### 28.1.4 Viewing images

Starting from Xcas version 1.9.0, image objects are viewed by using the display command. The legacy Xcas image structure can be visualized by exporting it to a file by using the writergb command (see Section 28.1.5).

- display takes one mandatory arguments and one optional argument:
  - img, an image object.
  - Optionally, either a,b, a pair of real numbers, or a+i b, a complex number (by default, a=b=0).
- display(img ⟨,a,b ⟩) or display(img ⟨,a+i b ⟩) returns a graphic object showing img with (a,b) corresponding to its lower-left corner. The axes are automatically hidden and the view is orthonormalized in order to preserve the original aspect ratio of the image.

In the examples that follow, we assume that the current directory in Xcas is changed (by using the cd command, see Section 4.2.1) to /usr/local/share/giac/examples in Linux resp. to C:\xcaswin\examples in Windows.

#### Example

img:=image("Exemples/demo/terre.jpg")

an image of size 512×256 (RGB) |  |  |  |  |  |  |  |  |  |

display(img)

Multiple images can be shown together by calling display several times within a single command line (delimited by ;) and adjusting a and b to appropriate values in each call. If desired, individual image captions can be inserted by using the legend command (See Section 21.4.10 for an example.) There is also a possibility of combining images with other graphical objects.

display(img); legend(285+125 i,"Africa",color=gold); legend(270+200 i,"Europe",color=gold); legend(380+190 i,"Asia",color=yellow); legend(430+90 i,"Australia",color=yellow); legend(100+190 i,"North America",color=gold); legend(160+80 i,"South America",color=gold);

##### Viewing images as textures.

Xcas can also display image files in rectangles in 2D or on surfaces in 3D with the gl_texture property of the object (see Section 19.1.2). This procedure does not use image objects, but reads images from disk.

#### Examples

rectangle(0,200,1/2,gl_texture="Exemples/demo/terre.jpg")

sphere([0,0,0],1,gl_material=[gl_texture,"Exemples/demo/terre.jpg"])