Once we have the image loaded into the editor, with Raw Thereapee you have the choice of starting off from a neutral position or with the camera settings applied. This is very much up to how you prefer to process your images from the RAW file .
I generally start from the point of having the camera settings applied as this supplies lens correction, chromatic correction ( Not applicable if using legacy lenses ) and other underlying parameters such as image tone, sharpness & noise settings.
I first start with dropping the exposure compensation close to the 1.00 position. This takes out a lot of the wash effect and leaves a more subdued look to the image. ( Flat)
Following the previous step I will change the black levels to give the background sky and foreground shadow a darker look. This step is very subjective and is done entirely to taste. Once I have settled on a level I like I move on down the controls to the lightness control. You will notice that the highlight settings arent changed as there are no major highlights in the image.
Bear in mind that the night sky is not truly black even when viewed from a really dark-sky site. There is always a small amount of light wash in the background sky caused by atmospheric refraction and starlight. An inky black sky can be a nice tone to achieve for visual impact but needs to be done with care or fine detail can be lost in the process.
Lift the lightness value until the level of detail is about where you would like it to be. At this point you may want to adjust the contrast, but do it in small steps as it acts very quickly. At this point I select the saturation tool and push the saturation a higher, somewhere around +50 brings an increase in warmth and tonality.
The second set of controls alongside the exposure controls are the noise reduction tools. I dont change anything here at this point as I want to make all changes prior to any NR I may need. The next set of controls are for colour and vibrancy and colour temperature.
At this point I will change colour temperature. In the image above I opted for a cooler and slightly blue tone. Adjust to suit you preference.
Next I enable Vibrance controls an use the pastel saturation tone slider. You can separate the pastel & saturation controls by clicking the Link Pastel & Saturated tones. Adjusting the pastel tones and the saturation helps bring out the colour in the stars and nebulae.
I generally dont use any of the other controls in the colour menu for astrophotography but that shouldn’t stop you from experimenting in case there is something you may find that enhances your images further. For the sake of this set of tutorials we will limit ourselves to the basic controls.
Once you have everything the way you want its time to check the noise level
Toggle the before and after control to split screen your image. Use the mouse scroll wheel to zoom in to view the noise in the image and adjust until the image exhibits a pleasant smoothness with out losing detail. If you want to use more control here select the Luminance Curve drop-down toggle and switch to linear. You now have a more comprehensive set of controls at your disposal. Adjust these controls and compare the results in the split screen. Scrolling forward & back with the mouse gives you the opportunity to view wider areas for comparison.
Once you are satisfied with all the changes you have made we need to save the profile of the image as this is the base image to edit all the others.
At the top right of the editor is the processing profiles section. Select the hard-drive icon immediately to the right of the folder icon. This will bring up a save request box. Rename the current file to any name you wish and save the file. The editing profile is now saved.
Now we must save the image we have edited. To do this select the small hard-drive icon at the bottom left of your screen, adjacent to the preferences control, and save your file.
Important note: Save your images as 16 bit Tiff to retain the data that the RAW contained. This yields much better stacked images.
The following steps need to be repeated for all the remaining images. Toggle the upper sidebar to reveal the images you have loaded in the editor. Your first image will show the changes. Double click to load the next image and select your editing profile from the folder in the processing profile menu. Select your previously saved profile and click open. Your image has now been edited the same as your base image. Save the image and repeat for all the images. For larger image series a batch process may be a good option, and will be the subject of a further tutorial. The one draw back to batch editing is the inability to use a pre saved profile, hence the method outlined above. I will investigate this further as it seems odd that this option inst readily available in the batch edit process.
And thats it, all done and ready for stacking.