The IMAGE function displays image data in a graphics window.

Example

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The following lines create the image shown at the top of this topic.

; Display an image.

file1 = FILEPATH('Night.jpg', $

   SUBDIRECTORY=['examples','data'])

; The image spans [-180,180], [-90,90],

; with a lower-left pixel at [-180,-90].

; Restrict the range to one hemisphere.

im1 = IMAGE(file1, $

   BACKGROUND_COLOR="midnight blue", $

   IMAGE_DIMENSIONS=[360,180], $

   IMAGE_LOCATION=[-180,-90], $

   XRANGE=[-180,0], YRANGE=[-90,90], $

   DIMENSIONS=[512,512], MARGIN=0)

; Overplot another image, same dimensions.

file2 = FILEPATH('Day.jpg', $

   SUBDIRECTORY=['examples','data'])

   im2 = IMAGE(file2, /OVERPLOT, $

   IMAGE_DIMENSIONS=[360,180], $

   IMAGE_LOCATION=[-180,-90], $

   TRANSPARENCY=50)

t = TEXT(-175, 80, '$\it Day/Night$', $

   /DATA, FONT_SIZE=20)

; Fade between the two.

for i=-100,100 do im2.TRANSPARENCY=abs(i)

Additional Examples

See Image examples for additional examples using the IMAGE function, or see Image with a Map Projection for an example of applying a map projection to a map image.

Syntax

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graphic = IMAGE( Data [, X, Y ] [, Keywords=value] [, Properties=value] [, Map Properties=value] [, Map Grid Properties=value] )

graphic = IMAGE( Filename [, Keywords=value] [, Properties=value] [, Map Properties=value] [, Map Grid Properties=value] )

Keywords

Keywords are applied only during the initial creation of the graphic.

[, AXIS_STYLE={0|1|2|3}] [, /BUFFER] [, /CURRENT] [, /DEVICE] [, DIMENSIONS=array] [, GEOTIFF=structure] [, IMAGE_DIMENSIONS=array] [, IMAGE_LOCATION=array] [, LAYOUT=array] [, LOCATION=array] [, MARGIN=array] [, /NODATA] [, /ORDER] [, OVERPLOT=1 or variable] [, WINDOW_TITLE=string]

Properties

Properties can be set as keywords to the function during creation, or retrieved or changed using the "." notation after creation.

ASPECT_RATIO, AXES, BACKGROUND_COLOR, BACKGROUND_TRANSPARENCY, CLIP, CROSSHAIR, FONT_COLOR, FONT_NAME, FONT_SIZE, FONT_STYLE, GRID_UNITS, HIDE, INTERPOLATE, MAPGRID, MAPPROJECTION, MAP_PROJECTION, MAX_VALUE, MIN_VALUE, NAME, POSITION, RGB_TABLE, TITLE, TRANSPARENCY, UVALUE, WINDOW, XRANGE, YRANGE, ZVALUE

Methods

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Close

ConvertCoord

CopyWindow

Delete

GetData

GetValueAtLocation

MapForward

MapInverse

Order

Print

Refresh

Rotate

Save

Scale

Select

SetData

Translate

Return Value

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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

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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

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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. See Format Codes for more information.
[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 length of each major tick mark, normalized to the width or height of the graphic. The default value is automatically calculated based upon the aspect ratio of the graphic.
[XYZ]TICKNAME	A string array containing the tick labels.
[XYZ]TICKUNITS	A string giving the tick units. Valid values are: null (the default, signified by empty quotes), Years, Months, Days, Hours, Minutes, Seconds, Time, exponent for exponential notation, or scientific for scientific 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.

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.

Or, set this keyword to an existing IDL Graphic reference to make that window be the current window and direct the new graphic to that 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.

Note: If GRID_UNITS is in "degrees" then IMAGE_DIMENSIONS should be set to the width and height of the image, in degrees, on the Earth's surface. If GRID_UNITS is in "meters" then IMAGE_DIMENSIONS should be set to the width and height of the image in meters. In this case, set the MAP_PROJECTION property to specify the actual map projection associated with the image.

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.

Note: If GRID_UNITS is in "degrees" then IMAGE_LOCATION should be set to the latitude and longitude of the lower-left corner of the image. If GRID_UNITS is in "meters," then IMAGE_LOCATION should be set to the X offset and Y offset of the lower-left corner of the image within the image's map projection. In this case, set the MAP_PROJECTION property to specify the actual map projection associated with the image.

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.

WINDOW_TITLE

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

Properties

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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 Functions to Control Mouse Events 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 map projection associated with this image. After creation, use this property to retrieve or set the current map projection. See below for a list of available map projections, projection properties, or grid properties.

If the image has GRID_UNITS in "degrees" (latitude and longitude), then IDL will use the specified map projection to set the projection for the entire dataspace. IDL will warp the image from degrees to meters and overlaid onto the map projection.

If the image's GRID_UNITS are "meters," IDL assumes the image is already projected into the specified map projection. In this case, use the IMAGE_DIMENSIONS and IMAGE_LOCATION properties to register the image at the correct map location. If you are placing this image into a new graphic dataspace, or the existing dataspace does not have a map projection, then IDL will apply the image's map projection to that dataspace. Finally, if the image's map projection matches the dataspace's map projection, IDL will overlay the image directly onto the map with no warping. If, however, the image's map projection does not match the projection of the current dataspace, IDL will warp the image from its projection to the dataspace's map projection.

