4

In Lightroom and other such programs, color temperature for lighting is easy with an eyedropper tool if you have a true neutral in the photo, such as a grey card. For a natural object, it gets you close enough to fiddle with, usually.

What about matching a known color that's not grey? For example, an article of clothing that can also be shot as an exemplar at another time.

There are color plaques used for photography, some quite pricy. How are they used other than by manual fiddling by eye?

Furthermore, the color temperature + tint model doesn't seem to be as effective with various indoor lighting sources, which I suppose don't have nice black-body spectra.

Is there a tool (preferably to use with Photoshop) that can do such color calebration?


Clarification: I know how to use the gray card (I prefer a cloth to get different angles at one go) in a preliminary shot (implied by mentioning the eyedrop-on-gray tool). My question is specificly how to handle not having that, and bad large-area lighting as well.

2

You can do this manually if you know what the color is supposed to be. It is similar to the process of calibrating to a neutral sample. The results will not be as accurate as if you use a grayscale, especially with mixed color lighting.

You should work from a RAW file if available.

  1. First, set a best guess white balance.
  2. Measure the known color in your image in terms of R,G, and B (Red, Green, Blue) values
  3. Compare the measurement to your target
  4. Adjust the white balance accordingly
  5. Repeat from step 2 until the color is matched

Example: if the sample is 55,87,123 and it is supposed to be 55,82,125 you will leave the red alone, take out some green, and add a little blue.

Hint (added after your followup) to make RGB edits with temp/tint:

  • To add red: Add yellow and magenta.
  • To remove red, remove yellow and magenta.
  • To change blue, use temp.
  • To change green use tint.

Caution: when sampling the color, especially a fabric use a large sample (example 20x20 pixels) instead of a point sample to get an average reading.

Be aware that there are color shifts that can occur at certain hues and values, for various reasons, that will affect some parts of the image but not others.

Another tip: If you want to save money, get some paint sample cards from a home improvement store, including neutrals, and paste them to a piece of foam board. This would be better than calibrating to a shirt.

  • I have a grey cloth and a IT-8 target I'll shoot if I can carefully set up. I mean to have a way to handle things less intrusively, using known items that I can match with. Items that are not added for that purpose, but are acfually in the photo. – JDługosz May 24 '15 at 18:36
  • Lightroom has Temperature and Hue. Are you saying you can adjust RGB sliders somewhere as well? I think simply adjusting the channels will be OK for a slight tint of colored light, but doesn't do anything with spectral curves which are generally not simply more of one channel uniformy across the board. Fixing one color that way messes up the others. – JDługosz May 24 '15 at 18:40
  • Use your IT-8 target for the first shot. Then remove it from the shot. Then complete the photo shoot. When editing, calibrate the image with the IT-8 target. Save those calibrations and apply to the other images. – A K May 24 '15 at 18:53
  • By the way, if you have color casts that are local (not over the whole image) the problem can be mixed light or bounced light. Some lights are not calibrated, and if you use more than one there will be a mix of color temperatures. Also objects in and near your scene (especially non-neutral walls) will impart color. – A K May 24 '15 at 18:59
  • Omce again, I use the cal targets in a preliminary shot when I have time in that spot/situation/environment. Do you think I'm a complete idiot? Yes, I then shoot without it and apply the correction to the whole set. That is notnwhat I'm askimg here. Suppose I have an opportunity for a photo with a famous person, and need tombet in and out without taking up time or making a fuss. No calibration shot. Only items in the photo can be used. – JDługosz May 24 '15 at 19:04
2

Ouch... You have a nightmare scenario.

I'm making some initial questions just as an excercise of posible scenarios.

1) You know the color of the samples... but Are the ilumination angles the same?

2) Is the response curve diferent between shoots?

3) Do a linear editing of the curves enought? or should I modify the gamma of each channel? How about the levels and not the curves?

4) Do I need to match just a plain sample or that sample in good light, and the shadow area aswell.

This basicly will be try and error aproach.

A basic methodology

  • Copy your initial layer. Leave the background as a reference.

  • Make some initial adjustments on this second layer. Use correct names for them like "More Red 15%"

  • You can "over-do" a little the correction. Later if you play with the opacity of the corrections you can match it better.

