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For storage of Y:U:V image data (MacroSystem)

                                 FORM YUVN
                               developed by:
                  MS MacroSystem Computer GmbH (Germany)
                              Henning Friedl

The IFF-format YUVN is designed to store YUV-pictures which mainly are used
in  broadcast  television.   YUVN  supports CCIR-601-2 which is a worldwide
standard for PAL- and NTSC-television.

Chunk 'YCHD'

The  required property 'YCHD' holds a header which describes the dimensions
of  the  image and some other information which are necessary to understand
the data in the following data-chunks.  The chunk 'YCHD' must appear before
the first data-chunk ('DATY').

You will find all definitions of this chunk in the file 'yuvn.i'.


Explanations on the components of the chunk 'YCHD':


ychd_Width  indicates  the  width of the stored image.  Using YUV_MODE_411,
the width must be a multiple of four, usind YUV_MODE_422 or YUV_MODE_211 it
must  be a multiple of two!  Using YUV_MODE_444, YUV_MODE_400, YUV_MODE_222
or YUV_MODE_200 width may be any value.

The  number  of U- and V-pixels per line depends on the used YUV_MODE.  See
the table below for details.

            Mode             |    Y-pixels    |    U-pixels    |    V-pixels
YCHD_MODE_400, YCHD_MODE_200 | ychd_Width     |       -        |       -
YCHD_MODE_411                | ychd_Width (4) | ychd_Width / 4 | ychd_Width / 4
YCHD_MODE_422, YCHD_MODE_211 | ychd_Width (2) | ychd_Width / 2 | ychd_Width / 2
YCHD_MODE_444, YCHD_MODE_222 | ychd_Width     |   ychd_Width   |   ychd_Width

(2) means, in this mode ychd_Width MUST be a multiple of two!
(4) means, in this mode ychd_Width MUST be a multiple of four!


ychd_Height  indicates  the  height  (number  of  rows) of the image.  If a
full-frame picture is stored, ychd_Height must be a multiple of two!

ychd_PageWidth, ychd_PageHeight

These  fields describe the dimensions of the source page.  The image itself
can  be  smaller  or  larger.   If  not  used,  set  this to ychd_Width and

ychd_LeftEdge, ychd_TopEdge

These  fields  indicate  the  desired  position  of  this  image within the
destination picture.  If not used, set to 0,0.

ychd_xAspect, ychd_yAspect

The aspect ratio of a single pixel in the stored image.  If you do not know
the correct values (you should know them) use the following:

PAL-nonlace:   22/44           NTSC-nonlace:  22/52
PAL-lace:      22/22           NTSC-lace:     22/26

See also: 'Finding the Aspect Ratio' by Carolyn Scheppner (AmigaMail 9/10-91)


Type of compression.  0, if none.


Different  Flags.  Currently only bit-0 (YCHDB_LACE) is defined.  It should
be  set if the stored image has been a full-frame image within an interlace
video-source (TV, VTR, ...).


The type of YUV-format.  If you only want to save the luminance information
(black-and-white)   set  ychd_Mode  to  YCHD_MODE_400.   If  you  save  the
additional color-difference-signals U and V set ychd_Mode to YCHD_MODE_411,
YCHD_MODE_422  or  YCHD_MODE_444  depending  what  format you want to save.
With lores-pictures use YCHD_MODE_200, YCHD_MODE_211 or YCHD_MODE_222.


Information  on  the TV-system you got this picture from.  If you really do
not  know  set ychd_Norm to YCHD_NORM_UNKNOWN.  The better way is to set it
to the correct value YCHD_NORM_PAL or YCHD_NORM_NTSC!


The data-chunks DATY, DATU and DATV

In  the  IFF-file the chunks DATY, DATU and DATV must appear in this order.
The optional chunks DATU and DATV are both needed in color-pictures.

The data-chunk DATY

The  chunk  DATY  contains the luminance-data (Y) of the YUV-picture.  Each
pixel  is stored in one byte (8 bits), the values follow the CCIR-standard.
Y  ranges  from  16 (black) to 235 (white).  Isolated pixels may go lightly
beyond the limits but 0 and 255 must not appear!

