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 (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
              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
              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
              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.

       (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
              horizontal 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
              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 '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
                     specify 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
       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 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
       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.


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.


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



STk                                   3.1                             photo(n)
