Question 11

Do you know your image enhancements?

Visual interpretation of images often make use of image enhancement to make certain features more prominent and simpler to recognize. But the specific enhancement to be used depends on the feature to be interpreted and the nature of the imagery.

Original Image

Text Version - Original

Original

This illustration shows an image of Truro (N.S.) in grey tones and acquired by LANDSAT-TM. We can see cropland, rivers, forest and urban areas. The image lacks contrast voluntarily.

Which enhanced image below (A, B, C or D) is the result of:

1. contrast stretch enhancement

2. high pass filter enhancement

3. intensity slicing enhancement

A

Text Version - Item A

Item A

This illustration shows the original image after contrast enhancement. This type of enhancement produces an image that emphasizes areas of fine spatial detail.

B

Text Version - Item B

Item B

This illustration shows the original image after contrast enhancement. Grey tones are stretched in this type of enhancement; dark areas are even darker, and bright areas brighter.

C

Text Version - Item C

Item C

This illustration shows the original image after contrast enhancement.

D

Text Version - Item D

Item D

This illustration shows the original image after contrast enhancement The image is in color.

Hint for Contrast Stretch:

From the CCRS Glossary:
"A process in which the range of brightness levels of an image is expanded to use the full brightness range of the recording film or display device."
The "stretched" image shows dark areas even darker, and bright areas brighter.

Hint for High Pass Filter:

From the CCRS Glossary:
"A type of spatial filter that uses a convolution filter to produce an image that emphasizes areas of fine spatial detail (e.g. edges)."
The enhanced image should look sharper/crisper, with better defined lines.

Hint for Intensity Slicing:

This process involves substantially reducing or grouping the number of discrete grey levels from (say) 256 to 16. The resulting grey levels can be displayed as unique shades of grey or as discrete colours.

Image Information

Truro, Nova Scotia, Landsat TM