The number of pixels in one line is given in ychd_Width.  One line directly
follows  the  other,  there  are  no  pad-bytes  between  two lines even if
ychd_Width  is odd.  Only at the end of the chunk a pad-byte ($00) might be
inserted according the IFF guidelines.

Within  a  full-frame- (interlaced-) picture the lines are ordered as if it
was  a  non-lace  picture  (first line, first frame then first line, second
frame  then second line first frame, ...).  This is the same in IFF-ILBM or
the order of the bitmaps in Amiga-memory.

The data-chunks DATU and DATV

The   chunks   DATU   and  DATV  are  optional,  they  have  to  appear  in
color-pictures because they contain the color-difference-signals.

Each  pixel  is  stored  in  one  byte  (8  bits),  the  values  follow the
CCIR-standard.   The  values  range  from  16  to  240  (128 means 0).  For
calculations you have to subtract 128 so U or V are in a range from -112 to
112  where  0  means  no  color.  Isolated pixels may go lightly beyond the
limits but 0 and 255 must not appear!



               IFND      YUVN_I
YUVN_I         SET       1
             IFND        EXEC_TYPES_I
               INCLUDE   "exec/types.i"
;---- ID's used in FORM YUVN

ID_YUVN:       equ       'YUVN'             ;the FORM-ID
ID_YCHD:       equ       'YCHD'             ;the header-chunk-ID
ID_DATY:       equ       'DATY'             ;the Y-data-chunk-ID
ID_DATU:       equ       'DATU'             ;the U-data-chunk-ID
ID_DATV:       equ       'DATV'             ;the V-data-chunk-ID

;---- values for ychd_Compress

COMPRESS_NONE  equ       0                  ;no comression

;---- values for ychd_Flags

YCHDB_LACE     equ       0                  ;if set the data-chunks contain
YCHDF_LACE     equ       1                  ;a full-frame (interlaced) picture

;---- values for ychd_Mode

YCHD_MODE_400     equ    0       ;a black-and-white picture (no DATU and DATV)
YCHD_MODE_411     equ    1       ;a YUV-411 picture
YCHD_MODE_422     equ    2       ;a YUV-422 picture
YCHD_MODE_444     equ    3       ;a YUV-444 picture

YCHD_MODE_200     equ    8       ;a lores black-and-white picture
YCHD_MODE_211     equ    9       ;a lores color picture (422, but lores)
YCHD_MODE_222     equ    10      ;a lores color picture (444, but lores)

YCHD_MODEB_LORES  equ    3       ;test this bit to check for lores/hires

;---- values for ychd_Norm

YCHD_NORM_UNKNOWN equ    0       ;unknown, try to avoid this
YCHD_NORM_PAL     equ    1       ;PAL 4.433 MHz
YCHD_NORM_NTSC    equ    2       ;NTSC 3.579 MHz

;---- the FORM-YUVN DataHeader: 'YCHD'


               UWORD     ychd_Width        ;picture width in Y-pixels
               UWORD     ychd_Height       ;picture height (rows)

               UWORD     ychd_PageWidth    ;source page width & height,
               UWORD     ychd_PageHeight   ;  normally same as Width and Height

               UWORD     ychd_LeftEdge     ;position within the source page,
               UWORD     ychd_TopEdge      ;  normally 0,0

               UBYTE     ychd_AspectX      ;pixel aspect (width : height)
               UBYTE     ychd_AspectY      ;
               UBYTE     ychd_Compress     ;(see above)
               UBYTE     ychd_Flags        ;(see above)

               UBYTE     ychd_Mode         ;(see above)
               UBYTE     ychd_Norm         ;(see above)

               WORD      ychd_reserved2    ;must be 0

               LONG      ychd_reserved3    ;must be 0

               LABEL     ychd_SIZEOF
; Warning, the UBYTE fields are byte-packed, C-compilers should not add pad
; bytes!

               ENDC      ; YUVN_I