MAX_VALUE

A scalar or array giving the maximum image data value to be used when displaying the image. For byte data the default is 255. For other data types the default is the maximum data value for each band. If a scalar value is provided then the same value is used for all bands in the image. If an array is provided, it should have three elements for an RGB image, or four elements for an RGBA image.

MIN_VALUE

A scalar or array giving the minimum image data value to be used when displaying the image. For byte data the default is 0. For other data types the default is the minimum data value for each band. If a scalar value is provided then the same value is used for all bands in the image. If an array is provided, it should have three elements for an RGB image, or four elements for an RGBA image.

Tip: If you have a byte image that does not span the entire 0-255 range, you could set the MIN_VALUE and MAX_VALUE properties to the minimum and maximum data value to stretch the data to fill the 0-255 range. Or, instead, you could set the RGB_TABLE to a color table that only contains colors that span your data values.

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.

POSITION

Set this property to a four-element vector that determines the position of the graphic within the window. The coordinates [X1, Y1, X2, Y2] define the lower left and upper right corners of the graphic. Coordinates are expressed in normalized units ranging from 0.0 to 1.0. On creation, if the DEVICE keyword is set, the units are given in device units (pixels).

Note: After creation, you can set the POSITION to either a two or four-element vector. If two elements are provided, the center of the graphic will be translated to that position. If four elements are provided, the graphics will be translated and scaled to fit the position.

RGB_TABLE

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

Tip: If you have a two-dimensional byte image that does not span the entire 0-255 range, you could set the RGB_TABLE to a table that only contains colors that span your data values. The COLORTABLE function can be used to construct custom color tables.

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.

Map Projections

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You can use the following map projections with the MAP_PROJECTION property:

Alaska Conformal Albers Equal Area Azimuthal Equidistant Cylindrical Equal Area Equidistant Conic Equirectangular Geographic Gnomonic Hammer

Hotine Oblique Mercator Integerized Sinusoidal Interrupted Goode Interrupted Mollweide Lambert Azimuthal Lambert Conformal Conic Mercator Miller Cylindrical

Mollweide Near Side Perspective Oblated Equal Area Orthographic Polar Stereographic Polyconic Robinson Sinusoidal

Space Oblique Mercator State Plane Stereographic Transverse Mercator UTM Van der Grinten Wagner IV Wagner VII

See the Map function for a description of the map projections.

Map Properties

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If you use the MAP_PROJECTION property to set the map projection, then you may need to set other properties to define the projection. The following properties may be set:

CENTER_LATITUDE CENTER_LONGITUDE ELLIPSOID FALSE_EASTING FALSE_NORTHING HEIGHT HOM_AZIM_ANGLE HOM_AZIM_LONGITUDE HOM_LATITUDE1

HOM_LATITUDE2 HOM_LONGITUDE1 HOM_LONGITUDE2 IS_JUSTIFY IS_ZONES LIMIT MERCATOR_SCALE OEA_ANGLE OEA_SHAPEM

OEA_SHAPEN SEMIMAJOR_AXIS SEMIMINOR_AXIS SOM_FLAG SOM_INCLINATION SOM_LANDSAT_NUMBER SOM_LANDSAT_PATH SOM_LONGITUDE

SOM_PERIOD SOM_RATIO SPHERE_RADIUS STANDARD_PAR1 STANDARD_PAR2 STANDARD_PARALLEL TRUE_SCALE_LATITUDE ZONE

To set these properties after creation, you can use the MAPPROJECTION property to retrieve a reference to the MapProjection object, and then set the properties on that object. See the Map function for a description of these properties.

Map Grid Properties

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The following map graticule (grid) properties are available on creation:

BOX_ANTIALIAS BOX_AXES BOX_COLOR BOX_THICK CLIP COLOR FILL_COLOR FONT_NAME FONT_SIZE

FONT_STYLE GRID_LATITUDE GRID_LONGITUDE HIDE HORIZON_COLOR HORIZON_LINESTYLE HORIZON_THICK LABEL_ALIGN

LABEL_ANGLE LABEL_COLOR LABEL_FILL_BACKGROUND LABEL_FILL_COLOR LABEL_FORMAT LABEL_POSITION LABEL_SHOW LABEL_VALIGN

LATITUDE_MAX LATITUDE_MIN LINESTYLE LONGITUDE_MAX LONGITUDE_MIN THICK TRANSPARENCY ZVALUE

You may also get or set a property after creation, and the request will automatically be passed down to the MapGrid object. Or, you can use the MAPGRID property to retrieve a reference to the MapGrid, and then get or set properties directly on that object. See the MAPGRID function for a description of these properties.

Version History

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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.
8.2.2	Change POSITION from a keyword to a property. Change MIN_VALUE and MAX_VALUE to be the min/max data values per band. Add table of map projection and map grid properties.

See Also

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!COLOR, Formatting IDL Graphics Symbols and Lines, PLOT, WINDOW, Using IDL graphics



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