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Thread: Digital image exposure adjustment

  1. #1

    Digital image exposure adjustment

    I'm hoping for some suggestions for a small project:

    I have some photos taken during the recent annular solar eclipse, of the surrounding land, as the Sun was progressively covered.
    Since they were taken with my iPhone, the images all look equally exposed, as expected, but the exposure times from the EXIF data vary broadly with the light level, from 1/1770 second to 1/96 second, f/2.8, ISO 64.

    How can I "reverse adjust" the images, to approximate the effective exposure, as if they were all taken at one shutter speed, say close to the shortest, 1/1770?

    I can easily enough use one or another tool to darken the images, but I'd like to do it quantitatively...

    Dave

  2. #2

    Digital image exposure adjustment

    I use Adobe Lightroom for most of my photo work and it allows you to adjust exposures by stops, which would let you do it quantitatively. I"m not sure which other tools might have a similar function.

  3. #3

    Digital image exposure adjustment

    Quote Originally Posted by 2123
    I use Adobe Lightroom for most of my photo work and it allows you to adjust exposures by stops, which would let you do it quantitatively. I"m not sure which other tools might have a similar function.
    Yes - "by stops" would be perfect.
    I'll check it out, thanks!

  4. #4

    Digital image exposure adjustment

    I asked a coworker if he had a copy of Lightroom; he does, but also recommended the open source RawTherapee
    I downloaded that, and it works great.

    It *does* prefer a 64-bit machine, with lots of RAM, though!
    As the developers warned, it crashed several times, as I processed ten 1.4┬▒MB images, running on a relatively small 32-bit PC under Windows XP.

    I'll put together a montage of the auto-exposed and compensated images and post here.
    It's amazing how the eye (and automatic exposure) lies to us about the actual light level...

    Dave

  5. #5

    Digital image exposure adjustment

    Some otherwise uninteresting snapshots taken with an iPhone 3GS during the Anular Solar Eclipse of 5/20/2012.
    On the left, automatic exposures,taken several minutes apart, as the Sun was gradually covered by the Moon.
    On the right, the same images, adjusted digitally to (de-)compensate for the gradually increased exposure times.

    Dave Attached files

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