fpi_do_movement_estimation ()

void
fpi_do_movement_estimation (struct fpi_frame_asmbl_ctx *ctx,
                            GSList *stripes);

fpi_do_movement_estimation() estimates the movement between adjacent frames, populating delta_x and delta_y values for each fpi_frame.

This function is used for devices that don't do movement estimation in hardware. If hardware movement estimation is supported, the driver should populate delta_x and delta_y instead.

fpi_assemble_frames ()

FpImage *
fpi_assemble_frames (struct fpi_frame_asmbl_ctx *ctx,
                     GSList *stripes);

fpi_assemble_frames() assembles individual frames into a single image. It expects delta_x and delta_y of fpi_frame to be populated.

fpi_assemble_lines ()

FpImage *
fpi_assemble_lines (struct fpi_line_asmbl_ctx *ctx,
                    GSList *lines,
                    size_t num_lines);

fpi_assemble_lines assembles individual lines into a single image. It also rescales image to account variable swiping speed.

Note that num_lines might be shorter than the length of the list, if some lines should be skipped.

struct fpi_frame

struct fpi_frame {
  int           delta_x;
  int           delta_y;
  unsigned char data[0];
};

fpi_frame is used to store frames for swipe sensors. Drivers should populate delta_x and delta_y if the device supports hardware movement estimation.

struct fpi_frame_asmbl_ctx

struct fpi_frame_asmbl_ctx {
  unsigned int  frame_width;
  unsigned int  frame_height;
  unsigned int  image_width;
  unsigned char (*get_pixel)(struct fpi_frame_asmbl_ctx *ctx,
                             struct fpi_frame           *frame,
                             unsigned int                x,
                             unsigned int                y);
};

fpi_frame_asmbl_ctx is a structure holding the context for frame assembling routines.

Drivers should define their own fpi_frame_asmbl_ctx depending on hardware parameters of scanner. image_width is usually 25% wider than frame_width to take horizontal movement into account.

struct fpi_line_asmbl_ctx

struct fpi_line_asmbl_ctx {
  unsigned int line_width;
  unsigned int max_height;
  unsigned int resolution;
  unsigned int median_filter_size;
  unsigned int max_search_offset;
  int          (*get_deviation)(struct fpi_line_asmbl_ctx *ctx,
                                GSList                    *line1,
                                GSList                    *line2);
  unsigned char (*get_pixel)(struct fpi_line_asmbl_ctx *ctx,
                             GSList                    *line,
                             unsigned int               x);
};

fpi_line_asmbl_ctx is a structure holding the context for line assembling routines.

Drivers should define their own fpi_line_asmbl_ctx depending on the hardware parameters of the scanner. Swipe scanners of this type usually return two lines, the second line is often narrower than first and is used for movement estimation.

The max_search_offset value indicates how many lines forward the assembling routines should look while searching for next line. This value depends on how fast the hardware sends frames.

The function pointed to by get_deviation should return the numerical difference between two lines. Higher values means lines are more different. If the reader returns two lines at a time, this function should be used to estimate the difference between pairs of lines.