ce-636 4_image interpretation

8/10/2019 Ce-636 4_image Interpretation

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IMAGE INTERPRETATION An image is a detailed photographic documentation

or record of features on the ground at the time ofdata acquisition. Such acquired images are examined by an analyst

in a systematic manner with the help of somesupporting information collected from maps, fieldvisit reports, or previously interpreted images of thesame area.

The interpretation of the information is carried out onthe basis of certain physical characteristics of theobject s! and phenomena appearing in the image.

The success of an image interpretation is dependentupon the " experience of the analyst, " the type of object or phenomena being interpreted, and

" the quality of the image .


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INTERPRETATION PROCEDURE #hotographic$%mage %nterpretation is defined as the

act of examining photographic images for thepurpose of identifying objects and judging theirsignificance.

The image interpretation procedure is a complextas&, and requires several tas&s to be conducted ina well'defined routine consisting of the process of

i! classification,ii! enumeration,iii! mensuration, andiv! delineation.


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Classification is the first tas& to beperformed by an interpreter, where basedon the appearance of an object or feature,the analyst assigns a class or informational

group .i! (etectionii! )ecognition

iii! %dentificationiv! *numeration


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The analyst first carries out the determination ofpresence or absence of an object or phenomenathrough the process of detection . This is followed by recognition where an object orphenomena is assigned an identity to a class orcategory. This generally requires a higher level of&nowledge of feature.

+inally, the feature is identified with a certain degreeof confidence to a specific class. This process is&nown as identification .

Enumeration is the next step, and it relates tolisting and counting of objects or phenomena thatare visible on an image. owever, it is dependentupon the ability of the analyst to classify itemsaccurately.


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*/*0*1TS

S%2* S A#*

T31* T*4T5)* #ATT*)1

S A(3 ASS36%AT%31 S%T*


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SIZESi-e of objects in an image is a function ofscale .%t is important to assess the si-e of a targetrelative to other objects in a scene, as well asits absolute si-e, to aid in the interpretation.

A quic& approximation of target si-e can resultinto direct interpretation more quic&ly.

+or example, if an interpreter has identified anarea with a number of buildings, then largebuildings such as factories or warehouseswould suggest commercial property, whereassmall buildings would indicate residential use.


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SHAPE

Shape normally refers to the general formor outline of individual features. %t is a very distinctive clue for interpretation. 1ormally, man'made features tend to have

defined edges leading to regular shape ,while natural objects will be having irregularshape .

)oads, canals, buildings are man'made

objects, and have regular shape while forestareas7 water bodies tend to have irregularshape.


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TONE

Tone of an object or phenomena refers to therelative brightness or colour in an image.

%t is one of the fundamental elements for

distinguishing between different objects orphenomena, and is a qualitative measure. 8enerally, tone is designated as dar&, medium

or light .


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PATTERN

Patte n refers to the spatial arrangement ofvisibly discernable objects .

Typically, the repetition of similar tones and

texture produces a distinctive andrecogni-able pattern.

+or example, houses laid out in orderlymanner in urban area or the trees in anorchard create different patterns


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ROAD

HOUSE


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TE!TURE

Te"t# e is referred to as the frequency oftonal changes in particular areas of an image. Texture is a qualitative characteristic, and is

normally categori-ed as rough or smooth.

An area of dry sand will appear on an imagehaving smooth texture, since the variation oftone for long stretches is not present.

Similarly, an area covered with forest havingvariety of tree species with varying canopysi-e, shape, and density will appear with arough texture, as tone will be changing veryrapidly.


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ROUGH

SMOOTH


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SHADO$

Sha%o& is an important characteristic ofimage interpretation.

%t gives an idea of the profile and relativeheight of an object, hence ma&ingidentification easier.

%n mountainous areas, shadow is an importantcharacteristic of images as it enhances theground topography, and hence helpful foridentifying variations in geological landforms.


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ASSOCIATION

Association is another importantcharacteristic as it considers the interrelation with the objects within the close proximity ofan object or phenomena.

+or example, white irregular patches adjacentto river indicate presence of dry sand ban&s ofthe river.

