ISO comparison
The photo quality from the S4000 is OK; good enough for small prints and Web use, but questionable for anything else. Though the camera is capable of taking decent snapshots in bright lighting conditions, quality drops off noticeably between ISO 200 and ISO 400 with increased noise and softness. The noise wouldn't be so bad if it didn't cause inconsistencies with color. The noise reduction causes smeared details, and this smearing only gets worse at higher ISOs, making it a poor choice for low-light photos.
In Auto mode there's a Fixed Auto ISO option, letting you limit the camera to using a range between ISO 80-40 or ISO 80-800. I recommend using the 80-400 range whenever you're shooting in a mixed lighting environment and don't feel like switching ISO settings. The camera also seems to have problems focusing. Regardless of mode or even using the tap-to-focus feature, it really struggled to focus on subjects, causing me to refocus again and again before shooting.