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Changing Exposure Info

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  • photo_two
    Member

    I was wondering when I modify the exposure on a raw file and save as jpeg is there a way to update the exif data so that the exposure info changes. Reason being another program i am using to process seems to use that information. I am basically trying to create an hdr by adjusting the exposure of the raw. Am I off base?

    Thanks for any info.

    Posted On April 6, 2009 - 03:14 PM (1 year ago) (Permalink to this post)

  • Sam Dring
    Moderator

    If, for example, you are using photomatix, you don't need to worry about the exif data.  The following extract may help:

    Open up your RAW file in your favorite RAW converter . Don't touch any of the settings except the Exposure slider (you can also fine tune white balance, sharpness, ... but thats covered elsewhere).
    Play around with the exposure slider. Move it to the left and see the image become darker. Watch your highlights and see how much information we can recover. Find out how low you need to go (but don't go much beyond 2 f-stops).
    It will depend on your camera how far you can push this.
    Remember the number (e.g. -2).
    Then move your slider to the right and see how much you can pull out of the shadows (without seing too much noise).
    Remember that number (e.g. 2).
    Subract the two numbers (2 - (-2) = 4).
    In our example we are going to cover a 4 f-stop range (thats about as far as this works on RAW files for most Canon Cameras I guess (I hear the new line has 14-bit analog to digital converters, so it may go further).
    Now divide those into n equal steps, not much larger then about 1 f-stop.
    In the example above this results in 5 images:
    (-2, -1, 0, 1, 2)

    Example2:
    Min = -1.6
    Max =  0.8
    Result = (-1.6, -0.8, 0, 0.8)

    Enter these numbers into the Exposure compensation box and convert one image for each (5 images in the first example). I usually save them as TIF files so I don't lose information to compression (until the very end when I save everything as JPG).

    Full tutrial at

    http://www.aguntherphotography.com/tutorials/raw-hdr-processing.html

    Posted On April 6, 2009 - 03:48 PM (1 year ago) (Permalink to this post)

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