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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 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 trans-parent transparent
       parent 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  for-mat format
              mat  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 informa-tion information
              tion 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 correspond-ing corresponding
              ing 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  speci-fied, specified,
              fied,  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  pix-els pixels
                     els  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 sub-sampling subsampling
                     sampling 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  direc-tion direction
                     tion  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 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 imageName.  If
                     all four coordinates are given, they specify diagonally opposite corners of the rectan-gular rectangular
                     gular  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 bottomright
                     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 for-mat format
                     mat 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 destina-tion destination
                     tion 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 speci-fied, specified,
                     fied, 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.  Sev-eral Several
              eral 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 spec-ified: specified:
              ified:

              -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 han-dlers handlers
       dlers 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 (mono-chrome) (monochrome)
       chrome) 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 sepa-rated separated
       rated by slashes.

CREDITS
       The photo image type was designed and implemented by Paul Mackerras, based on his earlier photo  wid-get widget
       get 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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