A regular grid of lines having small regularshaped box li&e objects is an indication ofurban areas.


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SITE

Site refers to the vocational characteristics of objects such as topography, soil,vegetation, and cultural features.

The primary ordering of each element in the

interpretation procedure with respect todegree of complexity.


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HEIRARCH'

AssociationSite Tertiary

P i(a )

Spatial

arrangements oftone

Tone/Colour

Size Shape

Texture

HeightSha o!

"attern

De* ee ofco(ple"it)

Secon%a )

Higher

Or er of Element of "hoto #nterpretation


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IMAGE INTERPRETATION STRATEGIES An image interpretation strategy can be defined

as a disciplined procedure that enables theinterpreter to relate geographic patterns on theground to their appearance on the image.

+ive categories of image interpretation strategieshave been defined as discussed below.

i! +ield 3bservationii! (irect )ecognition

iii! %nterpretation by %nferenceiv! #robabilistic %nterpretationsv! (eterministic %nterpretation


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FIELD O+SER,ATION

0any a times, the ground conditions as depicted onan image is complex, and an interpreter on the basisof his &nowledge and experience, is unable tocorrelate the relationships between ground andimage.

ence, the analyst is forced to visit the ground toma&e proper identification.

+ield observation is an important part of anyinterpretation tas& in order to assess the accuracy ofidentification.


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DIRECT RECOGNITION

(irect recognition is the application of aninterpreter9s experience, s&ill, and judgment toassociate the image patterns with informationalclasses.

This process is essentially a qualitative andsubjective analysis of the image using the elementsof image interpretation as visual and logical clues.

8enerally, direct recognition is an intuitive process,and hence, it requires very careful and systematicexamination of the image.


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INTERPRETATION +' INFERENCE ere, the analyst identifies information on the

basis of the presence of some other informationto which it is closely related to. Such inference information is &nown as surrogate

or proxy .

+or example, as soil distributions are closelyrelated to patterns of landforms and vegetationthat are recorded on the image, landforms andvegetation form surrogates for the soil pattern,and hence the interpreter infers the invisible soil

distribution from patterns that are visible. Application of this strategy requires a complete&nowledge of the lin& between the proxy and thedistribution.


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#)3:A:%/%ST%6 %1T*)#)*TAT%31 Sometimes, an object or phenomena is correlated to

certain specific characteristics e.g. , certain crops willbe grown as per time or season. This non'image information or &nowledge can be

utili-ed in probabilistic interpretation.

3ften such &nowledge can be expressed as astatement of probability.


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DETERMINISTIC INTERPRETATION (eterministic interpretation is the most rigorous and

precise approach. (eterministic interpretations are based upon

quantitatively expressed relationships that tie imagecharacteristics to ground conditions.

%n contrast with the other methods, most informationis derived from the image itself.

#hotogrammetric analysis of stereopairs for terraininformation is a good example of deterministicinterpretation.


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%mage interpreters, of course, may apply a mixtureof several strategies in a given situation.

%nterpretation of soil patterns, for example, may

require direct recognition to identify specific classesof vegetation, than application of interpretation byproxy to relate the vegetation pattern to theunderlying soil pattern.


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PHOTOMORPHIC ANAL'SIS

Another approach to interpretation of complexpatterns is to identify areas of uniform appearanceon the image, i.e., search for photomorphic regions.

ere the interpreter does not attempt to resolve the

individual components within the landscape, butloo&s for their combined influence on image pattern. #hotomorphic regions then are simply image

regions of relatively uniform tone and texture .


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%n the first step, the interpreter delineates

regions of uniform image appearance usingtone, texture, shadow, and the other elementsof image interpretation as a means ofseparating regions, and then tries to matchphotomorphic regions to useful classes ofinterest.

This step obviously requires field observationsor collateral information, because regionscannot be identified by image informationalone.

As the interpretation is refined, the interpretermay find that it is necessary to combine ordivide photo regions to produce an acceptableinterpretation.


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IMAGE INTERPRETATION -E'S %mage interpretation &eys are valuable aids forsummari-ing complex information. Such &eys serve either or both of the two

purposes;

i! A means of training in experiencedpersonnel in the interpretation of complex orunfamiliar topics.

ii! A reference aid for experienced interpreters to

organi-e information and examples pertaining tospecific topics.


