photo(n) - phpMan

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 for-
mats 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.

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 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 for-
mat 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 verti-
cally 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 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 horizon-
tally 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 nec-
essary, 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 dis-
played 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 speci-
fied, 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 speci-
fied 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 speci-
fied:

-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 nec-
essary, 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 config-
uration 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. Nega-
tive 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 con-
tents 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 desti-
nation. When a compositing rule of set is set, the old contents of the des-
tination 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 infor-
mation. In all transparent pixels the color will be replaced by the speci-
fied color.

-format format-name
Specifies the name of the image file format handler to be used. Specifi-
cally, this subcommand searches for the first handler whose name matches an
initial substring of format-name and which has the capability to write a
string containing this image data. If this option is not given, this sub-
command uses a format that consists of a list (one element per row) of lists
(one element per pixel/column) of colors in "#rrggbb" format (where rr is a
pair of hexadecimal digits for the red channel, gg for green, and bb for
blue).

-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 respec-
tively.

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 des-
tination 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 rectan-
gle specified by this option, the image data extracted will be tiled so it
covers the entire destination rectangle. Note that if data specifies a sin-
gle color value, then a region extending to the bottom-right corner repre-
sented 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 des-
tination 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 sup-
plied in pieces, the dithered image may not be exactly correct. Normally the dif-
ference 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 infor-
mation. In all transparent pixels the color will be replaced by the speci-
fied 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 han-
dler 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 bot-
tom-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 stan-
dard Tk distribution comes with handlers for PPM/PGM and GIF formats, which are automati-
cally registered on initialization.

When reading an image file or processing string data specified with the -data configura-
tion 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 cor-
rect 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 han-
dlers had been registered).

When writing image data to a file, the processing of the -format option is slightly dif-
ferent: 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.

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 approxi-
mation 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 num-
ber 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 num-
ber 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.

EXAMPLE
Load an image from a file and tile it to the size of a window, which is useful for produc-
ing 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