photo
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 transpar-
ent. 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.
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 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 prece-
dence.
-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, spec-
ifying 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 dis-
played 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 avail-
able 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 oppo-
site 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 diago-
nally 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 desti-
nation 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.
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 a 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 image-
Name. 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 in filename into imageName (the destination
image). The following options may be specified:
-format format-name
Specifies the format of the image data in data. Specifi-
cally, 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 returned. 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.
-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 image-
Name. 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 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 han-
dlers 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 diago-
nally 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 propa-
gates 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 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 a 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 spec-
ify 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 register-
ing 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 sup-
ported by the handler.
COLOR ALLOCATION
When a photo image is displayed in a window, the photo image code allo-
cates colors to use to display the image and dithers the image, if nec-
essary, 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 True-
Color 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 pri-
mary 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.
KEYWORDS
photo, image, color
Tk 4.0 photo(n)
