There are a number of ways to create color images with MaxIm DL.  The most common, by far, are the RGB method and the LRGB method.  Most CCD cameras have color wheels which allow you to take images through Red, Green, Blue, or Clear filters.  By combining the red, green, and blue images it is possible to make a full-color image.  This technique is called RGB imaging.  Taking a fourth image either through the clear filter or through a narrowband filter (such as a Hydrogen-Alpha filter) and then combining this Luminance image with the RGB creates an LRGB image.

RGB Images

Open the files you wish to use for color combining.  There should be one red, one green, and one blue file. 

Tip:  Try reducing the noise as much as possible by combining multiple exposures through each filter (see previous section on combining).  In this example each color component file is a median combine of three individual exposures through each filter (a total of nine separate exposures).

Each individual color component image is black and white.  Only after you have combined the files will they appear in color.

Above:  From top to bottom, red, green, and blue images of the Whirlpool Galaxy.  Notice there are subtle differences between the images and that the blue image is brightest due to the fact that much of the starlight from this galaxy is blue. 

Note:  Nebulas tend to show the biggest difference between color components, since they emit much of their light in red.  A red exposure of the Orion Nebula, for example, shows much more nebulosity than an equivalent blue exposure.  An extreme example is the Horsehead Nebula, easily seen in red light, but almost invisible in blue!

Select Color > Combine Color or click the Combine Color button on the toolbar (the leftmost button below).

The Combine Color window will open.  Select RGB under Conversion type.  In the Red, Green, and Blue pull-down menus select the appropriate files for each color.  In the Preview Image window you will likely see an unsettling rainbow effect in your image (shown below).  Don't worry, you just need to align the files!

Click on Align.  This opens the Align window, allowing you to register the files with each other.  Auto - star matching usually works just fine for Align Mode.  Click OK to align the files and return to the Combine Color window.  There should now be a more reasonable-looking image in the Preview Image window.

For now, leave the Output settings each at 1.  Click OK.

Above:  The result of the RGB color combine.

From here on out everything is pretty subjective as to the appearance of the image.  Often some color balancing is necessary when the Output settings are left at 1.  The above image looks perhaps a bit too green, like it needs a little more blue.

Select Color > Color Balance to open the Color Balance window.  It doesn't take much adjustment, so start subtle.  Here the blue has been upped 10%, from 100% to 110%.

Click OK to see the result.

That seems better, but feel free to play around to get the results you like best.

Alternatively, you can adjust the colors but changing the Output weights in the Color Combine window.  This adjusts the weight of each color to compensate for the varying sensitivity of the CCD chip in different colors.  (See the Color Theory page for more details on determining the correct RGB weights.)  For example, the SBIG ST-10XME camera used for this image has an RGB ratio of 1.3:1.0:1.8, meaning the red and blue channels need to be weighted 1.3x and 1.8x, respectively, that of the green channel.

Above:  Adjusting the Output settings for a 1.3:1.0:1.8 RGB ratio.

This results in the proper colors without the need for the Color Balance adjustments.

LRGB Images

The same techniques are used for LRGB images except that a fourth, Luminance, image must be opened.  Select LRGB in the Combine Color window under Conversion Type, and select the appropriate images from the pull-down menus.

Typically Luminance Weight is left at 100%.  Click OK to see the results.

Using Binned Color Files

Shooting images through color filters decreases sensitivity and requires longer exposure times.  By binning the pixels in a CCD camera, sensitivity is increased, resulting in shorter exposures, but resolution is lost.  If a high-resolution image is taken through a clear filter (maximizing exposure while retaining sensitivity), this image can then be combined with low-resolution, binned color images using the LRGB method.  Even though the color files have less resolution, the human eye receives its spatial information from the luminance portion of the image, not the color, therefore the image appears sharp.

Begin by opening the color files.  These need to be resized to match the size of the full-resolution Luminance image.  Select Process > Resize.  Click on No Constraint and change the New Image Size width and height to match the full-res image.  In this example, the color image was binned 3x3 and so was enlarge 3 times to match the unbinned luminance file.

Tip:  If your color images are binned 2x2, simply select Process > Double Size to convert them to the size of a 1x1 file.

Click OK.  The resized image will appear very pixelated.  This is okay because the luminance file will eliminate this.

Open the full-resolution luminance image:

Select Color > Combine Color, set LRGB under Conversion Type, select the appropriate files from each pull-down menu (Red, Green, Blue, and Luminance).  Click Align to register the image files, Click OK in the Align window and OK in the Combine Color window.

Note:  MaxIm DL sometimes has a hard time Auto Star Matching binned and resized files.  You may have to select another method such as Manual 2 star.  In this mode you click on the same star in each image to register the files.

Above:  An LRGB image using a full-resolution luminance image and 3x3 binned red, green, and blue images.

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