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 v5.40.1 2025-04-13 Photo(3pm)
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