1. Tips for Processing LRGB and HaRGB Images: Getting the Color Right! By Chris Schur

2. Introduction n With Digital Imaging as the mainstay for astrophotograpy today, color balance remains an elusive target. n Here we will discuss key points on locking in accurate color balance for Deep Sky Images that use LRGB methodology. n Our topics will include: n Setting a reference for our gray scale n Understanding the LRGB hue and saturation shift n Correcting the shift in LRGB images n Understanding the Hydrogen Alpha contribution to an image n The role of Hydrogen Beta in the final color of nebula n Tactfully combining Hydrogen and RGB data for balanced images

3. How the Eye Perceives Color

4. Setting the Reference: The Sun Kitt Peak Solar Observatory

5. An actual G2V Calibration

6. Sample G2V Calibrated Image: M3

7. Sample G2V Calibrated Image: M81

8. Ha/L RGB Hue Shifts

9. LRGB Images: The Color Shift Problem: Salmon Pinks

10. Lab image details n Some math details – Why the shift? n Conversion to Lab starts with RGB -> CIE XYZ space then to Lab. n Conversion math reveals a coupling of G and L n “ Salmon Pink ” is light red + a bit of green added n Increasing L in value in conversion elevates G n So by adding additional L, we shift reds to salmon

11. Correcting the Hue Shift

12. Next, Correct the Saturation

13. The Final Comparison

14. The Final Result:

15. Adding H-Alpha Data to the Image: -Why? n For Emission Nebula can be 85% of photons n But - H-alpha is very close to the near IR band = 70% total n AND H-Beta is very close to the center of the Blue band = 15% n Hydrogen enhanced images are Simply Stunning, and provide additional Significant Structure. -How? n We then add it to the closest wavelengths: RED, BLUE.

16. Emission Nebula: The Process of adding Hydrogen Data – How NOT to do it …

17. Star Color distortion n By adding H-alpha data we change the G2V balance of the star images n We can maintain the balance by combining Hydrogen data frame with the original R & B frame using Lighten.

18. Restoring G2V balance with Lighten

19. Second Example: M16 in Serpens

20. Final Discussion  Understanding how adding additional Luminance data will affect the entire Lab Color Scheme  Tastefully adding Hydrogen data into RGB images while retaining G2V balance is possible