How do I find neutral gray point – help?

Lynn wrote:

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

Look for a color in your photo that looks as close to gray as you can find. Click the midpoint eyedropper on that color. I recommend using Curves instead of Levels for most operations due to the fact that you can uniquely control all 255 shades of gray. If you don’t have ANY gray in your photo, do a test shot using a calibrated Gray Card Wedge Step (A card calibrated with pure gray color on it). Use that card in your test photo, remove the card for your actual photos, you can calibrate color and remove color cast from the first.

—

__________________________________________________
Leo McKenzie
www.solocomputerservices.com/scsgrafx.php

do a test shot using a calibrated Gray Card Wedge

Where does one find a calibrated Gray Card Wedge

In article ,
(Joyp) wrote:

do a test shot using a calibrated Gray Card Wedge

Where does one find a calibrated Gray Card Wedge

Take your pick

http://www.calumetphoto.com/ctl?PAGE=Controller&ac.ui.pn =cat.CatItemDetail&ac.item.itemNo=IM6810

http://www.calumetphoto.com/ctl?PAGE=Controller&ac.ui.pn =cat.CatItemDetail&ac.item.itemNo=KB1804

I’d like to chime in once more with a different tack on selecting a neutral gray point in an image. After selecting a highlight and shadow, getting rid of any overall color cast is the most important color correction operation.

The term "neutral gray point" is normally used in color correction, and in Photoshop selecting a gray point can be done by placing an eyedropper point on an object in the image that is known to be gray. Then use curves to make the red, green, and blue values equal.

It’s very important that the object be one that is truly gray, and not something that is suspected gray. For example, an article of clothing may be ivory or light blue. As someone else mentioned, the lower edges of clouds are normally a perfect gray color. Sidewalks, asphalt streets, kitchen appliances, sheets of newsprint, brushed aluminum or steel, iron, a bar of ivory soap, etc. The list goes on, and it is based on our common knowledge of the world, or our memory of the scene.

I have to confess to sometimes picking a variety of "gray" objects, and setting on an object that, when neutralized, makes the rest of the image look good. This is particularly easy to do using the Curvemeister plugin in Lab mode, which allows you to drag the neutral around and see how the colors change. The gray eyedropper in Photoshop curves behaves in a similar way, but is disabled in Lab mode, which is my favorite color space for finding neutrals.

Some images – roughly speaking one in 20 – have two light sources. An example would be a person standing near a sunlit window. The interor lighting is normally colored by the objects and walls of the room, or artificial lighting, and will create a different color cast than the light from the window. These are difficult images to deal with, and in extreme cases may require that a mask be used to separately color correct the different parts of the image. Luckily such images are rare.

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.

There is additional material about neutral points, plus a free demo with tutorials that include setting the neutral point, at the Curvemeister site. —

Mike Russell
www.curvemeister.com
www.geigy.2y.net

Lynn wrote:

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

A note on using the Eyedropper. I read somewhere that whatever Grid size(Single pixel, 3×3 grid avg., or 5×5 grid avg.) you select when using the Color Picker Tool, that size stays with all your color picking from that point on.
Make sure you have it set at 3×3 average or even 5×5 average, and not on Single Pixel color picking. If you want to see the variety of colors in a Grey background, zoom in to Pixel level magnification. If you average the colors in a 3 or 5 square grid, you have a better chance of hitting a grey average.
nikki

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.

With this awareness, I still have questions.

Mike Russell wrote:

I’d like to chime in once more with a different tack on selecting a neutral gray point in an image. After selecting a highlight and shadow, getting rid of any overall color cast is the most important color correction operation.
The term "neutral gray point" is normally used in color correction, and in Photoshop selecting a gray point can be done by placing an eyedropper point on an object in the image that is known to be gray. Then use curves to make the red, green, and blue values equal.

It’s very important that the object be one that is truly gray, and not something that is suspected gray. For example, an article of clothing may be ivory or light blue. As someone else mentioned, the lower edges of clouds are normally a perfect gray color. Sidewalks, asphalt streets, kitchen appliances, sheets of newsprint, brushed aluminum or steel, iron, a bar of ivory soap, etc. The list goes on, and it is based on our common knowledge of the world, or our memory of the scene.

I have to confess to sometimes picking a variety of "gray" objects, and setting on an object that, when neutralized, makes the rest of the image look good. This is particularly easy to do using the Curvemeister plugin in Lab mode, which allows you to drag the neutral around and see how the colors change. The gray eyedropper in Photoshop curves behaves in a similar way, but is disabled in Lab mode, which is my favorite color space for finding neutrals.

