img-png3tk

Usage

Overview

package require img::png

Like all packages of Img it does not provide new commands, but extends the existing Tk command image, so that it supports files containing raster images in the Portable Network Graphics format (png). More specifically img::png extends Tk's photo [https://www.tcl.tk/man/tcl9.0/TkCmd/photo.html] image type.

The name of the new format handler is png. This handler provides new additional configuration options. See section Options for more detailed explanations.

All of the above means that in a call like image create photo ?name? ?options?

In addition the value of option -format is treated as a list and may contain any of the special options listed in section Options.

The package img::png is a sub-package of Img. It can be loaded as a part of the complete Img support, via package require Img, or on its own, via package require img::png.

Notes

[1]

Chapter Image Metadata of the Img manual page describes the parameters of the resolution related options.

Options

The handler provides the following options:

-verbose bool

This option is supported for reading and writing. Available since version 1.4.6.

If set to true, additional information about the read or written image is printed to stdout. Default is false.

-alpha double

This option is supported for reading only. Available since version 1.4.2.

An additional alpha filtering value for the overall image, which allows the background on which the image is displayed to show through. This usually also has the effect of desaturating the image. The alpha value must be between 0.0 and 1.0. Specifying an alpha value, overrides the setting of the -withalpha flag, i.e. reading a file which has no alpha channel (Grayscale, RGB) will add an alpha channel to the image independent of the -withalpha flag setting.

-gamma double

This option is supported for reading only. Available since version 1.4.6.

Use the specified gamma value when reading an image. This option overwrites gamma values specified in the file. If this option is not specified and no gamma value is in the file, a default value of 1.0 is used.

-withalpha bool

This option is supported for reading and writing. Available since version 1.4.1.

If set to false, an alpha channel is ignored during reading or writing. Default is true.

Note: This option was named -matte in previous versions and is still recognized.

-resolution xres ?yres?

This option is supported for writing only. Available since version 2.0.

Set the resolution values of the written image file. If yres is not specified, it is set to the value of xres.

If option is not specified, the DPI and aspect values of the metadata dictionary are written. If no metadata values are available, no resolution values are written.

-xresolution xres

This option is supported for writing only. Available since version 2.0.

Set the horizontal resolution value of the written image file.

-yresolution yres

This option is supported for writing only. Available since version 2.0.

Set the vertical resolution value of the written image file.

-tag key value

This option is supported for writing only. Available since version 2.0.

Each key-value pair will be written as a named text chunk where the key provides the name of the chunk and the value its contents. Currently the maximum number of -tag specifications are 10.