


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  (24  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.


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

       :channel channelId
              channelId  gives the name of a port open for reading which is to
              be read to supply data for the photo image.  The data format  in
              the port must be one of those for which there is an image format
              handler that can read data from a file or port.

       :data string
              Specifies the contents of the image as a string.  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
              from a file or port.

       :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



STk                            3.1                              1





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


              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.





STk                            3.1                              2





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


       (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



STk                            3.1                              3





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


                     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.

       (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   imageName 'put data :to x1 y1 x2 y2)
              Sets pixels in imageName to the colors specified in data.   data
              is  used to form a two-dimensional array of pixels that are then
              copied into the imageName.  data is structured as a list of hor-
              izontal  rows,  from  top  to bottom, each of which is a list of
              colors, listed from left to right.  Each color may be  specified
              by  name  (e.g.,  blue)  or in hexadecimal form (e.g., #2376af).
              The :to option can be used to specify the area of  imageName  to
              be affected.  If only x1 and y1 are given, the area affected has
              its top-left corner at (x1,y1) and is the same size as the array
              given  in data.  If all four coordinates are given, they specify
              diagonally opposite corners of the affected rectangle,  and  the
              array given in data will be replicated as necessary in the X and
              Y directions to fill the rectangle.

       (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



STk                            3.1                              4





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


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

              :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 a 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.

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.




STk                            3.1                              5





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


       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.


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.





STk                            3.1                              6





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


SEE ALSO
       bitmap, make-image, image, jpeg, pixmap























































STk                            3.1                              7


