by
MichelB » Fri Jun 05, 2009 10:50 am
Yes, red flowers are problematic, but very often that's also the case for yellow and orange. If you have a look at the color histogram, in CS, Elements or ACR, you'll generally find that the red histogram is squeezed on the right side, meaning that a lot of the red pixels have the maximum value whereas the blue and green are squeezed on the left, with many pixels with minimum value. A saturated color may be defined as being a pure hue, meaning: without any amount of white or gray. That means a saturated color has only one (red, for example) or two RGB components (red and green for yellow, for example). One or two components are missing completely. A saturated red may have some green or blue component, accounting for a slight change in hue.
Let's examine different cases:
- The worst one: A lot of pixels have both maximum red value and no blue, no green. Those pixels will have a flat pure red look, without any difference in hue or luminosity.
- Most reds don't reach the maximum, but there is no blue or green. The result will be a pure saturated red hue look, but with differences in luminosity, which may keep some texture.
- Many red pixels reach the maximum, but either blue or green pixels are present. This will produce a difference in hue and luminosity, keeping some texture and tone differences. The problem of the maximum in red values is that hue and tone will be inaccurate.
Many red flowers are naturally saturated, with either blue or green components missing, or both. To avoid the worst case above, the obvious way would be to underexpose and compensate in editing. The risk is to lose data mainly in the blue component.
To get the best results with red flowers, besides slight underexposure:
- shoot raw if possible. Pay particular attention to color temperature and exposure to avoid red clipping and loss of blue. Be prudent with contrast, saturation or vibrance, watching the histogram. For further levels or hue/sat adjustments in CS/PSE, stay in 16 bits to begin with.
- if you shoot jpeg, be careful to use conservative settings in your camera settings, don't boost saturation or contrast and watch white balance.
Finally, there will be cases where you'll have to compensate for clipped reds (a lot of red pixels at maxium value). If there is detail in the blue or green channel, you may recover those channels and use them as overlays (soft light or overaly blending mode) to give back texture.