The IMAGE function returns a reference to the created graphic. Use the returned reference to manipulate the graphic after creation by changing properties or calling methods.

Arguments

Data

A two-dimensional array of data, or a three-dimensional array containing RGB or RGBA pixel values. If Data is three-dimensional, then if any one of the dimensions is 3, it is assumed to represent the red, green, and blue channels. If Data is three-dimensional, then if any one of the dimensions is 4, it is assumed to represent the red, green, blue, and alpha channels.

Note: Data should be on a regularly-spaced grid. If the data is not gridded, refer to the GRIDDATA function to convert the data to a regular grid.

X

A vector representing the x-coordinates (the column locations) of the image grid. X should have the same number of elements as the number of image columns.

Y

A vector representing the y-coordinates (the row locations) of the image grid. Y should have the same number of elements as the number of image rows.

Tip: Instead of X and Y, you can also use the IMAGE_DIMENSIONS and IMAGE_LOCATION properties to define the image grid.

Keywords

AXIS_STYLE

Set this keyword to one of the following values:

0 - No axes. This is the default for images.
1 - Single X, Y (and Z if 3D) axes located at the minimum data value. This is the default for 3D graphics.
2 - Box axes - multiple axes located at both the minimum and maximum data values. This is the default for 2D graphics.
3 - Crosshair-style axes - located at the midpoint of each data dimension. This is the default for polar plots.

You can set the following properties on the axes:

Property	Description
[XYZ]COLOR	A string or RGB vector containing the axis color.
[XYZ]GRIDSTYLE	A string or integer giving the linestyle for tickmarks.
[XYZ]LOG	Set to 1 if the axis is logarithmic.
[XYZ]MAJOR	The number of major tick marks. Set to -1 to auto-compute, set to 0 to suppress.
[XYZ]MINOR	The number of minor tick marks. Set to -1 to auto-compute, set to 0 to suppress.
[XYZ]SHOWTEXT	Set to 1 to show text labels or 0 to hide the text labels.
[XYZ]STYLE	The axis range style. The valid values are: (0) "Nice" range. Default for all graphics except Image, Barplot, and Map. (1) Force the exact data range. Default for Image, Barplot, and Map. (2) Pad the axes slightly beyond the "nice" range. (3) Pad the axes slightly beyond the exact data range. Note: The [XYZ]RANGE takes precedence over this property.
[XYZ]SUBTICKLEN	The ratio of the minor tick length to the major tick length. The default is 0.5.
[XYZ]TEXT_COLOR	A string or RGB vector containing the axis text color.
[XYZ]TEXT_ORIENTATION	The angle (in degrees) of the tick mark labels.
[XYZ]TEXTPOS	Set to 1 to position text above the axis. The default is 0, below the axis.
[XYZ]THICK	Set to a floating-point value between 0 and 10 to specify the line thickness for tickmarks. A thickness of 0 gives a thin hairline. The default is 1.
[XYZ]TICKDIR	Set to 1 to draw the tickmarks facing outwards. The default is 0, facing inwards.
[XYZ]TICKFONT_NAME	A string containing the font name for the axis text.
[XYZ]TICKFONT_SIZE	The axis text size in points.
[XYZ]TICKFONT_STYLE	A string or integer containing the font style: "normal" (0), "bold" (1), "italic" (2), or "bold italic" (3).
[XYZ]TICKFORMAT	A string or string array of tick label formats.
[XYZ]TICKINTERVAL	The interval between major tick marks.
[XYZ]TICKLAYOUT	Set to 1 to suppress tick marks; set to 2 to draw a box around the tick labels.
[XYZ]TICKLEN	The normalized length of each major tick mark. Tick lengths < 0.25 are in arbitrary units that do not scale with the graphic. Larger tick lengths are normalized relative to the width of the graphic. The default is 0.05.
[XYZ]TICKNAME	A string array containing the tick labels.
[XYZ]TICKUNITS	A string giving the tick units. Valid values are "" (the default), "Years", "Months", "Days", "Hours", "Minutes", "Seconds", "Time", or "exponent" for exponential notation. If any of the time units are utilized, then the tick values are interpreted as Julian date/time values. If more than one unit is provided, the axis will be drawn with multiple levels.
[XYZ]TICKVALUES	An array of tick mark locations.
[XYZ]TITLE	A string giving the axis title.
[XYZ]TRANSPARENCY	An integer from 0-100 giving the percent transparency.

