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NAME

       photo - Full-color images

SYNOPSIS

       image create photo ?name? ?options?
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DESCRIPTION

       A  photo  is  an  image  whose  pixels  can display any color or be transparent.  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 should contain binary data or, for
              some formats, base64-encoded data (this is currently guaranteed to be supported for  GIF  images).
              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 precedence.

       -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, specifying 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
              displayed 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 available 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 opposite 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  diagonally  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 destination 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  destination
                     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 write a string containing this image data.  If
                     this option is not given, this subcommand uses a  format  that  consists  of  a  list  (one
                     element  per  row)  of  lists  (one element per pixel/column) of colors in “#rrggbb” format
                     (where rr is a pair of hexadecimal digits for the red channel, gg for  green,  and  bb  for
                     blue).

              -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 imageName.  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.   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.

              -to x1 y1 ?x2 y2?
                     Specifies the coordinates of the top-left corner (x1,y1) of the region  of  imageName  into
                     which the image data will be copied.  The default position is (0,0).  If x2,y2 is given and
                     data is not large enough to cover the rectangle specified 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 handlers 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  diagonally  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 imageName.
                     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 propagates 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 information 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 specify 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
       registering 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 does not, 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 handlers 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 supported 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 allocates colors to use to display the
       image and dithers the image, if necessary, 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 TrueColor 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  primary
       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(3tk)

KEYWORDS

       photo, image, color