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Photo(3pm)	      User Contributed Perl Documentation	    Photo(3pm)

NAME
       Tk::Photo - Full-color images

SYNOPSIS
           $widget->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, XBM, XPM, BMP, JPEG, PNG 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
       transparencySet subcommand.

CREATING PHOTOS
       Photos are created using the Photo method.  Photo supports 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 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 METHODS
       When a photo image is created, Tk also creates a new object.  This
       object supports the configure and cget methods described in Tk::options
       which can be used to enquire and modify the options described above.

       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 addition methods are available for photo images:

       $image->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.

       $image->copy(sourceImage ?,option value(s) ...?)
	   Copies a region from the image called $sourceImage (which must be a
	   photo image) to the image called $image, possibly with pixel
	   zooming and/or subsampling.	If no options are specified, this
	   method copies the whole of $sourceImage into $image, starting at
	   coordinates (0,0) in $image.	 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.

       $image->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 method searches for the first
		   handler whose name matches a initial substring of format-
		   name and which has the capability to read this image data.
		   If this option is not given, this method uses the first
		   handler that has the capability to read the image data.

	   -from => x1, y1, ?, x2, y2?
		   Specifies a rectangular region of $image to be returned.
		   If only x1 and y1 are specified, the region extends from
		   (x1,y1) to the bottom-right corner of $image.  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.

       $image->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.

       $image->put(data ?,-format=>format-name? ?,-to=> x1 y1 ?x2 y2??)
	   Sets pixels in $image 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 $image (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 =>x, y ?, x2, y2?
	       Specifies the coordinates of the top-left corner (x1,y1) of the
	       region of $image 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 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.

       $image->read(filename ?,option value(s), ...?)
	   Reads image data from the file named filename into the image.  This
	   method 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 $image (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 is specified, the size of $image 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.	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 $image into which data from filename are to be
		   read.  The default is (0,0).

       $image->redither
	   The dithering algorithm used in displaying photo images propagates
	   quantization errors from one pixel to its neighbors.	 If the image
	   data for $image 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 method can be used to recalculate the
	   dithered image in each window where the image is displayed.

       $image->transparency(subcommand, ?arg, arg ...?);
	   Allows examination and manipulation of the transparency information
	   in the photo image.	Several subcommands are available:

	   $image->transparencyGet(x, y);
	       Returns a boolean indicating if the pixel at (x,y) is
	       transparent.

	   $image->transparencySet(x, y, boolean);
	       Makes the pixel at (x,y) transparent if boolean is true, and
	       makes that pixel opaque otherwise.

       $image->write(filename ?,option value(s), ...?)
	   Writes image data from $image 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 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 $image 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
		   $image.  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 XBM, XPM, BMP, JPEG,
       PNG and PPM/PGM 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.  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.

SEE ALSO
       Tk::Bitmap Tk::Image Tk::Pixmap

KEYWORDS
       photo, image, color

perl v5.26.0			  2017-07-22			    Photo(3pm)
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