HDR partial success

After I hacked some pink/purple LEDs into some Christmas light strings and wanted nice pictures, I faced the usual problems of photographing lit LEDs. The ones I wanted were from outdoors looking into a window at night, making it even a little more challenging.

My first pictures wouldn’t even let me try to use picturenaut – even with manual -2EV exposure, the LEDs were overexposed.  I remembered that CHDK on my little Canon SD600 provided some bracketing, and soon figured out how to use that, including the counterintuitive option of “+” for brackets with decreasing exposure.

The first set of brackets (left) looked very promising – from bright enough to see the window frame and curtains inside to one with the LEDs underexposed.  At 2/3 EV per shot it covered a little over 9 EV, and CHKDK put EXIF info in the images so picturenaut knew what the exposure differences were.  But the software couldn’t work enough magic to make a great picture.  I tried several combinations of the source images and played with most of the adjustments in the four post-processing tabs, but in the best I could come up with the pink LED was still pretty washed out, with the highlights near full white – just what I wanted to avoid.  (right)

Lauren made the excellent suggestion of trying during daylight to decrease the contrast with the background.  That produced pretty promising pictures of the LEDs with plastic diffusers, but the hack with a white card for the pink LED to light up was way too well lit by the daylight and again washed out.

Later, in twilight, I tried using spot metering on the LED of interest.  That helped a little.  I did another set of bracketed exposures (again about 9 EV), and for reasons I don’t understand, picturenaut was able to do considerably better with those.  It gave me something about like what it looked like to my eye.  Sorry about poor focus – I didn’t notice it until I was back inside with the tripod taken down.  I did a +0.4EV brighten on what it produced for the picture on the right.

I guess the biggest takeaway is to remember that CHKDK will let me get the low exposures I need for HDR to have a chance.  Next is that magic spoils us (or at least me).  After seeing what picturenaut could do, I’m now disappointed when it can’t create a storybook picture out of chaos.  Or maybe I just didn’t play with the knobs enough 🙂

This entry was posted in HDR. Bookmark the permalink.

One Response to HDR partial success

  1. Pingback: Hacking pink LEDs into Christmas lights | Jim's Projects

Leave a Reply

Your email address will not be published. Required fields are marked *