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Tips for Processing LRGB and HaRGB Images: Getting the C o l o r Right!

Tips for Processing LRGB and HaRGB Images: Getting the C o l o r Right!. By Chris Schur. Introduction. With Digital Imaging as the mainstay for astrophotograpy today, color balance remains an elusive target.

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Tips for Processing LRGB and HaRGB Images: Getting the C o l o r Right!

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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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