET_AUTO ' SANE_Status sane_init (SANE_Int * version_code, SANE_Auth_Callback authorize) ' This function must be called before any other SANE function can be called. Private Extern sane_init(version_code As Pointer, authorize As Pointer) As Integer ' SANE_Status sane_get_devices (const SANE_Device *** device_list, SANE_Bool local_only) ' To query the list of devices that are available. Private Extern sane_get_devices(device_list As Pointer, local_only As Boolean) As Integer ' SANE_Status sane_open (SANE_String_Const devicename, SANE_Handle * handle) ' To establish a connection to a particular device. Private Extern sane_open(devicename As String, handle As Pointer) As Integer ' SANE_Status sane_control_option (SANE_Handle handle, SANE_Int option, SANE_Action action, void *value, SANE_Int * info) ' To set or inquire the current value of option number n of the device represented by handle h. Private Extern sane_control_option(handle As Pointer, option As Integer, action As Integer, value As Pointer, info As Pointer) As Integer ' const SANE_Option_Descriptor * sane_get_option_descriptor (SANE_Handle handle, SANE_Int option) ' To access option descriptors. Private Extern sane_get_option_descriptor(handle As Pointer, option As Integer) As Pointer ' SANE_Status sane_get_parameters (SANE_Handle handle, SANE_Parameters * params) ' To obtain the current scan parameters. Private Extern sane_get_parameters(handle As Pointer, params As SANE_Parameters) As Integer ' SANE_Status sane_start (SANE_Handle handle) ' Initiates aquisition of an image from the device represented by handle h. Private Extern sane_start(handle As Pointer) As Integer ' SANE_Status sane_read (SANE_Handle handle, SANE_Byte * data, SANE_Int max_length, SANE_Int * length) ' Reads image data from the device represented by handle h. Private Extern sane_read(handle As Pointer, data As Pointer, max_length As Integer, length As Pointer) As Integer ' void sane_cancel (SANE_Handle handle) ' Cancels the currently pending operation of the device. Private Extern sane_cancel(handle As Pointer) ' void sane_close (SANE_Handle h) ' Terminates the association between the device handle passed in argument h and the device it represents. Private Extern sane_close(h As Pointer) ' void sane_exit (void) ' To terminate use of a backend. Private Extern sane_exit() Public Sub Main() Dim i, n, maxlun, lun As Integer Dim dev, hnd, md, buf, plun As Pointer Dim nom As String Dim sod As SANE_Option_Descriptor Dim par As New SANE_Parameters Dim fl As File Write "\e[5mRestare in attesa...\e[0m" Flush i = sane_init(0, 0) If i > 0 Then GestErrore("sane_init()") i = sane_get_devices(VarPtr(dev), False) If i > 0 Then GestErrore("sane_get_devices()") While Pointer@(dev + i) > 0 nom = String@(Pointer@(Pointer@(dev + i))) i += 8 Wend Write "\rDispositivo: \e[31m" & nom i = sane_open(nom, VarPtr(hnd)) If i > 0 Then GestErrore("sane_open()") saneUscita(hnd) Endif i = sane_control_option(hnd, 0, SANE_ACTION_GET_VALUE, VarPtr(n), 0) If i > 0 Then GestErrore("sane_control_option()") saneUscita(hnd) Endif Print "\n\n\e[0mPossibili opzioni:\e[32m" For i = 0 To n - 1 sod = sane_get_option_descriptor(hnd, i) If IsNull(String@(sod.name)) Then Continue Print " " & String@(sod.name) Select Case String@(sod.name) Case "mode" ' Color - Gray - Lineart md = Alloc(MODUS) sane_control_option(hnd, i, SANE_ACTION_SET_VALUE, md, 0) Case "resolution" sane_control_option(hnd, i, SANE_ACTION_SET_VALUE, VarPtr(RISOLUZIONE), 0) End Select Next i = sane_get_parameters(hnd, par) If i > 0 Then GestErrore("sane_get_parameters()") saneUscita(hnd) Endif With par Dim px As Byte = .bytes_per_line / .pixels_per_line Dim rgb As String = " byte)" If px == 3 Then rgb = " byte = RGB)" Print "\n\e[0mColonne: "; .pixels_per_line; " (1 colonna = 1 pixel = "; px; RGB Print "Righe: "; .lines Print "Byte per riga: "; .bytes_per_line; " (colonne x "; px; Left(rgb, 5); ")" Print "Bit per campione: "; .depth Print "Modalità: "; MODUS Print "Risoluzione: "; RISOLUZIONE; " dpi\n" End With i = sane_start(hnd) If i > 0 Then GestErrore(hnd, "sane_start()") saneUscita(hnd) Endif buf = Alloc(SizeOf(gb.Byte), BUFFER) plun = Alloc(SizeOf(gb.Integer), 1) maxlun = BUFFER fl = Open "/tmp/imm" For Create Repeat i = sane_read(hnd, buf, maxlun, plun) Select Case i Case 1 GestErrore("sane_read()") saneUscita(hnd) Case 3 To 4 GestErrore("sane_read()") saneUscita(hnd) Case 6 To 11 GestErrore("sane_read()") saneUscita(hnd) End Select lun = Int@(plun) Write #fl, buf, lun Until lun = 0 CreaFileImmagine(par) ' Libera la memoria precedentemente