Merge RGB Images

The Merge RGB Images command combines 3 separate images that contain red, green, blue channels to make an RGB color image.


This command uses 3 input images to produce 1 output image, which is the merged RGB image. Using the Image Tree controls in the dialog, the 3 input images may be selected from the same Image Set in one window or they may be selected from different windows. Each input image must not be an RGB image itself.

The Auto check box enables automatic merging after a parameter change so that you don't have to keep clicking the Merge button. If you want Mira to automatically update the merged image after you change a parameter, Check this item. if the Auto box is not checked, Mira does an update only when you click the [Merge] button.

Oftentimes you will choose new setting that give a poorer result. The [Revert] button recalls the set of values used in the most recent, prior merging and updates the preferences with them. This is an "undo" for the preferences but not for the merged image.

The critical determinant of the brightness, contrast, and color balance is the choice of theMin Value and Max Value levels in the 3 input images. As described below, Mira gives you 3 ways to set these values.

Using Min Value and Max Value

The Min Value and Max Value parameters control the placement of the "black point" and the "white point" in the luminance values of the input images. When merged into the output RGB image, all pixel values lower than the Min Value are assigned "black" and all pixels above Max Value are assigned "white". These values do not need to be the same for each of the images. Typically they may be different if the images have different background signal or inherently different contrast. The particular values you use affect the overall brightness of the RGB image as well as its contrast and color balance.

Beyond wild guessing, there are 3 ways to choose the Min Value andMax Value parameters:

Note that this is an interactive procedure and you can tune the preferences after each trial to home in on the best possible result. Simply adjust the parameters and re-Merge the images to get a new result.

Using the Lock Option

When you adjust the Min Value or Max Value, there are times when you want to set the values independently, and there are other times when you want them to change together. To make the entire column of values change when you change one of them, check the Lock check box in the appropriate column.

After merging, you can refine the color using simpler methods than Min Value and Max Value. You can finalize the brightness, contrast, and color balance using the palette stretching technique with the mouse or by making adjustments in the Palette Properties dialog.

Related Topics

RGB Image Commands, Merge LRGB Images