LRGB TECHNIQUE - TREATMENT WITH PHOTOSHOP AND PIXINSIGHT

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Note 1 - Open with Fit Liberator

If your images are in FIT (monochrome), Photoshop does not support this format. The software FIT Liberator can be used to open this type of file with Photoshop. I recommend you to use it because it allows you to open the images while keeping all the values ​​of the histogram of the image in both the lightest and darkest shades, thus ensuring that the background of the image is sky will not be "blocked" and that the brightest stars will not be overexposed. Personally I always open the image by applying the calibration Strech Function à ArcSinH (x),with a Self-scaling and making sure that the slider for the brightest values ​​in the histogram is greater than these (to the right) and that of the darker values ​​is less than these values ​​(to the left) as shown in the following image:

Note 2- Black and White point adjustment

If there is a gradient in the image, perform treatment # 1. Then, apply treatment # 2 in the following link:

Processing deep sky images

Note 3- Assembling the RGB image

  1. With Photoshop, open files your image Rouge.tif, Vert.tif and Bleu.tif
  2. We have to choose an image as a basis for our work. Let's use the Red image considering that the Green or Blue image could also be used. Click on the picture Red.tif and convert it to RGB by selecting Image | Fashion | RGB colors.
  3. Click on the picture Vert.tif to make it active.  Selection | Select all and then Edition | Copy
  4. Click on the picture Red.tif to make it active
  5. Open the window Layers and click on the Green Layer to make it active only:
  7. Paste the image Vert.tif in the green layer by selecting Edition | To stick on
  8. Repeat procedures 3 to 6 for the image Blue.tif. 
  9. Make all layers active by activating the eye for each one. From this moment we have an RGB composite image
  10. Save Red.tif in .tif format and give it the name Your name RGB.tif
  11. Close images Green.tif et Blue.tif

Note 4- Work done with curves

Apply treatment # 3 in the following link:

Processing deep sky images

Note 5- Color balance using curves

Click on this link.

Note 6- Luminance and RGB assembly

Click on this link and go to section Joining the Luminance image with the RGB color image.

Note 7- Other treatments

Consult the sections Processing deep sky images et Advanced treatments (consult the submenus) to see other treatments to improve the image. It can be a matter of removing imperfections in the image, making unsightly colors disappear from the sky background, removing noise from the sky background, etc.

Note 8- Increase image sharpness

Apply treatment # 13 in the following link:

Processing deep sky images

 

Richard Beauregard

Sky Astro - CCD

Revised 2021/05/03