Combining Bitmaps: Shadows, Midtones and Highlights
In previous lessons, we demonstrated methods for color balancing and contrast enhancement. As our eyes are particularly sensitive to changes in contrast (i.e., luminance changes) it is useful to segment three target areas for image improvement:
- Shadows
- Midtones
- Highlights
Common image processing functions that manipulate brightness and contrast affect all three segments simultaneously -- usually at the cost of degrading one segment for another. Significant improvement in image quality can be achieved by selectively manipulating shadows, midtones and highlights. Lets continue from the previous lesson (i.e., remapping colors) ...
- Select Enhance|Fix_UnderExposure.
- Select Levels,_Back_Fill method.
Use the default value detected for adjusting highlights. Highlights slider was set to "238". Adjust the Gamma slider to lighten more of the shadows; it is set to "105". Finally, adjust the Mask slider to "39" to avoid overexposure by blending some of the original highlights and midtones. The "white" of the eyes are now more visible; also, shadows around the eyes and cheekbones have been lightened.
By adjusting Highlights, brightness was improved from midtones and up. Adjusting the Gamma control boosted midtones and some shadows. Finally, the Mask slider tweaked the enhancement by combining some of the original highlights and midtones to avoid overcompesation effects. We can still do better in our pursuit of the "perfect picture".
- Select Enhance|Fix_Contrast_Levels.
- Select Optimize method.
The shadows could still be a bit darker and the highlights could take a little boost. Yet, we want to keep all modification to midtones. Using the Optimize method, the entire picture is remapped for maximum contrast -- i.e., it remaps to span the widest possible range between shadows and highlghts - affecting midtones in the process. The Mask control of the extended Optimize function, keeps existing midtones in variable amounts. Here we set it to "182". Viola! All modifications to midtones are kept, while maximizing shadows and highlights.
