photo - Full-color images
image create photo ?name? ?options?
imageName blank
imageName cget option
imageName configure ?option? ?value option value ...?
imageName copy sourceImage ?option value(s) ...?
imageName data ?option value(s) ...?
imageName get x y
imageName put data ?option value(s) ...?
imageName read filename ?option value(s) ...?
imageName redither
imageName transparency subcommand ?arg arg ...?
imageName write filename ?option value(s) ...?
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 PNG, 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.
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 PNG and 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.
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
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, the format is guessed from the file extension. If that cannot be
determined, 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.
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, PNG 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.
Some image formats support sub-options, which are specified at the
time that the image is loaded using additional words in the -format
option. At the time of writing, the following are supported:
- gif -index
indexValue
- When parsing a multi-part GIF image, Tk normally only accesses the first
image. By giving the -index sub-option, the indexValue'th
value may be used instead. The indexValue must be an integer from 0
up to the number of image parts in the GIF data.
- png -alpha
alphaValue
- An additional alpha filtering for the overall image, which allows the
background on which the image is displayed to show through. This usually
also has the effect of desaturating the image. The alphaValue must
be between 0.0 and 1.0.
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.
The photo image type was designed and implemented by Paul
Mackerras, based on his earlier photo widget and some suggestions from John
Ousterhout.
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
The PNG image loader allows the application of an additional alpha
factor during loading, which is useful for generating images suitable for
disabled buttons:
image create photo icon -file "icon.png"
image create photo iconDisabled -file "icon.png" \
-format "png -alpha 0.5"
button .b -image icon -disabledimage iconDisabled