What is a filter used for in image manipulation programs?

A filter in image manipulation programs is employed primarily to apply special effects to images. Filters can alter the texture, color balance, contrast, and overall aesthetics of an image, allowing designers and photographers to create specific moods or artistic styles. They can add effects like blurring, sharpening, color adjustments, and textures, helping to transform the visual presentation significantly.

The other options pertain to functions that filters do not encompass. For instance, enhancing brightness levels alone refers specifically to adjustments in exposure rather than a broader application of artistic effects. Saving images in a different format pertains to file management and is unrelated to the application of visual effects. Resizing images without changing quality typically involves specific algorithms, not filters, which focus on altering the artistic characteristics of an image rather than adjusting its dimensions. Thus, the primary purpose of filters is clearly aligned with applying special visual effects, making that the correct response.