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
