photo(n) manual page
Table of Contents
photo - Full-color images
image create
photo ?name? ?options?
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.
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 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.
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 read this image data. If this option is not
given, this subcommand uses the first handler that has the capability to
read the image data.
- -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 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.
- 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.
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 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.
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
image(n)
photo, image, color
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