Creating the printer's wire data for bi-coloured print. More...

Data Structures
struct	qlhsv
	Coloured dot for bi-colour printing in HSV. More...

struct	colour_line_wire_data
	Printer command (one part of it) to print one bi-coloured line. More...

struct	colour_line_wrapper
	Wrapper to define the command for one colour line of printer data. More...

Macros
#define	HIGH_ENERGY 0x01

#define	LOW_ENERGY 0x02

Functions
static void	overlapping_dots_remove (size_t cnt, uint8_t black_block[cnt], const uint8_t red_block[cnt])

static void	colour_line_encode (struct colour_line_wrapper *cmd, size_t input_cnt, const conv_type inputb[input_cnt], const conv_type inputr[input_cnt])

static struct colour_line_wrapper *	colour_command_get (size_t bytes_per_line)

static void	colour_command_put (void *cmd)

static int	ql_colour_line_process (struct ql8_drv t1, struct halftone_converter cnv_black, struct halftone_converter *cnv_red)

static double	fraction (double no)

static void	rgb2hsv (struct qlhsv hsv, const struct caps_dot_rgb rgb_pixel)

static void	red_dot_mark (signed int val, conv_type black_pixel, conv_type red_pixel)

static void	black_dot_mark (signed int val, conv_type black_pixel, conv_type red_pixel)

static signed int	to_grey (const struct caps_dot_rgb *pixel)

static signed int	is_red (struct ql8_drv t1, const struct caps_dot_rgb pixel)

static int	ql_next_colour_line_read (struct ql8_drv t1, struct halftone_converter cnv_black, struct halftone_converter *cnv_red)

int	ql_colour_page_print (struct ql8_drv *t1)

Detailed Description

Copyright: GNU General Public License 2.0 or later

Author: Jürgen Borleis

The QL8xx familiy of printers is capable of printing red and black dots on a special medium (e.g. DK2251).

"Colour" here means: black and red on white labels.

In this mode every line must be sent twice. First for low energie to print red dots and second for high energie to print black dots.

The result isn't perfect, since low energy creates red dots, the high energy black dots all have red shadows around them (because the high energy cools down beside the main dot area, the medium tends to red colour). Refer bi_colour_limitation for details.

Macro Definition Documentation

◆ HIGH_ENERGY

#define HIGH_ENERGY 0x01

Value to force a black dot. Used in the printer's command to print the black dots, refer colour_line_wire_data for details

◆ LOW_ENERGY

#define LOW_ENERGY 0x02

Value to force a red dot. Used in the printer's command to print the red dots, refer colour_line_wire_data for details

Function Documentation

◆ overlapping_dots_remove()

static void overlapping_dots_remove	(	size_t	cnt,
		uint8_t	black_block[cnt],
		const uint8_t	red_block[cnt]
	)

static

Remove dots in the black_block, if they are already set in the red_block

Parameters

[in]	cnt	Element count in `black_block` and `red_block`
[in,out]	black_block	Monochrome data for black dots
[in]	red_block	Monochrome data for red dots

We should not send the command for low energy and high energy at the same dot position. So, remove the black dots (high energy) in favour of the red dots (low energy) if they overlap.

Precondition: Both blocks must have the same data size

◆ colour_line_encode()

static void colour_line_encode	(	struct colour_line_wrapper *	cmd,
		size_t	input_cnt,
		const conv_type	inputb[input_cnt],
		const conv_type	inputr[input_cnt]
	)

static

Create the command to print one dual colour line

Parameters

[out]	cmd	Command data structure where to store the line data
[in]	input_cnt	Count of signed shorts in `inputb` and `inputr` (max. 2040 elements, usual 720 elements)
[in]	inputb	Black data to convert
[in]	inputr	Red data to convert

The printer wire colour data format is:

  | command | <bytes_per_line> | command | <bytes_per_line> |

e.g. according to the QL800 datasheet 186 bytes over all (two times 90 bytes per line each, plus overhead).

Precondition: Both input blocks must have the same data size

◆ colour_command_get()

static struct colour_line_wrapper * colour_command_get ( size_t bytes_per_line )

static

Allocate the buffer for the colour print command

Parameters

[in] bytes_per_line Expected bytes per line to be sent to the printer

Returns: colour_line_wrapper structure

◆ colour_command_put()

static void colour_command_put ( void * cmd )

static

Free the buffer for the colour print command

Parameters

[in] cmd The command buffer to be freed

◆ ql_colour_line_process()

static int ql_colour_line_process	(	struct ql8_drv *	t1,
		struct halftone_converter *	cnv_black,
		struct halftone_converter *	cnv_red
	)

static

Process one line and send it to the printer

Parameters

[in]	t1	Full job description
[in]	cnv_black	Black data half-tone converter
[in]	cnv_red	Red data half-tone converter

Return values

0	On success

Precondition: The half tone converters must already be filled with two lines; One of the three available half-tone algorithms must already be selected

◆ fraction()

static double fraction ( double no )

static

Return the fractional part of a floating point

Parameters

[in] no The full number

Returns: the fractional part of no

Todo:: can lrint() be used here instead?

