Assignment 5 - nested loops in images

You can create an image with the image create command

Syntax: image create type ?name? ?option value ...?

Create a new image.

type	The type of image. May be photo for multicolor images, or bitmap for bitmap images.
?name?	An optional name for this image. If not provided, Tcl will assign a name.
?option value ...?	Keyword/Value pairs that define the image object. Options include -height and -width, etc.

You can retrieve individual pixels from an image with the $imageName get command.

Syntax: imageName get xLoc yLoc

Retrieve RGB values from an image

imageName	The name of the image as returned by image create
xloc yloc	The x and y location for the pixel

You can assign a value to a pixel with the $imageName put command.

Syntax: imageName put colorList -to x1 y1 ?x2 y2?

Set pixel values in an image

imageName	The name of the image as returned by image create
colorList	A list of colors to assign to the pixels in Tcl color format.
-to x1 y1 ?x2 y2?	The X/Y location for a pixel, or a rectangular area for a set of pixels.

The format of the pixel needs to be something like #rrggbb where rr is a 2 digit hex value for the red intensity, etc.

To encode 3 decimal values into a Tcl color, use the format command:

Syntax: format formatString ?data1? ?data2? ...

The format command returns a new string based on a format definition and a set of data values.

format	Returns a new string, formatted as defined by the formatString string.
data#	Data to substitute into the format string.

The format string to use for this is #02x02x02x.

An image can be written to a file with the imageName write command:

Syntax: imageName write fileName -format fmt

Write an image to a file.

imageName	The name of the image as returned by image create
fileName	Path to the file to create
-format fmt	Define the image format for the file. By default the format is ppm. The gif format is supported by default.

Write a Tcl script that will create an image and fill it with values that fade from blue at the top to green at the bottom and then save the image to a file named earthNsky.ppm.

You can test your code with any image viewing software that supports the ppm format - gimp or xview on a Linux system, or openoffice on Windows and Mac systems. Other viewing tools or the Tk/Wish canvas can also be used.