Generally, yes: higher ISO settings tend to reduce dynamic range and can also reduce color discrimination, while making noise more visible. On cameras like the Pentax K-x, measurements show dynamic range drops noticeably at very high ISO, and color performance also declines.

That said, the root issue is usually limited light. Raising ISO doesn’t create noise by itself so much as it allows a usable exposure when there isn’t enough light for a lower ISO at your chosen shutter speed and aperture. In practice, using a higher ISO is often better than underexposing at a low ISO and then brightening later.

So Auto ISO isn’t automatically “making images worse” — it’s a tradeoff. If Auto ISO lets the camera maintain a shutter speed or aperture you need, the result may be better overall than blur or missed focus. But if the camera reaches ISO 6400, expect less dynamic range, noisier shadows, and somewhat weaker color than at lower ISO.