Digital Image Processing( الرقمية الصور (معالجة

• Definition: Computer-based manipulation and interpretation of digital images.

Digital Image Processing

• Five broad types of computer assisted operation:

1. Image rectification and restoration (preprocessingا2. Image enhancement

3. Image classification (spectral vs. spatial pattern recognition)

4. Data merging and GIS integration

5. Hyperspectral image analysis

6. Biophysical modeling

7. Image transmission and compression

Image Rectification & Restoration

( الصورة (تصحيح

• Preprocessing ( االولية to correct (المعالجةالصور ) distorted or degraded image data(تصحيح)(المشوهة

– Geometric distortions ( الهندسية (التصحيحات– Radiometric calibration( االشعاعية (التصحيحات– Elimination of noise ( الضوضاء (ازالة

Image Enhancement ( الصورة (توضيح

• To more effectively display or record the data, increasing the visual distinctions between features in a scene

• Contrast manipulation: stretching

Image Classification ( تصنيف(الصورة

• To determine the land cover identity of each pixel in an image, replacing visual analysis with quantitative techniques

• Spectral pattern recognition:– using only spectral radiances

• Spatial pattern recognition: – using geometric shapes, sizes and patterns

Image Classification

• The overall objective of classification is to categorize all pixels in a digital image into one of several land cover classes

• Themes thematic maps: A map designed to demonstrate particular features or concepts.

Examples of Classification Results

Data Merging and GIS Integration ( دمج

(البيانات• To combine image data with other geographically

referenced datasets for the same area

– Multitemporal data merging

– Change detection procedures

– Multisensor image merging

Image Rectification & Restoration( الصورة (تصحيح

• To correct image data for distortions or degradations stemming from the image acquisition process

• Varies with: – Type of device (camera, scanner)– Platform (airborne versus satellite)– Total field of view- A sensor with a wide field of view can

image the same place from different angles more frequently than a sensor in the same orbit with a narrower field of view and smaller swath

Image Rectification & Restoration

Digital images ( الرقمية (الصور

• Remote sensing images are recorded in digital forms• A digital image is a two-dimensional array of pixels. • Each pixel has an intensity value (represented by a

digital number) and a location address (referenced by its row and column numbers).

• They are distributed in computer compatible tapes (CCTs)

• The basic unit is pixel that is represented as a digital number (DN)

• Different data sets may use different number of bits so that bit scaling is common.

Image processing systems( اللرقمية المعالجة (انظمة

• Computer hardware (e.g. PC) • Computer software • Operating system (e.g. Windows/NT) • Image processing software (e.g. ENVI) • Operator (e.g. you)

Geometric Correction( الهندسي (التصحيح

• Raw digital images usually contain geometric distortions so significant that they cannot be used directly as a map base without subsequent processing.

• Distortion (التشوه)-changes in shape and position of objects with respect to their true shape and position.

• The source of distortions:– Variations in altitude, attitude (position), and velocity of sensor

platform

– Panoramic distortion

– Earth curvature

– Atmospheric refraction

– Relief displacement

Image registration (or resampling)( الصورة (تسجيل

• Resampling ( الصورة The calculation of-(تسجيلnew DN for pixels created during geometric correction of a digital scene, based on the values in the local area around the uncorrected pixels.

• In the Nearest Neighbor ( االقرب technique, the (الجارtransformed pixel takes the value of the closest pixel in the pre-shifted array.

• Bilinear Interpolation ( الخطية uses the 4 closest:(الزيادةpixel values surrounding the transformed output pixel is used.

• Cubic Convolution ( المكعبي uses the 16 closest :(االلتواءpixel values

Image registration (or resampling)

Image registration (or resampling)

(Radiometric(Radiometric correction correction))(( االشعاعية االشعاعية التصحيحات ((التصحيحات

Atmospheric EffectsAtmospheric Effects

Lapp=apparent radiance measured by sensor

ρ = reflectance of objectT = atmospheric transmittanceE = irradiance on object, incomingLp = path radiance/haze, from the atmosphere and not from the object

LPTE

LAPP