When color grading a night cityscape, what is the technical purpose of using HSL adjustments to fine-tune the color of specific light sources, such as neon signs?

HSL adjustments refer to the manipulation of Hue, Saturation, and Luminance within specific color ranges of an image. Hue defines the pure color itself, such as red or blue. Saturation determines the intensity or purity of that color, ranging from dull to vivid. Luminance controls the brightness or darkness of that color. The technical purpose of using HSL adjustments to fine-tune the color of specific light sources, such as neon signs in a night cityscape, is to precisely and independently control their visual characteristics without affecting other elements in the scene. This granular control allows for several critical functions. First, it enables correction of color shifts or inaccuracies within individual light sources that may result from camera capture or environmental factors. For example, a neon sign intended to be a specific blue can be precisely adjusted to that blue, rectifying any unintended purple or cyan cast, without altering other blue tones present in the sky or other lights. Second, HSL adjustments facilitate enhancement and separation by making specific light sources more vibrant, brighter, or shifting their hue to stand out clearly from similar colors in the background or adjacent lights. This means a red neon sign can have its saturation or luminance increased to pop more effectively without oversaturating or overbrightening other red objects in the image. Third, it allows for stylization, where the colorist can align the colors of targeted light sources with a specific aesthetic or mood for the entire scene. This could involve subtly shifting a green neon sign's hue to a cooler or warmer green to match a desired color palette, while preserving the color integrity of other green elements like foliage. This highly selective control ensures that the intended visual impact and artistic vision for each specific light source are achieved, maintaining realism or delivering a specific stylistic look without introducing unwanted global color changes.