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Photoshop Help Please

Discussion in 'Retouching and Post Processing' started by sbutchin, Mar 24, 2007.

  1. sbutchin


    Mar 1, 2005
    Can someone explain the process of how to take a photo into photoshop and examine it to determine how many stops it is + or -
    i know my stuff is always off, so it would be great to be able to examine it in photoshop and see where my problem lies
    thanks so much as always
  2. Stephanie
    Are you shooting RAW images? What photoshop software are you using?
  3. Your best bet is to start with Levels..... but you have to study Levels to understand what the histogram is telling you. Then you'll be able to apply the theories to your images.

    Anyone have a link to an excellent Levels tutorial?
  4. sbutchin


    Mar 1, 2005
    jpeg, cs2 although it says version 8.0 when it boots
  5. Lowolf


    Jan 26, 2006
    If saying version 8 means you have Photoshop cs installed agree work with levels from the palette well and hold down the alt key (option key if a Mac) when making adjustments with levels
  6. sbutchin


    Mar 1, 2005
    but how do i tell how many stops i am off by? any tutorials out there? thanks again
  7. Iliah


    Jan 29, 2005
    Dear Stephanie,

    Underexposure and overexposure are subjective terms. Objectively, you can only evaluate how well the dynamic range was used in the shot.

    There is no way to determine exactly in Photoshop by how much the image is above dynamic range (that's my way to say "overexposed"), because the information is clipped, and we do not know how much of it is clipped.

    For shots that under-employ dynamic range ("underexposed"), look at the white point slider in the green channel of Levels dialogue. White point at 250 is 1/3 eV under, and so on, green channel white point is the left column, exposure adjustment to use the dynamic range of the camera to its full extent is the right column:

    250 = 1/3 eV
    242 = 2/3 eV
    218 = 1 eV
    196 = 1 1/3 eV
    177 = 1 2/3 eV
    159 = 2 eV
    143 = 2 1/3 eV
    129 = 2 2/3 eV
    116 = 3 eV (this is famous 18% grey, 17.78% to be exact)
    105 = 3 1/3 eV
    94 = 3 2/3 eV
    85 = 4 eV
    77 = 4 1/3 eV
    69 = 4 2/3 eV
    62 = 5 eV
    56 = 5 1/3 eV
    50 = 5 2/3 eV
    45 = 6 eV
    41 = 6 1/3 eV
    37 = 6 2/3 eV
    33 = 7 eV

    You can use a transparent tape with markings on the camera LCD to take away guesswork.
  8. Open the image in Adobe Bridge, Nikon Capture 4.4, Apple Aperture.

    I don't think PS CS will let you know stop values.

  9. Iliah


    Jan 29, 2005
    > Open the image in Adobe Bridge, Nikon Capture 4.4, Apple Aperture.

    Dear Greg,

    I have not checked Aperture, but ACR and other Adobe products report eV inaccurately.
  10. If your camera allows a Histogram review, once you understand Levels and what it means, you'll be able to read your Histogram out in the field to know if your exposure is correct. Basically, if everything is hunched way over to the left, you're underexposed.... if everything is bunched way over to the right, you're overexposed. This is VERY generic wording just to get you started.
    Post up a couple of picture direct from your camera, with no processing in Photoshop and we can start you from there. We'll show you what the levels/histogram of the shot is and where it should be if it's off....
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