For more detailed explanations of these properties, see the AXIS function.

Tip: You can also use the AXIS function to insert additional axes after the graphic has been created.

BUFFER

Set this keyword to 1 to direct the graphics to an off-screen buffer instead of creating a window.

CURRENT

Set this keyword to create the graphic in the current window. If no window exists, a new window is created. The WINDOW's SetCurrent method may be used to set the current window.

DEVICE

Set this keyword if values are specified in device coordinates (pixels) for the MARGIN and POSITION properties. (Normalized coordinates are the default for these properties.)

DIMENSIONS

Set this keyword to a two-element vector of the form [width, height] to specify the window dimensions in pixels. If you do not specify a value for DIMENSIONS, IDL by default uses the values of the IDL_GR_WIN_HEIGHT and IDL_GR_WIN_WIDTH preferences for Windows platforms or the IDL_GR_X_HEIGHT and IDL_GR_X_WIDTH preferences for X Windows systems on UNIX.

GEOTIFF

Set this keyword equal to an anonymous structure containing the GeoTIFF tags from a GeoTIFF file. For information on GeoTIFF tags, see the GEOTIFF keyword in the READ_TIFF function.

IMAGE_DIMENSIONS

Set this keyword to a 2-element vector, [width, height], to specify the image dimensions (in data units). By default, the dimensions equal the number of columns and rows in the image. If this property is set then the X and Y arguments are ignored.

IMAGE_LOCATION

Set this keyword to a 2-element vector, [x, y], to specify the location of the lower-left pixel in data units. By default, the location is [0, 0]. If this property is set then the X and Y arguments are ignored.

LAYOUT

Set this keyword to a three-element vector [ncol, nrow, index] that arranges graphics in a grid. The first dimension ncol is the number of columns in the grid, nrow is the number of rows, and index is the grid position at which to place the graphic (starting at element 1). This property is ignored if either OVERPLOT or POSITION is specified.

LOCATION

Set this keyword to a two-element vector [X offset, Y offset] giving the window's screen offset in pixels.

MARGIN

Set this keyword to the current graphic's margin values in the layout specified by the LAYOUT property. Use a scalar value to set the same margin on all sides, or use a four-element vector [left, bottom, right, top] to specify different margins on each side.

By default, margin values are expressed in normalized units ranging from 0.0 to 0.5. If the DEVICE property is set, the values are given in device units (pixels).

This property is ignored if either OVERPLOT or POSITION is specified.

NODATA

Set this keyword to 1 to create the graphic, but without any data attached to it. The axes and title (if present) are also created and displayed. If the OVERPLOT keyword is specified, axis ranges will not change.

Note: You must still provide valid input arguments. The data range of the input arguments are used to automatically set the range of the axes. The [XYZ]RANGE properties may be used to override these default ranges.

ORDER

Set this keyword to force the rows of the image data to be drawn from top to bottom. By default, image data is drawn from the bottom row up to the top row.

OVERPLOT

Set this keyword to 1 (one) to place the graphic on top of the existing graphic in the current window. If no current window exists, a new window is created.

Set this property to an existing IDL Graphic reference to direct the new graphic to the window specified by the provided IDL Graphic reference.

POSITION

Set this keyword to a four-element vector that determines the location of the visualization within the graphic window. The coordinates x₀, y₀ represent the lower left and x₁, y₁ represent the upper right corners of the data space. Coordinates are expressed in normalized units ranging from 0.0 to 1.0. If the DEVICE property is set, the units are given in device units (pixels).

Note: When using POSITION, factor in enough space to display the title and axis labels. For example, if you use POSITION to place your visualization at 0 on the X or Y axis, any labels for that axis will not be visible.

WINDOW_TITLE

Set this keyword to the title of the IDL Graphic window. The title is displayed in the window's title bar.

Properties

ASPECT_RATIO

A floating point value indicating the ratio of the Y dimension to the X dimension in data units. If this property is set to a nonzero value, the aspect ratio will be preserved as the graphic is stretched or shrunk. The default value is 0 for all graphics except images, meaning that the aspect ratio is not fixed, but is allowed to change as the graphic is stretched or shrunk.