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An image interpretation key is simply a

reference material designed to permitrapid and accurate identification of objectsor features represented on images.

A &ey usually consists of two parts.

i! The first part is a collection ofannotated or captioned images or stereo'grams.

ii! The second part is a graphic and$orword description.


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IMAGE INTERPRETATION -E'S

A &ey, then, is not a substitute forexperience and &nowledge of an interpreterbut a means of systematically orderedinformation to help in the interpretationprocess so that a user can learn quic&ly.

The interpretation &ey forms an effectiveway of organi-ing and presenting the expert&nowledge of a few individuals.

The construction of a &ey tends to sharpenone9s interpretation s&ills and encouragesthe interpreter to thin& more clearly aboutthe interpretation process.


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COMPARISON


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COMPARISON,is#al Di*ital

%t is a traditional approach based onhuman intuition, and its success is

experienced based.

%t is a recent approach andrequires speciali-ed training.

%t requires simple and inexpensiveequipment.

%t is complex, highly mathematicaland requires expensiveequipment.

%t uses the brightness characteristicsof the object, and accounts for thespatial content of the image.

%t relies heavily upon thebrightness and spectral content ofthe object and does not use thespatial content of the image.

5sually a single band of data is usedfor analysis. owever, colourproducts generated from three bandsof data, can be used for analysis.

0ultiple bands of data are usedfor analysis.

The analysis process is subjective,qualitative, and dependent on analystbias, but deductions are concrete.

The process is objective andquantitative in nature, yet abstractin nature.

DIGITAL IMAGE PROCESSING


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(igital (ata

%nitial Statistics *xtraction

%mage )ectification < )estoration

%nitial (isplay of %mage

%mage *nhancement

%mage 6lassification

=isual Analysis

Supervised5nsu pervised

6lassified output

#ost'processing operations

Ancillary (ata

(ata merging

Assessment of Accuracy

(ata)eport0aps and %mages

DIGITAL IMAGE PROCESSING


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STEPS IN DIGITAL ANAL'SISInitial Data Statistics

%nitial statistics provides an insight into the raw data asreceived from satellite.

Statistical information such as the minimum and

maximum values of the data set, mean, standarddeviation, and variance for each band are calculated. %nter'band relationships through variance'covariance and

correlation matrixes are examined. istogram and scatterograms provide a graphic view of

the nature of data for different bands. These are important statistical information required for

the next stage of preprocessing and imageenhancement.


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I(a*e Enhance(ent

The purpose of image enhancement is to improvethe appearance of the imagery and to assist insubsequent visual interpretation and analysis.

1ormally, image enhancement involves techniquesfor increasing the visual distinctions betweenfeatures by improving tonal distinction betweenvarious features in a scene using technique ofcontrast stretching.

The enhanced images can be displayed

interactively on a monitor or recorded in a hardcopyformat, either in blac& and white or colour.


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+urther, in multi'band data set, when the

spectral range of bands are located very closeto each other, repetitive information availableleads to redundancy of data.

#rincipal 6omponent Analysis helps in

reducing the number of bands for analysis andhence redundancy.


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hen the decisions are based on the geometricshapes, si-es, and pattern present in the imagedata, the classification procedure falls into thedomain of spatial pattern recognition .

The categori-ed data may be used to producethematic maps and$or summary of statistics onthe areas covered by each land cover type.

There are a variety of approaches to perform

digital image classification7 however, only twogeneric approaches most commonly used ares#pe /ise% and #ns#pe /ise% classification


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Data Me *in* an% GIS Inte* ation

(ata merging techniques are applied tocombine data for a given geographic area withother geographically referenced data set of thesame area.

The other data sets may be image datagenerated on other dates by the same sensoror by other remote sensing systems.

The data merging technique is frequently usedto combine remotely sensed data with othersources of information in the context of a8eographic %nformation System 8%S!.


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%n the next session % shall now be discussing

the various steps in digital image processing indetails.

ce-636 4_image interpretation

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