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photo(n)		     Tk Built-In Commands		      photo(n)

______________________________________________________________________________

NAME
       photo - Full-color images

SYNOPSIS
       image create photo ?name? ?options?
_________________________________________________________________

DESCRIPTION
       A  photo is an image whose pixels can display any color or be transpar-
       ent.  A photo image is stored internally in full	 color	(32  bits  per
       pixel),	and is displayed using dithering if necessary.	Image data for
       a photo image can be obtained from a file or a string,  or  it  can  be
       supplied	 from C code through a procedural interface.  At present, only
       GIF and PPM/PGM formats are supported, but an interface exists to allow
       additional  image  file	formats	 to be added easily.  A photo image is
       transparent in regions where no image data has been supplied  or	 where |
       it has been set transparent by the transparency set subcommand.

CREATING PHOTOS
       Like  all  images,  photos  are created using the image create command.
       Photos support the following options:

       -data string
	      Specifies the contents of the image as a string.	The string can
	      contain  base64  encoded data or binary data.  The format of the
	      string must be one of those for which there  is  an  image  file
	      format  handler that will accept string data.  If both the -data
	      and -file options are specified, the -file option	 takes	prece-
	      dence.

       -format format-name
	      Specifies	 the  name  of	the file format for the data specified
	      with the -data or -file option.

       -file name
	      name gives the name of a file that is to be read to supply  data
	      for  the	photo image.  The file format must be one of those for
	      which there is an image file format handler that can read	 data.

       -gamma value
	      Specifies that the colors allocated for displaying this image in
	      a window should be corrected for a non-linear display  with  the
	      specified gamma exponent value.  (The intensity produced by most
	      CRT displays is a power function of the input value, to  a  good
	      approximation; gamma is the exponent and is typically around 2).
	      The value specified must be  greater  than  zero.	  The  default
	      value  is	 one (no correction).  In general, values greater than
	      one will make the image lighter, and values less than  one  will
	      make it darker.

       -height number
	      Specifies	 the  height  of the image, in pixels.	This option is
	      useful primarily in situations where the user wishes to build up
	      the  contents of the image piece by piece.  A value of zero (the
	      default) allows the image to expand or shrink vertically to  fit
	      the data stored in it.

       -palette palette-spec
	      Specifies	 the  resolution of the color cube to be allocated for
	      displaying this image, and thus the number of colors  used  from
	      the  colormaps  of  the  windows	where  it  is  displayed.  The
	      palette-spec string may be either a single decimal number, spec-
	      ifying  the  number  of  shades of gray to use, or three decimal
	      numbers separated by  slashes  (/),  specifying  the  number  of
	      shades  of  red,	green  and  blue to use, respectively.	If the
	      first form (a single number) is used, the	 image	will  be  dis-
	      played in monochrome (i.e., grayscale).

       -width number
	      Specifies	 the  width of the image, in pixels.	This option is
	      useful primarily in situations where the user wishes to build up
	      the  contents of the image piece by piece.  A value of zero (the
	      default) allows the image to expand or  shrink  horizontally  to
	      fit the data stored in it.

IMAGE COMMAND
       When a photo image is created, Tk also creates a new command whose name
       is the same as the image.  This command may be used to  invoke  various
       operations on the image.	 It has the following general form:
	      imageName option ?arg arg ...?
       Option and the args determine the exact behavior of the command.

       Those options that write data to the image generally expand the size of
       the image, if necessary, to accommodate the data written to the	image,
       unless  the  user  has  specified non-zero values for the -width and/or
       -height configuration options, in which case the width  and/or  height,
       respectively, of the image will not be changed.

       The following commands are possible for photo images:

       imageName blank
	      Blank  the image; that is, set the entire image to have no data,
	      so it will be displayed as transparent, and  the	background  of
	      whatever window it is displayed in will show through.

       imageName cget option
	      Returns  the  current value of the configuration option given by
	      option.  Option may have any of the values accepted by the image
	      create photo command.

       imageName configure ?option? ?value option value ...?
	      Query  or modify the configuration options for the image.	 If no
	      option is specified, returns a list describing all of the avail-
	      able options for imageName (see Tk_ConfigureInfo for information
	      on the format of this list).  If option  is  specified  with  no
	      value,  then the command returns a list describing the one named
	      option (this list will be identical to the corresponding sublist
	      of  the  value  returned	if no option is specified).  If one or
	      more option-value pairs are specified, then the command modifies
	      the  given  option(s)  to have the given value(s);  in this case
	      the command returns an empty string.  Option may have any of the
	      values accepted by the image create photo command.

