SPOT 4.1 Basic and Advanced Software Manual for SPOT Insight ...

Ch. 5 – Preparing to Take a PictureWhen the bright areas of these types of images are correctly exposed, the darker areas can be so dark thatthey are in effect invisible. Gamma Adjust can remedy this problem. The figures below illustrate theeffect of a gamma adjust on a fluorescent image. The image on the left is the original image prior to thegamma adjust. The image on the right has been gamma adjusted to a value of 1.75. In this instance, thegamma adjustment results in a better display of detail by lightening the darker areas without burning outbright areas or lightening black areas:Fluorescence image, no gamma adjustment Fluorescence image, gamma adjusted to 1.75Figure 5- 4: Effects of Gamma Adjustment on a Fluorescence ImageGamma adjustment corrects an image by creating a new version of the original. To create the new image,the Gamma Adjust function reassigns the RGB values of each pixel in the image according to the curve inthe graph at right. This graphfull scaledemonstrates the basic principles ofgamma adjustment:• Black (pixel value = 0) remainsblack at all gamma values.• White (pixel value = full scale)remains white at all gamma values.• Gamma values greater than one liftthe darker areas of the originalimage into the brighter areas of thenew image.• A gamma curve is smooth - there areno unexpected jumps or cutoffs.This means that when viewing agamma-adjusted image, you will beable to see the details (intensitydifferences) in both the black andwhite areas of the image.0Pixel Value - New Imagegamma > 1gamma = 1gamma < 1full scaleOn the Image Setup window, you can0Pixel Value - Original Imagespecify whether or not to automaticallyapply gamma adjustment to an image capture. Figure 5- 5: Gamma CurveThis process works well if you know in advancewhich gamma value works well for a specific class of images. If you are not certain of the best gammavalue, you can acquire non-gamma adjusted images, and then use the HSL, HSV, or RGB gamma adjustoptions on the Edit menu and experiment with the gamma adjust options to find an optimal value. Refer toChapter 8 - Viewing, Editing, and Annotating Images for details on using the gamma adjust options.108 User Guide to the SPOT Insight Camera