Microscopy Primer
Light and Color
Microscope Basics
Special Techniques
Digital Imaging
Confocal Microscopy
Live-Cell Imaging
Photomicrography
Microscopy Museum
Virtual Microscopy
Fluorescence
Web Resources
License Info
Image Use
Custom Photos
Partners
Site Info
Contact Us
Publications
Home

The Galleries:

Photo Gallery
Silicon Zoo
Pharmaceuticals
Chip Shots
Phytochemicals
DNA Gallery
Microscapes
Vitamins
Amino Acids
Birthstones
Religion Collection
Pesticides
BeerShots
Cocktail Collection
Screen Savers
Win Wallpaper
Mac Wallpaper
Movie Gallery

Image Contrast Adjustment

Nonlinear functions selectively expand contrast in one part of the brightness range by contracting contrast elsewhere. This can also be used to compensate for the characteristics of the acquisition device, which may be linear, logarithmic, or have some other response. These adjustments are best understood in terms of the transfer function. This interactive tutorial illustrates the nonlinear adjustment of the display transfer function for an image. In the tutorial, the slider changes the shape of the transfer function without shifting the midpoint or end points. Applying such changes to the individual RGB channels can produce color shifts, and so operating on the intensity only while leaving color alone is the preferred method.

The tutorial initializes with a randomly selected specimen imaged in the microscope appearing in the left-hand window entitled Specimen Image. The Choose A Specimen pull-down menu provides a selection of specimen images, in addition to the initial randomly chosen one. The histogram of the image is shown in the right-hand window along with the transfer function that plots the output or display pixel brightness for each original or stored pixel value. The Contrast Level slider controls the shape of that function. As this is adjusted, either by sliding it directly or by using the arrow buttons shown at either end, the histogram shifts, expands or contracts and the image display adjusts accordingly.

Clicking on the Grayscale Contrast button shows just the monochrome version of the image, with its corresponding histogram. Clicking on the HSI Contrast button shows the color version of the image, but the histogram still shows just the monochrome intensity and the slider adjustments of gain and brightness affect only the intensity and not the color values. Clicking on the RGB Contrast button allows the sliders to manipulate the individual color channels. Clicking on the Red, Green and/or Blue button selects which channels is being adjusted individually. Adjustments may be made sequentially, one channel at a time.

Contributing Authors

John C. Russ - Materials Science and Engineering Dept., North Carolina State University, Raleigh, North Carolina, 27695.

Matthew Parry-Hill, and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.


BACK TO INTRODUCTION TO DIGITAL IMAGE PROCESSING AND ANALYSIS

BACK TO MICROSCOPY PRIMER HOME

Questions or comments? Send us an email.
© 1998-2009 by Michael W. Davidson, John Russ, Olympus America Inc., and The Florida State University. All Rights Reserved. No images, graphics, scripts, or applets may be reproduced or used in any manner without permission from the copyright holders. Use of this website means you agree to all of the Legal Terms and Conditions set forth by the owners.
This website is maintained by our
Graphics & Web Programming Team
in collaboration with Optical Microscopy at the
National High Magnetic Field Laboratory.
Last modification: Monday, Sep 12, 2016 at 02:07 PM
Access Count Since July 20, 2006: 6158
For more information on microscope manufacturers,
use the buttons below to navigate to their websites: