Tips for Processing LRGB and Ha RGB Images
Tips for Processing LRGB and Ha. RGB Images: Getting the Color Right! By Chris Schur
Introduction n 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: n n n 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
How the Eye Perceives Color
Setting the Reference: The Sun Kitt Peak Solar Observatory
An actual G 2 V Calibration
Sample G 2 V Calibrated Image: M 3
Sample G 2 V Calibrated Image: M 81
Ha/L RGB Hue Shifts
LRGB Images: The Color Shift Problem: Salmon Pinks
Lab image details n Some math details – Why the shift? n n n 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
Correcting the Hue Shift
Next, Correct the Saturation
The Final Comparison
The Final Result:
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 AND H-Beta is very close to the center of the Blue band = 15% n n Hydrogen enhanced images are Simply Stunning, and provide additional Significant Structure. -How? n We then add it to the closest wavelengths: RED, BLUE.
Emission Nebula: The Process of adding Hydrogen Data – How NOT to do it…
Star Color distortion By adding H-alpha data we change the G 2 V balance of the star images n We can maintain the balance by combining Hydrogen data frame with the original R & B frame using Lighten. n
Restoring G 2 V balance with Lighten
Second Example: M 16 in Serpens
Final Discussion § § Understanding how adding additional Luminance data will affect the entire Lab Color Scheme Tastefully adding Hydrogen data into RGB images while retaining G 2 V balance is possible
- Slides: 20