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photo(n) Tk Built-In Commands photo(n)
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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 trans-parent transparent
parent 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 for-mat format
mat 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 informa-tion information
tion 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 correspond-ing corresponding
ing 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 speci-fied, specified,
fied, 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 pix-els pixels
els 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 sub-sampling subsampling
sampling 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 direc-tion direction
tion 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 rectan-gular rectangular
gular 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 bottomright
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 for-mat format
mat 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 destina-tion destination
tion 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 speci-fied, specified,
fied, 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. Sev-eral Several
eral 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 spec-ified: specified:
ified:
-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 han-dlers handlers
dlers 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 (mono-chrome) (monochrome)
chrome) 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 sepa-rated separated
rated by slashes.
CREDITS
The photo image type was designed and implemented by Paul Mackerras, based on his earlier photo wid-get widget
get 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(n)
KEYWORDS
photo, image, color
Tk 4.0 photo(n)
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