TWAIN

1. TWAIN • Open industry standard interface for the input devices to capture multimedia objects • More and more sophisticated devies are developed to cater to the needs of various applications

2. HOW THESE DEVICES ARE USED? • Applications were initially written for a single device • Eg. OCR reads a text and imports the file as ASCII file to the application. • Less flexible and so used different appl. Program for different devices. • Time consuming

3. Contd. • Later, device drivers were provided with all devices to provide an interface between program and the devices • Appl. program became more complex. • Complicated code for supporting multiple interfaces.

4. USAGE OF TWAIN • TWAIN working group created an open industry standard interface for input devices • Single TWAIN interface can be used to interface different devices.

5. BENEFITS OF TWAIN • Application developers can code a single TWAIN interface • Device manufacturers can write device drivers with TWAIN spec. • Multiple devices can be used in appl. Using “Acquire” & “Select Source”

6. OBJECTIVES • Supports multiple platform • Supports multiple devices • Widespread acceptance with std. interface • Extendibility & backward compatibility • Multidata format • Easy to use

7. TWAIN ARCHITECTURE

8. APPLICATION LAYER • Sets up a logical connection with device • No rules on the design • User interface guideline to select sources • Select source helps to select multiple sources • Acquire helps to import data from the selected device.

9. PROTOCOL LAYER • Provides interface for appl. Layer • Comm. between appl. and acquisition layer • Specifies services provided by a source • Does not specify physical connection, control & devices info. • Source Manager – heart of protocol layer

10. SOURCE MANAGER • Provide std. API for all sources • Selection of sources • Establish logical sessions b/w appl. and sources. • Regulates traffic and validate transactions • Load or unload sources • Maintain default source • Keep track of sessions and session identities

11. ACQUISTION LAYER • Contains virtual device driver • Acts directly with device driver Local SOURCE Remote

12. Functions of source • Control of device • Acquisition of data from device • Transfer of data in agreed format • Control of devices by user DEVICE LAYER Receives the s/w commands and controls the device hardware accordingly

13. New WAVE RIFF file format • Two mandatory subchunks fmt data Four optional subchunks fact cue points playlist associated data list RIFF STRUCTURE RIFF( ‘WAVE’ <‘fmt’-ck> [<fact-ck>] [<cue-ck>] [<playlist-ck>] [<assoc-data-list>] <wave-data> )

14. FACT ,CUE POINT & Playlist • Fact chunk <fact-ck>->fact(<dwSampleLength:DWORD> ) Cue–point chunk struct { DWORD dwName; DWORD dwposition; FOURCC fccChunk; DWORD dwChunkStart; DWORD dwBlockStart; DWORD dwSampleOffset; Playlist chunk Struct { DWORD dwName; DWORD dwLength; DWORD dwLoops; }

15. Associated &Inst Chunk Associated data chunk: <assoc-data-list> ->LIST( ‘adtl’ <label-ck> <note-ck> <ltxt-ck> ) Inst chunk: <instrument-ck> -> inst( <bUnshiftedNote:BYTE> <chFineTune:CHAR> <chGain:CHAR> <bLowNote:BYTE> <bHighNote:BYTE> <bLowVelocity:BYTE> <bHighVelocity:BYTE> )

16. Setting up new WAVE types • Mandatory chunks fact fmt Extended waveform structure typedef struct waveformat_extended_tag { WORD wFormatTag; WORD wChannels; DWORD nSamplesPerSec; DWORD nAvgBytesPerSec; WORD nBlockAlign; WORD wBitsPerSample; WORD cbSize; }

17. Table

18. Microsoft ADPCM WAVE file • Typedef struct adpcmoef_tag { int iCoef1; int iCoef2; } typedef struct adpcmwaveformat_tag { EXTWAVEFORMATEXT ewf; WORD nSamplesPerBlock; WORD nNumberCoef; ADPCMCOEFSET aCoeff[nNumCoef]; }ADPCMWAVEFORMAT;

19. WAVEFORMATEXT • wFormatTag WAVE_FORMAT_ADPCM • nChannels No. of channels in wave • nSamplesPerSec Frequency of the sample rate • nAvgBytesPerSec Avg. data rate • nBlockAlign block alignment of data in<data-ck> • wbitsPerSample No. of bits per sample of ADPCM • cbExtraSize size in bytes of WAVE format chunk • nSamplesPerBlock no. of samples per block • nNumCoef No. of coefficient sets in aCoef • aCoef coefficients used by wave

20. BLOCK • It has 3 parts Header, data & padding typedef struct adpcmblockheader_tag { BYTE bpredictor[nChannels]; Int iDelta[nChannels]; Int iSamp1[nChannels]; Int iSamp2[nChannels]; }ADPBLOKHEADER; CCITT Standard Companded WAVE types Stores file-dependent info about the contents of Wave data Two types OF wFormatTag WAVE_FORMAT_ALAM (0X0006) USED IN U.S WAVE_FORMAT_MULAW(OX0007) USED IN EUROPE Note: Rest as in previous slide

21. DVI ADPCM WAVE • DEFINED AS WAVE_FORMAT_DVI_ADPCM(OXOO11) • STRUCTURE typedef struct dvi_adpcmwaveformat_tag{ WAVEFORMATEXT ewf; WORD wSamplesPerBlock; }DVIADPCMWAVEFORMAT; • wFormatTag is WAVE_FORMAT_DVI_ADPCM.

22. BLOCK • Block has 2 parts • Header • Data Header Typedef struct dvi_adpcmblockheader_tag { Int iSamp0; BYTE bStepTableIndex; BYTE bReserved; }.DVI_ADPCMBLOCKHEADER;

23. Creative Labs ADPCM • Supports compression & decompression in real time • Fact Chunk : wFormatTag is WAVE_FORMAT_CREATIVE_ADPCM(0X0200) Typedef struct creative_adpcmwaveformat_tag { WAVEFORMATEXT ewf; WORD wRevision; }CREATIVEHEADPCMWAVEFORMAT; wRevision - Revision of the algorithm

24. Dolby Labs AC-2 Wave Type • Primarily used for music compression • The wFormatType of the fact chunk is WAVE_FORMAT_DOLBY_AC2(0X0030) WAVEFORMATEXT STRUCTURE: nAuxBitsCode – Auxillary bits code indicating no. of aux bits per block code no. of bits/block 0 0 1 8 2 16 3 32

25. THANK YOU