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 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, 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
image(3tk)
photo, image, color