AXES (Get Only)

This property retrieves an array that contains all of the AXIS objects within the visualization. For example, for a plot visualization:

p = PLOT(/TEST)

ax = p.AXES

ax[0].TITLE = 'X axis'

ax[1].TITLE = 'Y axis'

ax[2].HIDE = 1 ; hide top X axis

ax[3].HIDE = 1 ; hide right Y axis

See AXIS for a list of the available properties.

BACKGROUND_COLOR

Set this property to a string or RGB vector indicating the graphic's background color. The default value is [255, 255, 255] (white). Set this property to a scalar value to remove the background color.

Tip: To set the background color of the entire window, retrieve the window object using the WINDOW property, and set the BACKGROUND_COLOR on the window object.

BACKGROUND_TRANSPARENCY

Set this property to an integer between 0 and 100 giving the percent transparency of the background color. The default is 100 (completely transparent).

Note: If the BACKGROUND_COLOR property is changed, and the current background transparency is 100, then the BACKGROUND_TRANSPARENCY will be automatically set to 0 (opaque) so that you can see the new color.

CLIP

Set this property to 1 to clip portions of the graphic that lie outside of the dataspace range, or to 0 to disable clipping. The default is 1.

CROSSHAIR (Get Only)

Use this property to retrieve a reference to the Crosshair graphic. All graphics objects within the same set of axes share a single Crosshair graphic. For Plot graphics the default behavior is to display the crosshair when the plot is selected. For other graphics the crosshair is disabled. The STYLE property may be used to control the automatic crosshair display, while the LOCATION property is used to manually draw a crosshair.

You can get and set the following properties on the retrieved crosshair:

Property	Description
ANTIALIAS	Set to 1 to enable anti-aliasing for the lines.
COLOR	A string or RGB vector containing the color.
HIDE	Set to 1 to hide the crosshair, 0 to show.
INTERPOLATE	Set to 1 to force interpolation between Plot data points when SNAP is active. For other graphics this property is ignored. The default is 0.
LINESTYLE	An integer or string giving the line style. The default is 'dot'.
LOCATION	The location at which to draw the crosshair. For Plot graphics, if SNAP is enabled, then only the X coordinate needs to be supplied. Otherwise, LOCATION should be set to a two-element vector [X, Y] for two-dimensional graphics or [X, Y, Z] for three-dimensional graphics. If STYLE is currently "None", then setting the LOCATION will automatically set the STYLE to "Manual".
NAME	The name of the graphic.
SNAP	Set to 1 to snap the crosshair to the nearest Plot data point. For other graphics this property is ignored. The default is 1.
STYLE	An integer or string giving the crosshair style. Possible values are: 0 - "None" - never draw the crosshair. This is the default. 1 - "Manual" - draw the crosshair using the LOCATION property. 2 - "Auto" - automatically draw the crosshair. This is the default for plots.
THICK	The thickness of the lines. The default is 1.
TRANSPARENCY	The percent transparency of the lines. The default is 50.
UVALUE	An IDL variable of any data type.

For example, use the CROSSHAIR property to draw a crosshair on an image:

im = IMAGE(/TEST, TRANSPARENCY=50, AXIS_STYLE=2)

c = im.CROSSHAIR

c.COLOR = 'red'

c.THICK = 2

c.LOCATION = [300, 200]

See Creating Mouse Event Functions for a more detailed crosshair example.

FONT_COLOR

Set this property to a string or RGB vector that specifies the text color for the title and axes (if present). The default value is "black".

FONT_NAME

Set this property equal to a string specifying the IDL or system font for the title and axes (if present). The default value is “Helvetica”.

FONT_SIZE

Set this property equal to an integer specifying the font size for the title and axes (if present). The default value is 16 points.

FONT_STYLE

Set this property equal to an integer or a string specifying the font style for the title and axes (if present). Allowed values are:

Integer	String	Resulting Style
0	"Normal" or "rm"	Default (roman)
1	"Bold" or "bf"	Bold
2	"Italic" or "it"	Italic
3	"Bold italic" or "bi"	Bold italic

GRID_UNITS

Set this property to a string or integer specifying the units for the image grid. This property applies only when a map projection is inserted. It has the following values:

0 or "" - None. The image grid is in arbitrary units that are not tied to a map projection. The image will not be warped to the current map projection.
1 or "m" or "meters" - Meters. The image grid is in meters, and is tied to a particular map projection. The image will be warped to the current map projection.
2 or "deg" or "degrees" - Degrees. The image grid is in degrees longitude/latitude, and will be automatically warped to the current map projection.

