photo(3Tk) photo(3Tk)
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 (24 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.
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 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 from a
file.
-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)
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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
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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.
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-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 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 ?-to x1 y1 x2 y2?
Sets pixels in imageName to the colors specified in data. data is
used to form a two-dimensional array of pixels that are then copied
into the imageName. data is structured as a list of horizontal
rows, from top to bottom, each of which is a list of colors, listed
from left to right. Each color may be specified by name (e.g.,
blue) or in hexadecimal form (e.g., #2376af). The -to option can be
used to specify the area of imageName to be affected. If only x1
and y1 are given, the area affected has its top-left corner at
(x1,y1) and is the same size as the array given in data. If all
four coordinates are given, they specify diagonally opposite corners
of the affected rectangle, and the array given in data will be
replicated as necessary in the X and Y directions to fill the
rectangle.
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
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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 write filename ?option value(s) ...?
Writes image data from imageName to a file named filename. The
following options may be specified:
-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 specify diagonally
opposite corners of the rectangular region. The default, if
this option is not given, is the whole image.
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
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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.
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.
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KEYWORDS
photo, image, color
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