SCGetDataTypes(3) Impressario SCGetDataTypes(3)NAMESCGetDataTypes - determine the data types supported by a scanner
SYNOPSIS
#include <stdio.h>
#include <scanner.h>
int SCGetDataTypes(SCANNER *s, SCDATATYPE **dt, int *ntypes);
DESCRIPTIONSCGetDataTypes sets *dt to point to an array of the data types supported
by the scanner driver. *ntypes gets the number of data types pointed to
by *dt. s specifies a connection to a scanner driver obtained from a
call to SCOpen(3), SCOpenFile(3), or SCOpenScreen(3).
SCDATATYPE is defined in <scanner.h> as follows:
typedef struct tag_scdatatype {
unsigned int packing : 4;
unsigned int channels : 4;
unsigned int type : 8;
unsigned int bpp : 8;
} SCDATATYPE;
packing indicates how the data for each pixel is laid out. Its value
will be one of SC_PACKPIX, SC_PACKBAND, or SC_PACKPLANE, which are
defined in <scanner.h>. If packing is SC_PACKPIX, then all the data for
each pixel is together. If packing is SC_PACKBAND then the data is
banded by row, and if packing is SC_PACKPLANE then the data is laid out
in planes (see below).
channels is the number of channels of data for this type. Black and
white data (SC_MONO, SC_GREY) consists of one channel, while color data
consists of three (SC_RGB, SC_CMY) or four (SC_CMYK).
type is used to interpret the channels of data. type should be one of
SC_MONO, SC_GREY, SC_RGB, SC_CMY, or SC_CMYK, which are defined in
<scanner.h>.
bpp is the number of bits per pixel in each channel. Thus, for
monochrome data, there is 1 bit per pixel, and for 24 bit RGB color,
there are 8 bits per pixel (* 3 channels == 24 bits).
SCDATATYPE Illustration
Suppose type is SC_RGB, and bpp is 8. In this case channels must be 3
(because type is SC_RGB), and the data is 24 bit per pixel color data.
Further suppose that our image data consists of 4 rows of 4 pixels each.
In the illustrations that follow, an R represents one byte of red data, a
G represents one byte of green data, and a B represents one byte of blue
data. The value of packing affects the layout of the image data as
Page 1
SCGetDataTypes(3) Impressario SCGetDataTypes(3)
folows:
packing == SC_PACKPIX
In this case, the pixel values for each channel will be together in each
row.
RGBRGBRGBRGB
RGBRGBRGBRGB
RGBRGBRGBRGB
RGBRGBRGBRGB
packing == SC_BANDED
In this case, the red, green and blue channels of pixel data will be
separated by row.
RRRR
GGGG
BBBB
RRRR
GGGG
BBBB
RRRR
GGGG
BBBB
RRRR
GGGG
BBBB
packing == SC_PACKPLANE
All the red data for the entire image is first, followed by all the green
data, followed by all the blue data.
RRRR
RRRR
RRRR
RRRR
RRRR
GGGG
GGGG
GGGG
GGGG
BBBB
BBBB
BBBB
BBBB
BBBB
Page 2
SCGetDataTypes(3) Impressario SCGetDataTypes(3)
Data Type Conventions
Scanner applications need not be written to support all possible data
types. There are four basic data types that are typically used:
Monochrome:
packing == SC_PACKPIX
channels == 1
type == SC_MONO
bpp == 1
ALL scanner drivers MUST support Monochrome format.
8 Bit Greyscale:
packing == SC_PACKPIX
channels == 1
type == SC_GREY
bpp == 8
All scanner drivers that support any kind of greyscale or color output
MUST support 8 Bit Greyscale format.
For color output, there are two possible situations when dealing with
well-behaved scanner drivers. One is that the red, green, and blue
channels are scanned in three seperate passes; in this case, the data
type is:
Planar 24 bit RGB color:
packing == SC_PACKPLANE
channels == 3
type == SC_RGB
bpp == 8
The other situation is a one-pass color scanner that gets all of the data
in one pass. The data type for color data from this kind of scanner is:
Packed 24 bit RGB color:
packing == SC_PACKPIX
channels == 3
type == SC_RGB
bpp == 8
A scanning application that is prepared to deal with these four data
types should be able to interact well with any well-behaved scanner
driver.
For information on setting the data type for scanning, see SCSetup(3).
Page 3
SCGetDataTypes(3) Impressario SCGetDataTypes(3)RETURN VALUESCGetDataTypes returns 0 if successful. If an error occurs, -1 is
returned and SCerrno is set to indicate the reason for failure.
EXECUTION ERROR CODESSCGetDataTypes will fail under the following circumstances.
SCEDEV Scanner driver error
SCECOMM Error communicating with scanner driver
WARNING
The memory pointed to by *dt after a call to SCGetDataTypes belongs to
libscan(3) and should not be modified by the calling program. Nor should
any assumptions be made about its values after subsequent calls to
SCGetDataTypes; in other words, it should be copied to memory owned by
the calling program before future calls to SCGetDataTypes.
SEE ALSOlibscan(3), SCOpen(3), SCSetup(3).
Page 4
