wrote:
Very valid points and excellent suggestions. Most books and tutorials will teach you how to *set* black/white/gray points, but never teach you
how to *identify* them first. Nor do they teach you how to handle images where there are *no* true neutrals to begin with, e.g. a sunrise/sunset landscape scene. Dan Margulis’ book is an exception.
Yes. Dan’s the man!
With this awareness, I still have questions.
[re setting or (sometimes) searching for a neutral]
I normally work in the RGB mode. Why is LAB mode special in finding neutrals?
The main reason is you can set the neutral with no effect on the image’s overall brightness. In Photoshop this may be done manually to zero-ing out the a and b values for a particular color,and in Curvemeister you can just drag the neutral point around.
[re images with mixed lighting]
You may be correct that only ~5% of the images have two or more (direct?) light sources. But in addition to being lit by these couple of (direct?) light sources, an object in an image is also lit by indirect and reflected light sources. It is not always necessary to
correct the
multiple light sources. When it is, I find applying curve based on these objects can mess up the whole image, and masking these objects is one way out.
Absolutely. I almost never mask – but there are occasional images where it is necessary.
IMHO, a gray card or other calibrated card in the scene is usually not helpful, and can be very misleading in mixed lighting situations. Calibrated targets can be invaluable for
experimentation, or in a studio setting where lighting consistency is crucial. Examples would be quantitative scientific work, professional portraiture, or catalog work where a large number of images need to match one another.
I agree that a gray card is not appropriate when there are more light sources than you can account for.
Inserting an object into your images is really not practical except for posed pictures, or in a studio setting. If I were doing a set of wedding pictures, say, I might do a few frames of Macbeth checker just for insurance. In the days of film, this was a good way to tell if your film had been developed and printed correctily, and if not why not. For experimenting in Photoshop a piece of newspaper, the back of a shirt cardboard, or a page from a magazine will do in a pinch.
Standardized gray cards are another matter. Those puppies are not cheap. There are some pretty severe requiremenst for reflective standards, including stability and spectral distribution, which is non-trivial for pigment based colors. A Macbeth card is about $90, and a gray card is probably in the neighborhood of $30 to $50.
—
Mike Russell
www.curvemeister.com
www.geigy.2y.net