Image interpretation I and IIgrel.ist.edu.pk/lms/pluginfile.php?file=/2181/mod...visual interpretation. • There are two color display methods: color composite, to generate color

Image interpretation I and II

“Looking at satellite image,

identifying different objects,

according to scale and associated

information and to communicate

this information to others is what

we call as

IMAGE INTERPRETATION” (Lillesand & Kiefer, 2004)

Fundamentals of Image Interpretation

– Level of Interpretation may vary from simple to complex

– Interpretation complexity varies with the type of subjected landcovers

– Interpretation success depends upon the quality of satellite

data (Spatial, Spectral and Radiometric Resolutions)

– Success of Image interpretation depends on the experience of interpreter

Key to Visually Interpret a Satellite Image

• Name of satellite

(LANDSAT, SPOT, IKONOS etc)

• Type (Spectral Mode) of satellite data

(Panchromatic, Multispectral etc)

• Band combination used

(432, 742, 541 etc)

• Satellite image acquisition date and ancillary information about the area

Elements of Image Interpretation • Colour

• Tone

• Texture

• Pattern

• Shape

• Shadow

• Association

• Resolution

• Scale

Colour

• Color display of remote-sensing data is of importance for effective visual interpretation.

• There are two color display methods: color composite, to generate color with multi-band data, and pseudo-color display , to assign different colors to the grey scale of a single image.

A Color Composite image can be generated by composing

three selected single-band images with the use of three

primary colors i.e. RGB

Different color images may be obtained depending upon the

selection of three band images and the assignment of the three

primary colors.

Colour Display Types

– True Colour Composites

Natural colour composites render features similarly as the human eyes

sees them.

They can be prepared by using Landsat TM bands 3 (red), 2 (green), and 1 (blue) for the RGB primary colours.

The advantage is that they are easy to understand also for laymen, the disadvantage is that the blue band is strongly affected by atmospheric haze and is not available from most sensors.

False Colour Composites

–In addition, invisible regions, such as infrared, are often used, which need to be displayed in colour. As a colour composite within an infrared band is no longer natural colour, it is called a false colour composite (FCC).

–In particular, the colour composite with the assignment of blue to the green band, green to the red band, and red to the near infrared band is very popular.

Landsat-5, False Color

Composite (FCC)

Blue

Green

Red

TM Band-4 (IR)

TM Band-2 (Green)

TM Band-3 Red

Forming a False Color Composite Image (FCC)

Tone – Relative brightness / Darkness in the image

Texture – Rate of change of tonal variation per unit area on the satellite

Image.

For example, homogeneous grassland exhibits a smooth texture,

dense and tall forest usually show a coarse texture. Depends upon the scale of the photograph or image

Pattern

– Spatial arrangement of the objects in a satellite image data

– Pattern is a regular, usually repeated, shape in respect to an object.

– For example, rows of houses or apartments, regularly-spaced rice fields, interchanges of highways, orchards, and so on, can

provide information from their unique patterns.

Shape

– The specific shape of an object, as it is viewed from above, will be imaged as a vertical photograph.

– For example, the crown of a conifer tree looks like a circle, while that of a deciduous tree has an irregular

shape.

– Airports, factories, and so on can also be identified by their shapes.

Size

A proper photo-scale (image resolution) should be selected

depending on the purpose of the interpretation.

Shadow

Shadow is usually a visual obstacle for image

interpretation. However, shadow can also give height

information about a tower, tall building, mountain ranges,

and others, as well as shape information from the non

vertical perspective-such as the shape of a bridge.

Association

A specific combination of elements, geographic characteristics,and configuration of the surroundings, or the context, of an object can

provide the user with specific information for image

interpretation.