allocata: fl.Close Free(md) Free(plun) Free(buf) saneUscita(hnd) ' Chiama la funzione per il riconoscimento OCR: If OCR_BOOL = True Then Ocr() End Private Procedure GestErrore(fnz As String) Error.Raise("Errore alla funzione: " & fnz) End Private Procedure saneUscita(handle As Pointer) sane_cancel(handle) sane_close(handle) sane_exit() End Private Procedure CreaFileImmagine(prmt As SANE_Parameters) Dim s, finale, mg As String Dim pro, p4, colonne, righe As Integer Dim bBN As Byte pro = prmt.lines * prmt.bytes_per_line s = File.Load("/tmp/imm") Print "Dati grezzi: "; Len(s); " byte (Colonne x Righe x 3 byte_RGB)" colonne = prmt.pixels_per_line righe = prmt.lines Select Case MODUS Case "Color" mg = "P6 " ' Se il numero dei dati grezzi è inferiore a (Colonne x Righe) x 3, allora colma la differenza: If Len(s) < ((pro / 8) * 3) Then s = s & String(((pro) * 3) - Len(s), Chr(255)) ' Se invece il numero dei dati grezzi è maggiore di (Colonne x Righe) x 3, allora colma la differenza, ma tagliando i dati grezzi dalla fine: If Len(s) > ((pro) * 3) Then s = Left(s, pro * 3) Case "Gray" mg = "P5 " ' Se il numero dei dati grezzi è inferiore a Colonne x Righe, allora colma la differenza: If Len(s) < (pro) Then s = s & String((pro) - Len(s), Chr(255)) ' Se invece il numero dei dati grezzi è maggiore di Colonne x Righe, allora colma la differenza, ma tagliando i dati grezzi dalla fine: If Len(s) > (pro) Then s = Left(s, pro) Case "Lineart" mg = "P4 " ' Se il numero dei dati grezzi è inferiore a (Colonne x Righe) / 8, allora colma la differenza: If Len(s) < (pro / 8) Then p4 = pro \ 8 s = s & String$(p4 - Len(s), Chr(255)) Endif ' Se il numero dei dati grezzi è maggiore di (Colonne x Righe) / 8, allora colma la differenza: If Len(s) > (pro / 8) Then For bBN = 1 To 8 If (Len(s) * 8) Mod (prmt.lines + bBN) == 0 colonne = prmt.lines + bBN righe = Len(s) * 8 / prmt.lines Endif Next Endif End Select ' Quindi, crea l'intero file .PNM finale, costituito da: ' l'header: ' - numero Magico + spazio; ' - numero colonne; ' - spazio; ' - numero righe; ' - spazio; ' - profondità colore; ' - chiusura con "salto di riga"; ' i dati grezzi dell'immagine scansita; ' le informazioni e commento finale: finale = mg & CStr(colonne) & Chr(&20) & CStr(righe) & " 255" & Chr(10) & s & Chr(10) & "# file creato da " & Application.Name & " - " & CStr(Now) ' ...e lo salva: File.Save("/tmp/scansione.pnm", finale) End Public Struct Pix w As Integer h As Integer d As Integer wpl As Integer refcount As Integer xres As Integer yres As Integer informat As Integer text As Pointer colormap As Pointer data As Pointer End Struct Library "libtesseract:5.0.3" ' TessBaseAPI* TessBaseAPICreate() Private Extern TessBaseAPICreate() As Pointer ' int TessBaseAPIInit3(TessBaseAPI* handle, const char* datapath, const char* language) Private Extern TessBaseAPIInit3(handle As Pointer, datapath As String, language As String) As Integer ' void TessBaseAPISetImage2(TessBaseAPI* handle, struct Pix* pix) Private Extern TessBaseAPISetImage2(handle As Pointer, pix As Pix) ' void TessBaseAPISetSourceResolution(TessBaseAPI* handle, int ppi) Private Extern TessBaseAPISetSourceResolution(handle As Pointer, ppi As Integer) ' int TessBaseAPIRecognize(TessBaseAPI* handle, ETEXT_DESC* monitor) Private Extern TessBaseAPIRecognize(handle As Pointer, monitor As Pointer) As Integer ' char* TessBaseAPIGetUTF8Text(TessBaseAPI* handle) Private Extern TessBaseAPIGetUTF8Text(handle As Pointer) As String ' void TessBaseAPIEnd(TessBaseAPI* handle) Private Extern TessBaseAPIEnd(handle As Pointer) ' void TessBaseAPIDelete(TessBaseAPI* handle) Private Extern TessBaseAPIDelete(handle As Pointer) Library "liblept:5.0.4" ' PIX * pixRead (const char *filename) Private Extern pixRead(filename As String) As Pix ' void pixDestroy (PIX **ppix) Private Extern pixDestroy(ppix As Pointer) Private Procedure Ocr() Dim err As Integer Dim tes, p As Pointer Dim pis As Pix Dim s As String pis = pixRead("/tmp/scansione.pnm") tes = TessBaseAPICreate() If tes == 0 Then Error.Raise("Errore !") err = TessBaseAPIInit3(tes, Null, "eng") If err <> 0 Then Error.Raise("Errore !") TessBaseAPISetImage2(tes, pis) Write "Riconoscimento caratteri.\n\e[5m Restare in attesa...\e[0m\r" Flush TessBaseAPISetSourceResolution(tes, RISOLUZIONE) err = TessBaseAPIRecognize(tes, 0) If err <> 0 Then Error.Raise("Errore !") ' Scansione OCR: s = TessBaseAPIGetUTF8Text(tes) Print Space(Len(" Restare in attesa...")) Print Print s TessBaseAPIEnd(tes) TessBaseAPIDelete(tes) pixDestroy(Object.Address(pis) + (SizeOf(gb.Pointer) * 3)) End