Image Brightness & Contrast Adjustment

When an image is loaded into Jim, the brightness and contrast are automatically set to what Jim thinks will be a useful setting. To adjust the brightness & contrast, use the sliders to the right of the image display.

Unless you select a slice all contrast adjustments apply to the whole set of slices. If your computer is not particularly fast, and there are a lot of slices in the image, this can slow down contrast adjustment. To speed things up, select a slice before adjusting the contrast.

Intensity contrast sliders

  • The slider to the right adjusts the mapping between image intensity and the colour at the top of the colour mapping.
  • The slider to the left adjusts the mapping between image intensity and the colour at the bottom of the colour mapping.
  • The Button to set the contrast automatically button automatically adjusts the brightness and contrast, either for the selected slice (if slice-selected), or for the whole image.
  • The Button to link the intensity contrast button sets all image slices to the same contrast (the contrast of the selected slice).
  • If the Auto-Link contrast button looks like this: Contrast is linked across image sliders, then the contrast will automatically be linked across all slices, regardless of whether you have a slice selected. To adjust contrast on a slice-by-slice basis again, click it so it looks like this: Contrast is not linked across image slices.

If you wish to make fine adjustments to the contrast, click the Expand the intensity contrast range button to expand the available range. To make coarser adjustments again, click the Contract the intensity contrast range button.

If you find that the Link the intensity contrast across slices button is greyed-out, or you cannot adjust the sliders, this means that there is no selected slice, and the slices have different contrast, so Jim does not know which slice to adjust. Select a slice to re-activate these features. Then use the "Link" button to set the contrast the same for all slices if you wish.

CT Presets

You can set the brightness and contrast to fixed ranges suitable for X-Ray Computed Tomography images using the CT Intensity Presets menu under the View menu: CT presets on the View menu

Selecting one of the presets sets the contrast suitable for viewing one of the particular type of tissue listed. The numbers refer to the centre intensity and intensity range of the sliders, in Hounsfield Units.

You can also create your own CT presets, by selecting Create your own CT intensity preset,

This will bring up a dialog for you to enter the preset name, window centre and width (in Hounsfield Units):

Dialog to create a CT intensity presets

Click the Button to add a CT intensity preset button to create the new CT preset, which will then appear in the View menu:

CT intensity preset added to the View Menu