Subversion Repositories or1k

'\"

'\" Copyright (c) 1994 The Australian National University

'\" Copyright (c) 1994-1997 Sun Microsystems, Inc.

'\"

'\" See the file "license.terms" for information on usage and redistribution

'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.

'\"

'\" Author: Paul Mackerras (paulus@cs.anu.edu.au),

'\"         Department of Computer Science,

'\"         Australian National University.

'\"

'\" RCS: @(#) $Id: photo.n,v 1.1.1.1 2002-01-16 10:25:49 markom Exp $

'\"

.so man.macros

.TH photo n 4.0 Tk "Tk Built-In Commands"

.BS

'\" Note:  do not modify the .SH NAME line immediately below!

.SH NAME

photo \- Full-color images

.SH SYNOPSIS

\fBimage create photo \fR?\fIname\fR? ?\fIoptions\fR?

.BE

.SH DESCRIPTION

.PP

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.

.SH "CREATING PHOTOS"

.PP

Like all images, photos are created using the \fBimage create\fR

command.

Photos support the following \fIoptions\fR:

.TP

\fB\-data \fIstring\fR

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 \fB\-data\fR

and \fB\-file\fR options are specified, the \fB\-file\fR option takes

precedence.

.TP

\fB\-format \fIformat-name\fR

Specifies the name of the file format for the data specified with the

\fB\-data\fR or \fB\-file\fR option.

.TP

\fB\-file \fIname\fR

\fIname\fR 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.

.TP

\fB\-gamma \fIvalue\fR

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.

.TP

\fB\-height \fInumber\fR

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.

.TP

\fB\-palette \fIpalette-spec\fR

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

\fIpalette-spec\fR 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).

.TP

\fB\-width \fInumber\fR

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.

.SH "IMAGE COMMAND"

.PP

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:

.CS

\fIimageName option \fR?\fIarg arg ...\fR?

.CE

\fIOption\fR and the \fIarg\fRs

determine the exact behavior of the command.

.PP

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

\fB\-width\fR and/or \fB\-height\fR configuration options, in which

case the width and/or height, respectively, of the image will not be

changed.

.PP

The following commands are possible for photo images:

.TP

\fIimageName \fBblank\fR

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.

.TP

\fIimageName \fBcget\fR \fIoption\fR

Returns the current value of the configuration option given

by \fIoption\fR.

\fIOption\fR may have any of the values accepted by the

\fBimage create photo\fR command.

.TP

\fIimageName \fBconfigure\fR ?\fIoption\fR? ?\fIvalue option value ...\fR?

Query or modify the configuration options for the image.

If no \fIoption\fR is specified, returns a list describing all of

the available options for \fIimageName\fR (see \fBTk_ConfigureInfo\fR for

information on the format of this list).  If \fIoption\fR is specified

with no \fIvalue\fR, 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 \fIoption\fR is specified).  If

one or more \fIoption\-value\fR 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.

\fIOption\fR may have any of the values accepted by the

\fBimage create photo\fR command.

.TP

\fIimageName \fBcopy\fR \fIsourceImage\fR ?\fIoption value(s) ...\fR?

Copies a region from the image called \fIsourceImage\fR (which must

be a photo image) to the image called \fIimageName\fR, possibly with

pixel zooming and/or subsampling.  If no options are specified, this

command copies the whole of \fIsourceImage\fR into \fIimageName\fR,

starting at coordinates (0,0) in \fIimageName\fR.  The following

options may be specified:

.RS

.TP

\fB\-from \fIx1 y1 x2 y2\fR

Specifies a rectangular sub-region of the source image to be copied.

(\fIx1,y1\fR) and (\fIx2,y2\fR) specify diagonally opposite corners of

the rectangle.  If \fIx2\fR and \fIy2\fR 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 \fB\-from\fR

option is not given, the default is the whole source image.

.TP

\fB\-to \fIx1 y1 x2 y2\fR

Specifies a rectangular sub-region of the destination image to be

affected.  (\fIx1,y1\fR) and (\fIx2,y2\fR) specify diagonally opposite

corners of the rectangle.  If \fIx2\fR and \fIy2\fR are not specified,

the default value is (\fIx1,y1\fR) plus the size of the source

region (after subsampling and zooming, if specified).  If \fIx2\fR and

\fIy2\fR are specified, the source region will be replicated if

necessary to fill the destination region in a tiled fashion.

.TP

\fB\-shrink\fR

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

\fB\-width\fR or \fB\-height\fR configuration option, respectively.

.TP

\fB\-zoom \fIx y\fR

Specifies that the source region should be magnified by a factor of

\fIx\fR in the X direction and \fIy\fR in the Y direction.  If \fIy\fR

is not given, the default value is the same as \fIx\fR.  With this

option, each pixel in the source image will be expanded into a block

of \fIx\fR x \fIy\fR pixels in the destination image, all the same

color.  \fIx\fR and \fIy\fR must be greater than 0.

