The Lagoon Nebula

This image is primarily red, so to give it the red color you need to stack more red frames than the others.  One mistake that is usually made is that when being asked to process the image a person tends to make the entire picture look more “normal” so that all parts of the nebula can be seen. This would be good if you were not going to stack the frames but if you do stack them it will look overexposed.

Depending on how long the exposure was, and how bright each frame is will determine what stretch function to use.  The one that seems to work best is Log form.  It does not make the image too bright and it gives room to adjust the image to make it look just right. 

One thing that can be overlooked is to put it into 8-bit form.  Standard for New Mexico skies imaging is 16-bit, but the Fits Liberator only works with images if the setting is changed. 

Before stacking the different frames, it is best to go to Filter, Noise, then Despeckle to get rid of bad data and spots in the imaging.  It may not be noticeable in one frame, but after being stacked it makes it look much cleaner. 

To stack the images just cut and paste the images on top of one another, then go to the bottom layer and change the name by double clicking it.  It will default to calling it “Layer 0” which is fine.  The reason to do this is to unlock the layer incase it needs to be moved to line up the different frames.  After that under the layers swatch is a pull down menu, which needs to be set to screen.  All layers should be set from normal to screen with the exception of the bottom layer, or “Layer 0”.  The easiest way to line them up is one layer at a time.  By clicking the eye next to the layer that is being worked with can change if it’s visible or not, so other layers can be moved easier.  Just be sure that the layer you want to move is highlighted or a different frame will be moved even more off center than it was.  Zooming in on a group of stars that stands out is an easy way to be sure that its lined up, then for fine tuning use the arrow keys to be precise to finish moving it. 

After all the layers are completely lined up go to Layer and Flatten Image.  This way once the green, blue, and luminance frames are done there are only four layers to work with. 

Making the green, blue, and luminance layers for the final image is the same as it was for the red.  The only minor change is the number of frames used.  The best for this particular object would be most images stacked in the red, followed by green and blue.  The fewest required stacked images are the luminance frames, as it tends to overexpose it, and lessen the color of the final product. 

Once all four are finished cut and paste the images on top of each other in the order blue on the bottom followed by green, red, and luminance.  Line them up the same as before by using the eye tool. 

One thing that may be useful is being able to change the opacity of each layer.  If you find that it looks over exposed, go to the layers swatch and find opacity and change it to the percentage that looks the best.  Just be sure not to change it too much on one layer as it may change the over all color of the image.

The next step is playing the action.  Select each layer individually and play the color action that corresponds to the color filter used on each frame.  For the luminance layer, the action has to be played manually.  Go to Layer, New Adjustment Layer, then click on the three different options Levels, Curves, and Hue/ Saturation.  It will ask you if you want to merge the action and be sure to click “don’t merge” so you can go back and adjust them to how you want.

It may be needed to adjust the opacity again to get the colors just right. The best layer to change the opacity for is the luminance layer so as to not loose some of the color.

To give the image that bright red color, the easiest way is to click levels under the red frame and adjust it.  One thing to be aware of is to not over adjust it so that the stars also turn red.

After the entire image is done, it’s useful to have a Photoshop available that does not have the Fits Liberator installed so the image can be fine tuned.  This allows starts to be whitened and spots to be removed much easier, so as to not have to go to each layer and change something.  For this particular image stars could be whitened to get rid of any red tint the levels action may have given it.