I normally work in the RGB mode. Why is LAB mode special in finding neutrals?

Some images – roughly speaking one in 20 – have two light sources. An example would be a person standing near a sunlit window. The interor lighting is normally colored by the objects and walls of the room, or artificial lighting, and will create a different color cast than the light from the window. These are difficult images to deal with, and in extreme cases may require that a mask be used to separately color correct the different parts of the image. Luckily such images are rare.

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.

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.

There is additional material about neutral points, plus a free demo with tutorials that include setting the neutral point, at the Curvemeister site. —

Mike Russell
www.curvemeister.com
www.geigy.2y.net

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

Mike Russell wrote:

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.
—

Setting and correcting w/b/gray points is a great way to fix an image, *provided* that these points do exist in the image *and* you know how to identifying them. All the books and tutorials will use examples that contain real w/b/gray points which are easy to identify. And they work great. But in the real world, as discussed above, in many images these points are difficult to identify or simply do not exist. Correcting this kind of images right really separates the men from the boys (or women from the girls).

Several color casts typically exists in these difficult images and there are no w/b/gray points. I want to preserve the desirable cast(s) (sunrise/sunset glow, candle light indoors, etc.), but at the same time remove the undesirable cast(s). If I apply curves to channels iteratively to remove the casts, my lying eyes and short memory cannot keep track of whether one edit is "better" than another. What I need is a way to compare the edits side by side. I find PS’ Variations to be rather crude for this purpose, and duplicating the image in multiple windows to be tedious.

wrote:

Mike Russell wrote:

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. —

Setting and correcting w/b/gray points is a great way to fix an image, *provided* that these points do exist in the image *and* you know how to identifying them. All the books and tutorials will use examples that
contain real w/b/gray points which are easy to identify. And they work great. But in the real world, as discussed above, in many images these points are difficult to identify or simply do not exist. Correcting this kind of images right really separates the men from the boys (or women
from the girls).

Several color casts typically exists in these difficult images and there
are no w/b/gray points. I want to preserve the desirable cast(s) (sunrise/sunset glow, candle light indoors, etc.), but at the same time remove the undesirable cast(s). If I apply curves to channels iteratively to remove the casts, my lying eyes and short memory cannot keep track of whether one edit is "better" than another. What I need is
a way to compare the edits side by side. I find PS’ Variations to be rather crude for this purpose, and duplicating the image in multiple windows to be tedious.

Good point. Check out the Compare button in the Curvemeister demo – it will toggle between the corrected and uncorrected images, and you can also quickly switch between color spaces and compare your work in each color space as well.
—

Mike Russell
www.curvemeister.com
www.geigy.2y.net

To the other excellent responses I’ll merely add the following:

1. Your perception of a color cast is most acute in the lighter values. Neutralizing the white point goes a long way toward getting a pleasing (as opposed to objectively neutral) color balance.

2. Don’t forget to look at shadows on known white objects. These may likely be middle gray. Keep in mind that outdoor shadows are blueish – try try going halfway toward neutral with them (using the RGB numbers in the Info palette) or equalize the R and G numbers.

3. Without a known white or gray object in the scene, the viewer will have as much difficulty as you in detecting a color shift.

4. In people photography, viewers have a wide tolerance for warm (yellow-to-red) color shifts.

Tom Nelson
Tom Nelson Photography

These are very helpful points to keep in mind when dealing with neutrals (or lack of). Just like neutrals, there are recommended color values for the different skin tones. But remember that these values are for the skin tones *without* any cast(s). They need to be corrected just like correcting neutrals, i.e. taking desirable and undesirable cast(s) into consideration. Since most viewers are more familiar with or critical about skin tones, getting them right is even more important than neutrals.

Tom Nelson wrote:

To the other excellent responses I’ll merely add the following:
1. Your perception of a color cast is most acute in the lighter values. Neutralizing the white point goes a long way toward getting a pleasing (as opposed to objectively neutral) color balance.

2. Don’t forget to look at shadows on known white objects. These may likely be middle gray. Keep in mind that outdoor shadows are blueish – try try going halfway toward neutral with them (using the RGB numbers in the Info palette) or equalize the R and G numbers.

3. Without a known white or gray object in the scene, the viewer will have as much difficulty as you in detecting a color shift.
4. In people photography, viewers have a wide tolerance for warm (yellow-to-red) color shifts.

Tom Nelson
Tom Nelson Photography