       imageName copy sourceImage ?option value(s) ...?
	      Copies a region from the image called sourceImage (which must be
	      a photo image) to the  image  called  imageName,	possibly  with
	      pixel  zooming and/or subsampling.  If no options are specified,
	      this command copies the whole  of	 sourceImage  into  imageName,
	      starting	at  coordinates	 (0,0)	in  imageName.	 The following
	      options may be specified:

	      -from x1 y1 x2 y2
		     Specifies a rectangular sub-region of the source image to
		     be	 copied.  (x1,y1) and (x2,y2) specify diagonally oppo-
		     site corners of the rectangle.  If	 x2  and  y2  are  not
		     specified,	 the  default value is the bottom-right corner
		     of the source image.  The pixels copied will include  the
		     left and top edges of the specified rectangle but not the
		     bottom or right edges.  If the -from option is not given,
		     the default is the whole source image.

	      -to x1 y1 x2 y2
		     Specifies	a  rectangular	sub-region  of the destination
		     image to be affected.  (x1,y1) and (x2,y2) specify diago-
		     nally  opposite  corners  of the rectangle.  If x2 and y2
		     are not specified, the default value is (x1,y1) plus  the
		     size of the source region (after subsampling and zooming,
		     if specified).  If x2 and y2 are  specified,  the	source
		     region will be replicated if necessary to fill the desti-
		     nation region in a tiled fashion.

	      -shrink
		     Specifies that the size of the destination	 image	should
		     be reduced, if necessary, so that the region being copied
		     into is at the bottom-right corner of  the	 image.	  This
		     option  will  not affect the width or height of the image
		     if the user has specified a non-zero value for the -width
		     or -height configuration option, respectively.

	      -zoom x y
		     Specifies that the source region should be magnified by a
		     factor of x in the X direction and y in the Y  direction.
		     If	 y  is	not given, the default value is the same as x.
		     With this option, each pixel in the source image will  be
		     expanded  into a block of x x y pixels in the destination
		     image, all the same color.	 x and y must be greater  than
		     0.

	      -subsample x y
		     Specifies that the source image should be reduced in size
		     by using only every xth pixel in the X direction and  yth
		     pixel in the Y direction.	Negative values will cause the
		     image to be flipped about the Y or X axes,	 respectively.
		     If y is not given, the default value is the same as x.

	      -compositingrule rule
		     Specifies	how transparent pixels in the source image are |
		     combined with the destination image.  When a  compositing |
		     rule  of overlay is set, the old contents of the destina- |
		     tion image are visible,  as  if  the  source  image  were |
		     printed  on  a  piece of transparent film and placed over |
		     the top of the destination.  When a compositing  rule  of |
		     set is set, the old contents of the destination image are |
		     discarded and  the	 source	 image	is  used  as-is.   The |
		     default compositing rule is overlay.

       imageName data ?option value(s) ...?
	      Returns  image  data  in	the  form  of  a string. The following
	      options may be specified:

	      -background color
		     If the color is specified, the data will not contain  any
		     transparency  information.	 In all transparent pixels the
		     color will be replaced by the specified color.

	      -format format-name
		     Specifies the name of the image file format handler to be
		     used.   Specifically,  this  subcommand  searches for the
		     first handler whose name matches an initial substring  of
		     format-name  and  which  has  the capability to read this
		     image data.  If this option is not given, this subcommand
		     uses  the	first  handler that has the capability to read
		     the image data.

	      -from x1 y1 x2 y2
		     Specifies	a  rectangular	region	of  imageName  to   be
		     returned.	 If  only  x1 and y1 are specified, the region
		     extends from (x1,y1) to the bottom-right corner of image-
		     Name.   If	 all  four coordinates are given, they specify
		     diagonally opposite corners of  the  rectangular  region,
		     including	x1,y1  and  excluding  x2,y2.  The default, if
		     this option is not given, is the whole image.