HIDE

Set this property to 1 to hide the graphic. Set HIDE to 0 to show the graphic.

INTERPOLATE

Set this property to 1 to display the image using bilinear interpolation. The default is to use nearest-neighbor interpolation.

MAPGRID (Get Only)

If a map projection is currently in effect, this property retrieves a reference to the MAPGRID object.

MAPPROJECTION (Get Only)

If a map projection is currently in effect, this property retrieves a reference to the MAPPROJECTION object.

MAP_PROJECTION

A string giving the name of the current map projection. After creation, use this property to retrieve or set the current map projection.

MAX_VALUE

The maximum image data value. Data values between MIN_VALUE and MAX_VALUE are scaled into the range 0 to 255. For byte image data the default is 255, while for non-byte data the default is the maximum data value.

MIN_VALUE

The minimum image data value. Data values between MIN_VALUE and MAX_VALUE are scaled into the range 0 to 255. For byte image data the default is 0, while for non-byte data the default is the minimum data value.

NAME

A string that specifies the name of the graphic. The name can be used to retrieve the graphic using the brackets array notation. If NAME is not set then a default name is chosen based on the graphic type.

RGB_TABLE

The number of the predefined IDL color table, or a 3 x 256 or 256 x 3 byte array containing color values to use for two-dimensional image data. If image is RGB or RGBA then this property is ignored.

TITLE

Set this property to a string specifying a title. If TITLE is specified, you can also specify any of the FONT_COLOR, FONT_NAME, FONT_SIZE, and FONT_STYLE properties to control the title appearance.

After creation the TITLE property may be used to retrieve a reference to the title text object, and the TEXT properties may be used to modify the title object.

You can also add Greek letters and mathematical symbols using a TeX-like syntax. These symbols need to be enclosed within a pair of "$" characters. See Adding Mathematical Symbols and Greek Letters to the Text String for details on the available symbols.

TRANSPARENCY

An integer between 0 and 100 that specifies the percent transparency of the image line. The default value is 0.

UVALUE

Set this property to an IDL variable of any data type.

WINDOW (Get Only)

This property retrieves a reference to the WINDOW object which contains the graphic.

XRANGE

A two-element vector giving the X data range to plot. The default behavior is to plot the entire data range.

YRANGE

A two-element vector giving the Y data range to plot. The default behavior is to plot the entire data range.

ZVALUE

Set this property to the height of the Z plane onto which the image will be projected. The default is 0.

Version History

8.0	Introduced
8.1	Added the following properties: CROSSHAIR, GEOTIFF, MAP_PROJECTION, MAPGRID, MAPPROJECTION, UVALUE, [XYZ]SHOWTEXT, [XYZ]STYLE, Added the following methods: Delete, GetData, GetValueAtLocation, MapForward, MapInverse, SetData.
8.2	Added AXES, BACKGROUND_COLOR, BACKGROUND_TRANSPARENCY, CLIP properties.
8.2.1	[XYZ]TICKUNITS accepts exponent as a value.

IMAGE

Example

Additional Examples

Syntax

Keywords

Properties

Methods

Return Value

Arguments

Data

X

Y

Keywords

AXIS_STYLE

BUFFER

CURRENT

DEVICE

DIMENSIONS

GEOTIFF

IMAGE_DIMENSIONS

IMAGE_LOCATION

LAYOUT

LOCATION

MARGIN

NODATA

ORDER

OVERPLOT

POSITION

WINDOW_TITLE

Properties

ASPECT_RATIO

AXES (Get Only)

BACKGROUND_COLOR

BACKGROUND_TRANSPARENCY

CLIP

CROSSHAIR (Get Only)

FONT_COLOR

FONT_NAME

FONT_SIZE

FONT_STYLE

GRID_UNITS

HIDE

INTERPOLATE

MAPGRID (Get Only)

MAPPROJECTION (Get Only)

MAP_PROJECTION

MAX_VALUE

MIN_VALUE

NAME

RGB_TABLE

TITLE

TRANSPARENCY

UVALUE

WINDOW (Get Only)

XRANGE

YRANGE

ZVALUE

Version History

See Also