7 Elements of Image Interpretation | Remote Sensing and Photogrammetry

In this article we will learn about an interesting concept i.e., elements of image interpretation.

After, reading this article you will understand what is image interpretation, what are image interpretation elements and how they are useful in studying an image.

What is Image Interpretation?

Image interpretation is the study of photograph or image to extract useful information from the image by making use of interpretation elements.

What are Image Interpretation Elements?

These are the characteristics of objects observed in the image or photograph, and are useful for understanding and identification of information associated with it.

Following are the most widely used image interpretation elements.

1. Tone:

This is also often called as color. It is the most basic and fundamental element of image interpretation. However, there is a small difference. Tone is observed in panchromatic or mono-band images. While color is normally observed in a composite image consisting of red, green and blue bands. Tone is the first thing which an observer will look at while interpreting. In case of a single band image, tone is indicated by gray level. It helps in identifying and distinguishing objects, for example sand appears in white tone while water appears in black tone in case of a single band image.

2. Texture:

The variation in the tone is called texture. Texture is useful in understanding how uniform an object is. For example, large grassland will have uniform and simple texture, while the forest land tends to have a rough texture.

3. Pattern:

The arrangement of tone and texture in the image is defined as pattern. Pattern helps in distinguishing between man made and natural features. For example, most of the man made features such as cultivated orchards, row houses etc will have pattern. If pattern is not considered, an orchard could be confused with forest.

4. Size:

Though size is not the fundamental element one would look at while interpreting the images, it plays an important role in studying about the objects. For example, Objects with same texture and tone, but with different size can be interpreted in a different way. For example, an individual residential building can be separated from a residential apartment or shopping complex.

5. Shape:

Shape is another important element of photo interpretation. A peculiar shape is an easy thing to notice in a photograph. It can be interfered with related detail very easily depending on location and study area. Because, peculiar or uncommon shapes exist very few in number in any city.

6. Shadow:

The length of shadow in a image gives information about height and profile of an object. However, sometimes it is also disadvantage, as some of the objects are not revealed as they are covered inside shadow.

7. Association:

Many objects are seen along with other objects. This property is called association. For example, vegetation next to water bodies. Beaches next to oceans etc.

An interpreter looks for the above 7 elements while interpreting the photograph or image.

Image interpretation is a deductive process. It starts with a random opinion about an object in the image, and concludes with a decision about the same object.

The accuracy of image interpretation depends on several factors such as what is the scale of photograph, which spectral band is being used, how good and experienced the interpreter is? etc.

How much difficult is Image Interpretation:

Image interpretation is a complex process. It depends on scale of photograph, experience of interpreter, terrain conditions, objects, spectral band etc. In reality objects are observed in a 3-Dimensional way. However, in photographs all objects are flat and 2-Dimensional. Also, objects are seen with unnatural and unconventional backgrounds. Hence, it becomes difficult to observe the objects in the photographs.

However, by making use of tools such as stereoscopes, GIS etc., this process can become less difficult.

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