This oldie animated gif was intended for other tests but the idea is the same. The first image has an exagerated efect and the second one has no efect at all. Play with transparency and choose.

http://otake.com.mx/Foros/ControlVolumeLight.gif

  • Working in layers will help you adjusting large bad iluminated areas, aplying masks. You make an exagerated correction and mask with gradients for example the amount of correction aplied.

  • You also can make some layers with notes, for example a square indicating your area of interest, so you keep measuring that part of the image.

http://otake.com.mx/Foros/MaskWhatYouNeed.png

  • People take many photos at convention centers, since the age of smartphones. They are generally bad due to horrible area lighting and low light levels. I think your point is to address each item (skin tones and recognizeable colored objects) separately. I wonder if a profile exists for various kinds of common industrial lighting? – JDługosz May 25 '15 at 16:39
  • The problem then is not only the profile for the light (halogen for example) but that exact light (old, new) but how the camera reacted to that light (smartphone model, settings, usage, fingerprints on the lens) So its a nightmare or you can try some fast empiric aproach. Let me add some diagrams on the "masking" idea. – Rafael May 25 '15 at 16:46
  • If this is this is the scenario, adjusting a buch of photos from an event, I would trust in some auto correction tools, and leave open a photo I need as a reference. – Rafael May 25 '15 at 17:03
0

Is there a tool (preferably to use with Photoshop) that can do such color calibration?

Try looking at iCorrect EditLab Pro http://www.pictocolor.com/editlabpro.htm enter image description here

It has a feature to do exactly that. Here is how to add a "Memory Color" - I'm picking one of the colours from ColorChecker reference rendition to sRGB, the "purple", and after Opt/Alt-Click on a free slot (I used the one to the right from "S" - skin, it is highlighted) a dialogue appears. enter image description herePress "Set from Hue Handle", fill the Name and Label fields, optionally save the preset, and press OK. Now some other file may be opened and the saved hue edit preset applied. It is better to keep colour space consistent, that is if the custom colour is memorized from an image in sRGB, to apply it also to sRGB images.

  • 1
    That plugin doesn't seem to address the problem anyway. It has the usual neutral dropper tool and some hue controls that you can eyeball (as far as I can see). – MikeW May 24 '15 at 22:33
  • @MikeW : well, "seem" is a "seem". Try and see. It is one of the very few professional tools in colour correction. It even allows to create correctional colour profiles. – Iliah Borg May 24 '15 at 22:52
  • 1
    Thanks; that reminds me that I used an ancestor of that 15 years ago, before "color temperature" was a feature in Photoshop and Raw files did not exist yet. – JDługosz May 24 '15 at 23:55
  • @mikeW if the panel shown lets you eyedropper the scene to point to what should be the reference color, then it does address the question. I think I used it around the year 2000, when even color temp adjustment was not available in Photoshop etc. and doint that with RGB sliders was frustrating. – JDługosz May 25 '15 at 0:09
  • @JDługosz : Raw did exist, but it was sooo niche at that time. Yes, this product is around for many years, and it is based on high grade scanner software. It allows to add memory colours to the list and reproduce them very closely in one click. – Iliah Borg May 25 '15 at 0:29
0

If you have a image that you think requires colour balancing and has no obvious reference point to select, ie no white, black or grey, the you can temporarily covert the image to black and white and look or or use the White balance picker to select a netral grey area. Remember that spot and recovery to colour and select it with the picker. Grass, road surfaces, suntanned Caucasian skin all are mid tones.

  • I don't understand. How does the b&w version help with color correction? After conversion it will all be neutral. What do midtones have to do with it? – JDługosz May 27 '15 at 14:57
  • How can it all be neutral? In that case the whole image would be one tone – adwb May 27 '15 at 19:32
  • The greyscale image will have every pixel neutral: white, gray, black. Using the eyedropper (white balqnce picker) for color balancing means clicking on a (should be) colorless patch. B&W means no color. "White balance picker to select a netral [sic] grey area" every pixel is perfect neutral. Pick again same spot in original image: (1) that will make a crazy white balance since it is not neutral; (2) why pick it earlier if we are to change it again? – JDługosz May 28 '15 at 2:27

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.