Tk::Photo - Full-color images
$widget->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, XBM, XPM,
BMP, JPEG, PNG 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 transparencySet subcommand.
Photos are created using the Photo method. Photo
supports 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 object. This
object supports the configure and cget methods described in
Tk::options which can be used to enquire and modify the options described
above.
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 addition methods are available for photo images:
- $image->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.
- $image->copy(sourceImage
?,option value(s) ...?)
- Copies a region from the image called
$sourceImage (which must be a
photo image) to the image called
$image, possibly with pixel
zooming and/or subsampling. If no options are specified, this method
copies the whole of
$sourceImage into
$image, starting at
coordinates (0,0) in $image.
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.
- $image->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 method 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
method uses the first handler that has the capability to read the image
data.
- -from => x1,
y1, ?, x2, y2?
- Specifies a rectangular region of
$image to be returned. If
only x1 and y1 are specified, the region extends from
(x1,y1) to the bottom-right corner of
$image. 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.
- $image->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.
- $image->put(data
?,-format=>format-name? ?,-to=> x1 y1 ?x2
y2??)
- Sets pixels in $image 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
$image (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 =>x, y
?, x2, y2?
- Specifies the coordinates of the top-left corner (x1,y1) of
the region of $image 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.
- $image->read(filename
?,option value(s), ...?)
- Reads image data from the file named filename into the image. This
method 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
$image (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 is specified, the size of
$image 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. 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
$image into which data from
filename are to be read. The default is (0,0).
- $image->redither
- The dithering algorithm used in displaying photo images propagates
quantization errors from one pixel to its neighbors. If the image data for
$image 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 method can be used to
recalculate the dithered image in each window where the image is
displayed.
- $image->transparency(subcommand,
?arg, arg ...?);
- Allows examination and manipulation of the transparency information in the
photo image. Several subcommands are available:
- $image->transparencyGet(x,
y);
- Returns a boolean indicating if the pixel at (x,y) is
transparent.
- $image->transparencySet(x,
y, boolean);
- Makes the pixel at (x,y) transparent if boolean is
true, and makes that pixel opaque otherwise.
- $image->write(filename
?,option value(s), ...?)
- Writes image data from $image
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
$image 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
$image. 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 XBM, XPM, BMP, JPEG, PNG
and PPM/PGM 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.
Tk::Bitmap Tk::Image Tk::Pixmap