	      -grayscale
		     If this options is specified, the data will  not  contain
		     color  information.  All  pixel  data will be transformed
		     into grayscale.

       imageName get x y
	      Returns the color of the pixel at coordinates (x,y) in the image
	      as  a list of three integers between 0 and 255, representing the
	      red, green and blue components respectively.

       imageName put data ?option value(s) ...?
	      Sets pixels in  imageName to the data specified in  data.	  This
	      command  first  searches	the list of image file format handlers
	      for a handler that can interpret the  data  in  data,  and  then
	      reads  the  image encoded within into imageName (the destination
	      image).  If data does not match any known format, an attempt  to
	      interpret	 it  as	 a (top-to-bottom) list of scan-lines is made,
	      with each scan-line being a (left-to-right) list of pixel colors
	      (see  Tk_GetColor	 for  a	 description  of valid colors.)	 Every
	      scan-line must be of the same length.  Note that when data is  a
	      single  color name, you are instructing Tk to fill a rectangular
	      region with that color.  The following options may be specified:

	      -format format-name
		     Specifies the format of the image data in data.  Specifi-
		     cally, only image file format handlers whose names	 begin
		     with  format-name	will  be  used	while searching for an
		     image data format handler to read the data.

	      -to x1 y1 ?x2 y2?
		     Specifies the coordinates of the top-left corner  (x1,y1)
		     of	 the region of imageName into which data from filename
		     are to be read.  The default is (0,0).  If x2,y2 is given
		     and data is not large enough to cover the rectangle spec-
		     ified by this option, the image data  extracted  will  be
		     tiled  so	it  covers  the	 entire destination rectangle.
		     Note that if data specifies a single color value, then  a
		     region  extending	to the bottom-right corner represented
		     by (x2,y2) will be filled with that color.

       imageName read filename ?option value(s) ...?
	      Reads image data from the file named filename  into  the	image.
	      This  command  first searches the list of image file format han-
	      dlers for a handler that can interpret the data in filename, and
	      then reads the image in filename into imageName (the destination
	      image).  The following options may be specified:

	      -format format-name
		     Specifies the format  of  the  image  data	 in  filename.
		     Specifically, only image file format handlers whose names
		     begin with format-name will be used while	searching  for
		     an image data format handler to read the data.

	      -from x1 y1 x2 y2
		     Specifies a rectangular sub-region of the image file data
		     to be copied to the destination image.  If only x1 and y1
		     are  specified,  the  region  extends from (x1,y1) to the
		     bottom-right corner of the image in the image  file.   If
		     all  four	coordinates are specified, they specify diago-
		     nally opposite corners or the region.   The  default,  if
		     this  option  is not specified, is the whole of the image
		     in the image file.

	      -shrink
		     If this option, the size of imageName will be reduced, if
		     necessary,	 so  that the region into which the image file
		     data are read is at the bottom-right corner of the image-
		     Name.  This option will not affect the width or height of
		     the image if the user has specified a non-zero value  for
		     the -width or -height configuration option, respectively.

	      -to x y
		     Specifies the coordinates of the top-left corner  of  the
		     region  of imageName into which data from filename are to
		     be read.  The default is (0,0).

       imageName redither
	      The dithering algorithm used in displaying photo	images	propa-
	      gates  quantization  errors from one pixel to its neighbors.  If
	      the image data for imageName is supplied in pieces, the dithered
	      image  may  not  be exactly correct.  Normally the difference is
	      not noticeable, but if it is a problem, this command can be used
	      to recalculate the dithered image in each window where the image
	      is displayed.

       imageName transparency subcommand ?arg arg ...?
	      Allows examination and manipulation of the transparency informa- |
	      tion in the photo image.	Several subcommands are available:     |

	      imageName transparency get x				       |
	      y					  |			       |
		     Returns a boolean indicating if the  pixel	 at  (x,y)  is |
		     transparent.					       |

	      imageName transparency set x y				       |
	      boolean				|			       |
		     Makes the pixel at (x,y) transparent if boolean is	 true, |
		     and makes that pixel opaque otherwise.		       |

       imageName write filename ?option value(s) ...?
	      Writes  image data from imageName to a file named filename.  The
	      following options may be specified:

	      -background color
		     If the color is specified, the data will not contain  any
		     transparency  information.	 In all transparent pixels the
		     color will be replaced by the specified color.