.TP

\fB\-subsample \fIx y\fR

Specifies that the source image should be reduced in size by using

only every \fIx\fRth pixel in the X direction and \fIy\fRth pixel in

the Y direction.  Negative values will cause the image to be flipped

about the Y or X axes, respectively.  If \fIy\fR is not given, the

default value is the same as \fIx\fR.

.RE

.TP

\fIimageName \fBget\fR \fIx y\fR

Returns the color of the pixel at coordinates (\fIx\fR,\fIy\fR) in the

image as a list of three integers between 0 and 255, representing the

red, green and blue components respectively.

.TP

\fIimageName \fBput \fIdata\fR ?\fB\-to\fI x1 y1 x2 y2\fR?

Sets pixels in \fIimageName\fR to the colors specified in \fIdata\fR.

\fIdata\fR is used to form a two-dimensional array of pixels that are

then copied into the \fIimageName\fR.  \fIdata\fR 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

\fB\-to\fR option can be used to specify the area of \fIimageName\fR to be

affected.  If only \fIx1\fR and \fIy1\fR are given, the area affected

has its top-left corner at (\fIx1,y1\fR) and is the same size as the

array given in \fIdata\fR.  If all four coordinates are given, they

specify diagonally opposite corners of the affected rectangle, and the

array given in \fIdata\fR will be replicated as necessary in the X and

Y directions to fill the rectangle.

.TP

\fIimageName \fBread\fR \fIfilename\fR ?\fIoption value(s) ...\fR?

Reads image data from the file named \fIfilename\fR into the image.

This command first searches the list of

image file format handlers for a handler that can interpret the data

in \fIfilename\fR, and then reads the image in \fIfilename\fR into

\fIimageName\fR (the destination image).  The following options may be

specified:

.RS

.TP

\fB\-format \fIformat-name\fR

Specifies the format of the image data in \fIfilename\fR.

Specifically, only image file format handlers whose names begin with

\fIformat-name\fR will be used while searching for an image data

format handler to read the data.

.TP

\fB\-from \fIx1 y1 x2 y2\fR

Specifies a rectangular sub-region of the image file data to be copied

to the destination image.  If only \fIx1\fR and \fIy1\fR are

specified, the region extends from (\fIx1,y1\fR) 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.

.TP

\fB\-shrink\fR

If this option, the size of \fIimageName\fR 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 \fIimageName\fR.  This option

will not affect the width or height of the image if the user has

specified a non-zero value for the \fB\-width\fR or \fB\-height\fR

configuration option, respectively.

.TP

\fB\-to \fIx y\fR

Specifies the coordinates of the top-left corner of the region of

\fIimageName\fR into which data from \fIfilename\fR are to be read.

The default is (0,0).

.RE

.TP

\fIimageName \fBredither\fR

The dithering algorithm used in displaying photo images propagates

quantization errors from one pixel to its neighbors.

If the image data for \fIimageName\fR 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.

.TP

\fIimageName \fBwrite \fIfilename\fR ?\fIoption value(s) ...\fR?

Writes image data from \fIimageName\fR to a file named \fIfilename\fR.

The following options may be specified:

.RS

.TP

\fB\-format\fI format-name\fR

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

\fIformat-name\fR 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.

.TP

\fB\-from \fIx1 y1 x2 y2\fR

Specifies a rectangular region of \fIimageName\fR to be written to the

image file.  If only \fIx1\fR and \fIy1\fR are specified, the region

extends from \fI(x1,y1)\fR to the bottom-right corner of

\fIimageName\fR.  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.

.RE

.SH "IMAGE FORMATS"

.PP

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 \fBTk_CreatePhotoImageFormat\fR.  The

standard Tk distribution comes with handlers for PPM/PGM and GIF formats,

which are automatically registered on initialization.

.PP

When reading an image file or processing

string data specified with the \fB\-data\fR 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 \fB\-format\fR 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

\fB\-format\fR option (the comparison is case-insensitive).  For

example, if the user specifies \fB\-format gif\fR, then a handler

named GIF87 or GIF89 may be invoked, but a handler

named JPEG may not (assuming that such handlers had been

registered).

.PP

When writing image data to a file, the processing of the

\fB\-format\fR option is slightly different: the string value given

for the \fB\-format\fR 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.

.SH "COLOR ALLOCATION"

.PP

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.

.PP

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.

.PP

The user can exercise some control over the number of colors that a

photo image uses with the \fB\-palette\fR 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.

.SH CREDITS

.PP

The photo image type was designed and implemented by Paul Mackerras,

based on his earlier photo widget and some suggestions from

John Ousterhout.

.SH KEYWORDS

photo, image, color