Adobe Photoshop correction of fluorescent lights on daylight film

Discussion in 'Medium Format' started by thomas_diekwisch|1, Dec 1, 2002.

  1. This is not really only pertaining to MF but also others, but I am
    posting the question here since the level of responses is so high.
    O.k. I am taking pictures of interiors lit with fluorescent lights
    on Fujichrome Provia. I am scanning the slides using an Imacon
    Flextight Photo and I am processing the images using Photoshop. For
    some reason I don't get the color balance right. I know it needs to
    go toward "purple" and away from "green", but that's about it. Any
    suggestions/help?
     
  2. Towards magenta is correct but some fluorescents have peculiar "spiky" colour output and if two or three different versions are mixing .... Also if you have other light mixed in (daylight or other artificial sources) the combinations of spectra are endless. Suggest you get as acceptable as possible with "colour balance" and then go into hue/saturation control and investigate all the options there (saving versions as you go). Very likely you will have to settle for acceptable rather than perfect . Location video crews often carry magenta filter sleeves to slip over tubes when working in mixed light - I think their lighting overpowers everything but when a tube actually appears in shot the filter corrects it to white. Might be a technique to ry though if you do a lot of this. What's the betting that in five minutes time someone comes on explaining that P/shop has a plug in just for this eventuality?
     
  3. If you aren't using one, the first thing to try is an FLD filter.
     
  4. You want it to go towards magenta and slightly towards red, butthe problem is
    beter solved using an FLD, a CC30m or cc40M or whatever combination of
    cc (color correction) filters is recommended by Fuji for the particular type of
    fluorescent tubes being used i nthe room(s) you are photographing. This is
    one of those things that is better solved in camera than in post processing.
    <P>Another Photoshop processing approach might be to make two duplicate
    layers of your background layer. You will use these as "Curve Adjustment"
    layers, and you should try this in the conbined RGB curve, not the individual
    R,G or B channels. In the first layer, find something that you know is absolute
    white (the value of that spot should be in the 248 or higher range) and select
    the white point eyedropper tool to shift the curve so that point is now 255. this
    will shift the entire color curve. Now go to the second duplicate layer and find
    a point that is black or near black (the existing values for the "black point'
    when you are searching should be between 0 and 7). Now select that point
    using the black point eyedropper toolon the curves adjustment palette. In the
    layers palette menu of Adobe Photoshop 7.0, you can selectively adjust the
    opacity and fill levels of either adjustment level to make the best color match.
    To get the best results this approach requires you to be working on an
    accurately calibrated and profiled monitor.
     
  5. Try setting the white point on or very near one of the lights. This should clean up the color cast.Do it in curves and when you get an adjustment that looks good save that curve so you can apply it to other scenes with the same lighting. Applying the same correction will help all your work match. If the scene does not contain any daylight or other different light sources you really should use a FLD filter to correct for the fluorescent lighting. You might still need to do some fine correctioin in Photoshop but not nearly so much.
     
  6. The real problem is that fluorescents do not emit the full spectrum of light, unlike tungsten, daylight, or flash. So even with correction filters, color saturation will be less-than-perfect; and since there is quite a lot of variation between types of fluorescents, no one correction (over the lens or in PS) will be the answer every time. Multiply by the possibilities of mixed lighting and it's a custom correction every time.
     
  7. Remember to use exposures of 1/60 or more to average out color and brightness variations of fluorescent light during an AC cycle. Shorter that 1/60 exposures may cause inconsistent color cast from frame to frame even in the same setting. regards
     
  8. cg

    cg

    This might be a late response but they might be useful for future work. Do you really have to shoot transparency? I've shot Provia III with an FLD filter under unknown flourescent lighting and the results were very green. The FLD filter is too weak. I ended up correcting the scans in Photoshop using curves. Using an FLD filter will not do much. Here are the CC filters you'll need for PROVIA 100F (RDPIII):

    Flourescent Type:
    Daylight(D)= 30R+10M
    Cool White(CW) = 35M
    White(W) = 25M+20B
    Warm White(WW) = 80B+15M+10R

    These are from the Fuji Data Guide. They are guidelines only and you will need to run a film test or use a colour meter because flourescent tubes are not colour consistent throughout their lifespan.

    Is it a mix lighting situation or all flourescent? If it is mixed you may have to individually wrap the flourescent tubes with the approriate filters. You can get large sheets of filters from Lee or Roscoe. BUT You can consider using Fuji negative film with the 4th layer technology such as NPS, NPC or NPL. They are specially designed for mix lighting. They scan well in the Imacon but they are grainier and will also require a bit of cleaning up in PS. Good Luck
     
  9. Thomas,

    Download a trial copy of Photoshop Elements from Adobe. Its free for thirty days. There's a tool called color correction and you use it to pick white or neutral gray points in the image. The program does the rest. Our experience with it has been uncanny. Since Elements is marketed to the consumer market Adobe has seen fit to develop a plug-in to correct photo color cast problems. We make the color corrections in Elements and then do the rest of our work in Photoshop 7.

    Good Luck
     
  10. You could always try using "Auto Tone Correction" in PS and then adjust manually from there. Or use "Variations" and increase the magenta tone little by little.
     

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