finding neutral gray? Please help?

Hi, I am occasionally having colour cast problems with some of my
photos and I know I should be finding a neutral gray point on my photo
and then using the grey eyedropper in levels to help. Problem is, I
can't seem to FIND neautral gray in color images.
I can get the blackest and whitest points using threshold and am
wondering if there's a similar way of finding grey?
I'm sure many people can simply look at a photo and see where gray is,
but I, sadly, don't seem to be one of them. If there's a way in PS CS
to find the grey, I would SO love to know what it is. Thanks so much
for all ideas! Lynn

 

Setting black and white points (or shadow and highlight) is probably the
single most important correction you can make to an image. Using threshold
is actually a rather blunt instrument that can cause color casts in your
final image.

Common gray objects: sidewalks, white shirts, asphalt pavement, household
appliances.

The Curvemeister plugin has several features to help you deal with finding
the gray. When it is necessary to feel around for a gray point, I like to
click on curvemeister's Lab radio button, put down a neutral point, and drag
it around to until the image suddenly clicks in. You may do a similar move
in Photoshop using an eyedropper point, and adjusting curves until the red,
green, and blue are equal. Or set the eyedropper to HSB mode, and adjusting
curves until the Saturation goes to zero

I emphasize, though that it's best, if possible to zero in on a particular
object that you are reasonably sure is gray, and there may simply be no gray
objects in the image. In that case, you go on to the next step, which is to
avoid impossible colors in the image.

Check out the Curvemeister demo, which is 100% functional as far as the
tutorials are concerned - I have one customer who used the demo to teach a
class (!). Each of the examples deals with finding the highlight, shadow,
and neutral, and the concepts are valuable whether or not you decide to
spend the $34.95 for the actual plugin.

 

(Lynn) wrote in

Finding it in the photo takes a little bit of practice. You have to
detach yourself from seeing it as a representation of "real life", and see
it as a painting where you need to produce and apply all the colors.

Very often, if there is anything white in the scene going into
shadow, you can peg neutral grey easily. Slightly harder is something black
with bright highlights. Both of these can be pulled off of someone's
clothing without too much difficulty. You can also find something silver or
chrome - very often, in the range of reflections it displays, you'll find
grey, though it may be a very narrow band. The undersides of puffy clouds
will work, asphalt in some cases, roofing tiles, and even reflections from
rippled water.

Not knowing what kind of photography you do makes it harder to give
anything more specific ;-)

Want practice? Set your primary fill color in the color picker to
mid-grey by setting Lab color to 50-0-0 or RGB to 119-119-119, then
Select/Color Range and use a smaller fuzziness factor, 50-60 should do.
This will select all the neutral grey in a corrected image. Do this with a
few different 'typical' images and you'll soon learn what to watch for.

Hope this helps. Good luck!


- Al.

 

You can use the info tab to measure the RGB levels. Any neutral gray should
have equal values for all three colors. A bit of exploring may point you in
the right direction by showing you consistent imbalances in favor of one or
two colors.

Depending on the PS version you can try "Auto Levels" and/or "Auto Color".

That being said it is nearly impossible to judge a neutral gray by eye
without a reference, since the brain tends to "auto white balance" depending
on overall color temperature and proximity of other colors.

There is no way to find a gray point as you find a black or white point. The
latter two are based on the assumption that at max transparency a film is
going to be neutral at 255/255/255 and at max density it will be neutral at
0/0/0 (more or less). This is not necessarily true but it is usually
somewhat close.

I find that the easiest way to remove color casts quickly (color correction
is really an complicated art) is to use the color balance control. This
gives you the option of correcting colors at three different luminance
levels. If you find that a particular correction works well for a certain
type of film or situation you can save the correction as an action and apply
it easily to other images. Or you can just fire randomly with the gray point
eyedropper and hope to find something that looks good.

Needless to say, a correctly calibrated monitor is important when doing
color corrections.

My 2 cents.

Toby

 

Another way of learning to 'see' a color cast, is to use 'Image - Adjust
- Variations'. Not to actually correct a color cast perhaps, but just to
see how different corrections would change the image.

 

An easy way to find the areas close to neutral gray is to use the eyedropper
tool with the info palette active. Neutral gray (50% gray) gives an RGB
value of 128-128-128, so any value you find close to this would be close to
neutral gray. In practice, bring up levels and select the neutral
eyedropper. With the info palette active explore the image watching the
info palette. Any value where the RGB values are close to equal would be a
candidate for your selection. The value that shows the highest number would
indicate the color cast you will remove from the image. For example, if the
RGB values are 55,51,51 and you click on that spot you will remove a bit of
red from the image. The neutral eyedropper does not realign the colors to
50% gray, but only changes the image to make the values equal for the area
you select.

 

Good point. I sometimes drop an image into variations when I *know*
there's a colour cast, but can't work out what it is.

Play around with the variations a bit until you find what the problem
is, then cancel and correct the colour properly.

 

There are some good Replies to your article, but if this is happening very
often, you might want to include an 18% gray card in one exposure for
reference. That way, you will have a true reference for your capture device,
your lighting, etc. If you find the cast occurs often, you can correct it and
Save the correction to Curves, or whatever is your favourite method of colour
correction in PS. That should give you a starting point when doing the
correction.