◆ rgb2hsv()

static void rgb2hsv	(	struct qlhsv *	hsv,
		const struct caps_dot_rgb *	rgb_pixel
	)

static

Convert one pixel from RGB colour space to HSV colour space

Parameters

[out]	hsv	The target HSV colour space
[in]	rgb_pixel	The RGB pixel to convert

all three components equal to '0' will print a black dot.
all three components equal to '0xff' will print no dot.

Note: If the colour is on the vertical axis (e.g. a shade of grey), the qlhsv::hue component is returned as a negative number to mark it as invalid/undefined/do-not-use. But the qlhsv::value component is still valid in this case.

https://github.com/iamh2o/rgbw_colorspace_converter/
https://www.neltnerlabs.com/saikoled/how-to-convert-from-hsi-to-rgb-white

◆ red_dot_mark()

static void red_dot_mark	(	signed int	val,
		conv_type *	black_pixel,
		conv_type *	red_pixel
	)

static

Mark a red dot value into both line bufffers

Parameters

[in]	val	The brightness of the dot (-255 = full red brightness … 0 = no colour) (negative value!)
[out]	black_pixel	Where to store the corresponding black value for no black dot at this position
[out]	red_pixel	Where to store the corresponding red value

The input values for the red dots get inverted. A 0x00 input means "no red", so a 255 is stored to keep the paper colour. And a -255 input means a "full red", so a 0 is stored to print a red dot. At the same position, the black pixel is setup to keep the paper colour and to not disturb the red dot printing.

◆ black_dot_mark()

static void black_dot_mark	(	signed int	val,
		conv_type *	black_pixel,
		conv_type *	red_pixel
	)

static

Mark a black dot value into both line bufffers

Parameters

[in]	val	The brightness of the dot (-255 = full brightness … 0 = black) (negative value!)
[out]	black_pixel	Where to store the corresponding black value for no black dot at this position
[out]	red_pixel	Where to store the corresponding red value

The black dots scale from 0x00 (black dot!) to 0xff (paper colour!) Red settings depends on red_dot_mark() and its inversion, e.g. both colours scale from 0x00 (dot!) to 0xff (no dot!)

◆ to_grey()

static signed int to_grey ( const struct caps_dot_rgb * pixel )

static

Convert an RGB pixel to grey scale

Parameters

[in] pixel The pixel in RGB to convert (scale is 0…255 in each channel)

Returns: Grey value of the coloured RGB pixel (0…255)

Precondition: All colour component values are scaled from 0x00 … 0xff. Still expected scale here is: '0' no-colour, 0xff full colour (values for a screen, not printer)

https://duckduckgo.com/?q=color%20picker%20%23808080

◆ is_red()

static signed int is_red	(	struct ql8_drv *	t1,
		const struct caps_dot_rgb *	pixel
	)

static

Check, if the given pixel in RGB colour space defines a red pixel

Parameters

[in]	t1	Full job description
[in]	pixel	The RGB pixel to check

Return values

Positive	Black pixel brightness (grey scale value)
Negative	Red pixel brightness (hsv's value)

This is a simple and ugly red dot detection. Since we have an RGB colour space, a red colour is hard to detect. Converting it into an HSV colour space makes it simpler to detect red.
If the hue is below 30° or above 350° it is more or less a red. It then depends on its saturation and value if it is a visible red - or still a black.
All checked values are user defined and part of the ql8_drv structure.

◆ ql_next_colour_line_read()

static int ql_next_colour_line_read	(	struct ql8_drv *	t1,
		struct halftone_converter *	cnv_black,
		struct halftone_converter *	cnv_red
	)

static

Read in the next line from an RGB raster right border aligned and separate black (e.g. shades of grey) and red (shades of)

Parameters

[in]	t1	Full job description
[in,out]	cnv_black	The black part of the line
[in,out]	cnv_red	The red part of the line

Precondition: Input raster is expected as RGB 'chunked', 8 bit per channel (e.g. RGB RGB RGB …)

Todo:: The input raster can be smaller than the required line width. In this case the labels are smaller (for example) and the raster must be right aligned.

Note: Both colours gets scaled to COLOUR_VAL_DARK (dot) to COLOUR_VAL_BRIGHT (no dot) in both halftone converters

◆ ql_colour_page_print()

int ql_colour_page_print ( struct ql8_drv * t1 )

Convert the current page into the printer's wire data format

Parameters

[in] t1 Full job description

Return values

0	On success
-EINVAL	Unsupported raster input format
-ECANCELED	Termination request from outerspace

The routine loops through all or the remaining lines of the current page and converts them into the printer's colour wire format

Precondition: The format was already checked, e.g. it fits into the printer's media.

Data Structures

Macros

Functions

Detailed Description

Macro Definition Documentation

◆ HIGH_ENERGY

◆ LOW_ENERGY

Function Documentation

◆ overlapping_dots_remove()

◆ colour_line_encode()

◆ colour_command_get()

◆ colour_command_put()

◆ ql_colour_line_process()

◆ fraction()

◆ rgb2hsv()

◆ red_dot_mark()

◆ black_dot_mark()

◆ to_grey()

◆ is_red()

◆ ql_next_colour_line_read()

◆ ql_colour_page_print()