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Mastering Color Balance in Astrophotography: Tips for Processing LRGB & HaRGB Images

Learn essential techniques to achieve precise color balance in deep sky images. Explore LRGB methodology, correct hue shifts, enhance with Hydrogen Alpha data, and create stunning nebula images. Understand how to maintain G2V balance while adding Luminance data.

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Mastering Color Balance in Astrophotography: Tips for Processing LRGB & HaRGB Images

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

  2. Introduction • With Digital Imaging as the mainstay for astrophotograpy today, color balance remains an elusive target. • Here we will discuss key points on locking in accurate color balance for Deep Sky Images that use LRGB methodology. • Our topics will include: • Setting a reference for our gray scale • Understanding the LRGB hue and saturation shift • Correcting the shift in LRGB images • Understanding the Hydrogen Alpha contribution to an image • The role of Hydrogen Beta in the final color of nebula • 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 • Some math details – Why the shift? • Conversion to Lab starts with RGB -> CIE XYZ space then to Lab. • Conversion math reveals a coupling of G and L • “Salmon Pink” is light red + a bit of green added • Increasing L in value in conversion elevates G • 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? • For Emission Nebula can be 85% of photons • But - H-alpha is very close to the near IR band = 70% total • AND H-Beta is very close to the center of the Blue band = 15% • Hydrogen enhanced images are Simply Stunning, and provide additional Significant Structure. -How? • 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 • By adding H-alpha data we change the G2V balance of the star images • 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

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