To non-destructively brighten only the eyes of a subject in a photograph without affecting their skin or other elements, which on-device tool is most effective?

The most effective on-device tool for non-destructively brightening only the eyes of a subject without affecting their skin or other elements is an Adjustment Layer used in conjunction with a Layer Mask. This method ensures precise control and maintains the integrity of the original image data.

Non-destructive editing refers to making changes to an image without permanently altering its original pixel information. This allows for modifications to be easily undone, refined, or completely removed at any time without damaging the base image.

An Adjustment Layer is a special type of layer in image editing software that applies tonal and color adjustments (such as brightness, contrast, or color balance) to the layers beneath it without directly changing their pixel data. For brightening, a Curves Adjustment Layer or an Exposure Adjustment Layer is typically used. A Curves Adjustment Layer provides highly precise control over the image's tonal ranges, including highlights, midtones, and shadows, making it ideal for targeted brightening with fine-tuned adjustments. An Exposure Adjustment Layer offers a more straightforward way to increase overall brightness.

A Layer Mask is a grayscale image attached to a layer or an Adjustment Layer that controls the visibility or application of that layer's effect. White areas on the mask fully reveal the layer's effect, black areas completely conceal it, and shades of gray apply the effect partially. This is the crucial component for isolating the brightening effect exclusively to the eyes.

To achieve the specific result, one would first create an Adjustment Layer (such as a Curves or Exposure layer) and apply a brightening adjustment that, initially, would affect the entire image. Next, the associated Layer Mask is typically filled with black, which completely hides the brightening effect from the entire image. Then, using a soft-edged brush, one would paint with white directly onto the Layer Mask over the specific areas of the eyes that require brightening. This process precisely reveals the brightening effect only where white is painted on the mask, leaving all other elements, including the skin, completely unaffected. The non-destructive nature of this method allows for easy refinement of the mask by painting with black to remove the effect or with shades of gray to lessen it, ensuring perfect isolation of the desired adjustment.