Color correction in standard images is mainly based on controlling the interaction of illuminant and reflectance and often results in a compensation of actual chromatic casts with respect to a chosen reference illuminant. Primary reference illuminants come from our reference star, the sun, whose color characteristics are of G2V star class. Visually, color correction in standard images allows us to obtain scene colors more pleasant and closer to our everyday experience. Quality of color is usually intended to please the vision system of the observer, that looks at the picture using the powerful mechanisms of visual color and contrast adjustment (color constancy), a very different tool with respect to a camera. In astrophotography this basic principle does not apply: the illuminants of the many different stars or emission nebulae are the only information we detect, while the only reflectance involved (not considering Solar System planets) is originated by dust particles producing the so called reflection nebulae. Thus, what is the meaning and the goal of color correction in astrophotography? In this paper, we try to present to the reader some points of discussion about this broad question.
Blue sky color is an important memory color for outdoor photography. Reproducing it pleasingly is essential for preferred color reproduction of photographic images. A simple approach for enhancing blue sky color is to detect blue sky colors and then enhance all sky blue pixels regardless of their object types. However, this method has a negative effect for modifying blue colors of non-sky objects. In this paper, we present an improved method for detecting the sky region of images captured with digital cameras, followed with a method to enhance blue sky colors for visually pleasing results. Treatment of white sky colors (overexposed sky colors and white clouds) and sunset and sunrise warm sky colors are presented as well.