	      -format format-name
		     Specifies the name of the image file format handler to be
		     used  to  write the data to the file.  Specifically, this
		     subcommand searches for  the  first  handler  whose  name
		     matches an initial substring of format-name and which has
		     the capability to write an image file.  If this option is
		     not  given,  this	subcommand uses the first handler that
		     has the capability to write an image file.

	      -from x1 y1 x2 y2
		     Specifies a rectangular region of imageName to be written
		     to	 the image file.  If only x1 and y1 are specified, the
		     region extends from (x1,y1) to the bottom-right corner of
		     imageName.	 If all four coordinates are given, they spec-
		     ify  diagonally  opposite	corners	 of  the   rectangular
		     region.  The default, if this option is not given, is the
		     whole image.

	      -grayscale
		     If this options is specified, the data will  not  contain
		     color  information.  All  pixel  data will be transformed
		     into grayscale.

IMAGE FORMATS
       The photo image code is structured to  allow  handlers  for  additional
       image  file formats to be added easily.	The photo image code maintains
       a list of these handlers.  Handlers are added to the list by  register-
       ing  them  with	a  call to Tk_CreatePhotoImageFormat.  The standard Tk
       distribution comes with handlers for PPM/PGM and GIF formats, which are
       automatically registered on initialization.

       When reading an image file or processing string data specified with the
       -data configuration option, the photo image code invokes	 each  handler
       in  turn	 until one is found that claims to be able to read the data in
       the file or string.  Usually this will find the correct handler, but if
       it  doesn't, the user may give a format name with the -format option to
       specify which handler to use.  In fact the photo image  code  will  try
       those  handlers	whose  names  begin  with the string specified for the
       -format option (the comparison is case-insensitive).  For  example,  if
       the user specifies -format gif, then a handler named GIF87 or GIF89 may
       be invoked, but a handler named JPEG may not (assuming that  such  han-
       dlers had been registered).

       When writing image data to a file, the processing of the -format option
       is slightly different: the string value given for  the  -format	option
       must  begin  with  the  complete name of the requested handler, and may
       contain additional information following that, which  the  handler  can
       use,  for  example, to specify which variant to use of the formats sup-
       ported by the handler.  Note that not all image	handlers  may  support |
       writing transparency data to a file, even where the target image format |
       does.

COLOR ALLOCATION
       When a photo image is displayed in a window, the photo image code allo-
       cates colors to use to display the image and dithers the image, if nec-
       essary, to display a reasonable approximation to the  image  using  the
       colors  that  are available.  The colors are allocated as a color cube,
       that is, the number of colors allocated is the product of the number of
       shades of red, green and blue.

       Normally,  the  number of colors allocated is chosen based on the depth
       of the window.  For example, in an 8-bit PseudoColor window, the	 photo
       image  code  will attempt to allocate seven shades of red, seven shades
       of green and four shades of blue, for a total  of  198  colors.	 In  a
       1-bit  StaticGray  (monochrome)	window,	 it  will allocate two colors,
       black and white.	 In a 24-bit DirectColor or TrueColor window, it  will
       allocate	 256 shades each of red, green and blue.  Fortunately, because
       of the way that pixel values can be combined in DirectColor  and	 True-
       Color  windows,	this only requires 256 colors to be allocated.	If not
       all of the colors can be allocated, the photo image  code  reduces  the
       number of shades of each primary color and tries again.

       The  user  can  exercise	 some control over the number of colors that a
       photo image uses with  the  -palette  configuration  option.   If  this
       option  is used, it specifies the maximum number of shades of each pri-
       mary color to try to allocate.  It can also be used to force the	 image
       to be displayed in shades of gray, even on a color display, by giving a
       single number rather than three numbers separated by slashes.

CREDITS
       The photo image type was designed and implemented  by  Paul  Mackerras,
       based  on  his  earlier	photo  widget  and  some suggestions from John
       Ousterhout.

EXAMPLE
       Load an image from a file and tile it to the size of a window, which is
       useful for producing a tiled background:
	      # These lines should be called once
	      image create photo untiled -file "theFile.ppm"
	      image create photo tiled

	      # These lines should be called whenever .someWidget changes
	      # size; a <Configure> binding is useful here
	      set width	 [winfo width .someWidget]
	      set height [winfo height .someWidget]
	      tiled copy untiled -to 0 0 $width $height -shrink


SEE ALSO
       image(n)

KEYWORDS
       photo, image, color

Tk				      4.0			      photo(n)
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