Provided by: tk8.5-doc_8.5.19-3_all 
NAME
photo - Full-color images
SYNOPSIS
image create photo ?name? ?options?
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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 transparent 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 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 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.
-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 write a string containing this image data. If
this option is not given, this subcommand uses a format that consists of a list (one
element per row) of lists (one element per pixel/column) of colors in “#rrggbb” format
(where rr is a pair of hexadecimal digits for the red channel, gg for green, and bb for
blue).
-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 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.
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 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 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 transparency subcommand ?arg arg ...?
Allows examination and manipulation of the transparency information in the photo image. Several
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
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 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 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.
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(3tk)
KEYWORDS
photo, image, color
Tk 4.0 photo(3tk)