Brightness, Contrast and Gamma

Brightness, Contrast and Gamma

Brightness, Contrast and Gamma

When dealing with monochrome images of fluorescently labeled cells, we need to understand and consider the differences between contrast, brightness and gamma. Most programs for viewing these images have controls that allow us to adjust these settings to our preference, so it helps to know a little about what contrast brightness and gamma actually mean to the overall presentation of the image. Here is an image displayed in the process section of the LAS software.

In the following images, the right hand side of the image is the before adjustment, and the left hand side is the after adjustment


Settings as the image was acquired


Note that there are sliders for Brightness, Contrast and Gamma. Brightness is the easiest of the three functions. It is simply a linear conversion of the measured image intensity to display intensity. Adjusting the slider affects each pixel the same way in a linear fashion.

Brightness increased


Contrast is the ratio of the brightest spot to the darkest spot in the image. It affects the range of the displayed image. Contrast is how dark to how light something is. Contrast adjustment is useful when you want to concentrate on something with detail but a small range of intensity. The downside to adjusting contrast is that if the adjustment gets pushed too far, the white level and black level get crushed and everything blends together. There is black and there is white, and there is no shading in between.

Contrast increased


Gamma works with the relationship of dark to light. An unadjusted gamma is a straight line between dark and light with a slope of 1. As you raise the gamma level above 1 you make the darker areas of the image darker. Lower the gamma below 1 and you make the darker areas of the image lighter. The gamma adjustment is a non-linear adjustment.

Gamma value reduced


Here is a Wikipedia article on Gamma.


An important side note about these functions. In the Leica LAS software, as in most imaging software, these functions are affecting the display of the image only, not the underlying image data. However, it is always a good practice to work on copies of your raw data and to have an unaltered copy of your data saved elsewhere just in case the software function you are working with does change the underlying numbers.


If you are adjusting these functions in the Leica software to bring out some detail in the image and you wish to store this, the export function will store your image with the enhancements. Be sure to use a different name.