Enhance underexposed underwater photo

[BLR]

Please suggest enhancements to this underexposed underwater photo. It seems like adjustments I try to make just magnify the jpeg artifacts. Should I give up on this old jpeg scan, find the slide, and rescan it in tiff format?

In case you're curious:
Grand Cayman Island, BWI about 1995
The tunnel started about 40 ft. and exited the wall at about 80 ft.
There's about 4,000 ft. of water below the diver.
Minolta X-700, Minolta 20 mm f/2.8 MD lens
Kodachrome 64
Ikelite housing & Substrobe 100 strobe (shot with available light, because strobe's battery died during dive)

Thanks,

Barry

[lurch]

Should I give up on this old jpeg scan, find the slide, and rescan it in tiff format?

That's what I'd do. It'll make a world of difference in ease of correction and in the quality of the outcome.

[DCobb]

Not sure what is to be enhanced in this type of photo? Made a little change. Original on the left.

dc

[mistermonday]

Your scan may be OK unless you overcompressed it when you saved it as a jpg. Make sure your jpg setting is high (11 or 12). Saving the file as a TIF is fine but it will not resolve the problem.
The shadow areas are almost pure black and have no detail. Therefore all you will accomplish by lightening them is to add noise and make them a muddy gray. You might be better off making the blue less intense and brighten the rocks that have some detail. Then isolate the diver and apply a curve to put more contrast just on him. Finally shift the hue of the rocks that have detail.
BTW, the image you uploaded was 24 x28 in @ 72dpi, which is huge for the 100KB limit and meant you really had to overcompress it. In future yu would be much better to size it to approx 5 x7 or 6 x 8 @ 72 dpi and save it at a higher quality jpg setting.
Regards, Murray

[lurch]

Murray has given you good advice. I fiddled with your image a bit last night - changing to a lossless format won't solve your problem, which is missing information more than jpeg artifact. The red channel is essentially pure black because there's virtually no red light at that depth (except what might have been provided by your dead strobe). In the deep shadows the green and blue aren't much better either. A re-scan at 16 bits per channel might give you a little more info to play with. You could also play around with channel blending to build a new red channel or a good luminosity mask.

[Juergen D]

Here is my attempt. I thought it may be good to get away from all that blue, shifting into green some. Added a red Photo Filter (10%) and sharpened. The diver was treated separately with a Curves adjustment.

Juergen

[Gary Richardson]

Not sure quite what you're aiming for here.

As per all underwater shots the red channel was practically non existent, so I replaced it with the green, then adjusted levels on each channel for best effect.

Brightened whole pic a touch.

[des151]

Hi Barry,
Thought I'd dive in and give this a try.
Ray