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COLOR BALANCING DIGITAL IMAGES WITH A GREY CARD

These helpful hints are posted here with the intention of offering information about one easy way to use a grey card (Kodak gray card or any other brand) to get better color results from your digital images.  

I'll start with a question:  If you were in Los Angeles and you wanted to drive to New York how many different routes could you take and still wind up in New York?  Lots of routes, right?  Ok, well there are countless ways to get pleasing color and color balance digital images.  This page describes one method using Photoshop that is pretty straight forward and works well.  

The bottom line in color balance is this:  You need some reference in your image that is a known neutral color.  The gray card is an easy way to do that.  

THE INTRO:  

This will be very basic stuff to some visitors to this site but it does not hurt to start from the beginning.  I am going to use some terminology here that is mine, not scientific, with the intention of putting it all into terms I can understand.  If I can understand it, anybody can!

"Real Color", as we humans see it, is the light that is reflected from an object.  There is a source of light: such as the sun, the moon, artificial lighting, a camera flash, etc.  This light strikes an object and it is reflected back to our eyes, which record it and pass it on to the brain, which interprets it for us.    An apple looks red, or green, or yellow, because the chemicals in the skin of the apple reflect back these wavelengths.  

But the "real color" of an object changes as the subtle color tone of the light that shines upon it changes.  

For example:  We see a piece of white paper in an office that is illuminated with florescent lighting.  The paper looks white to us.  We take the paper outside into the bright sun, it still looks white.  We take the paper home with us and look at it under the tungsten lights that illuminate our house; it's white.  We take it into the shade and it still looks white to us.

But it's not really pure white in each of these situations.  Our brain knows that this paper should be white so it does some fancy interpolating for us.  In reality, the paper in the office probably had a bluish hue to it, as it did in the shade too, and  it had a reddish hue in our home, and was maybe slightly yellow in the sun.

Cameras do not have the wonderful flexibility of the human brain.  Although there is some great technology out there to make these machines produce the color that we SHOULD be seeing, by correcting the WHITE BALANCE of an image as the image is captured or processed, most of them are 100% perfect all of the time.  There will be times when an image has a COLOR CAST to it, maybe a slight magenta, a bit too red, or perhaps yellow.

There are certain colors that are very important to humans, we have been looking at them for thousands of years, and we can tell when they are "not right."  Skin color is one example.  When it's wrong we know it; we have been looking at other people our entire life and we know when it's wrong!  Green grass and trees are another thing that seem to be imbedded in our brains.  When green trees are yellow or red we just instinctively know something is wrong. 

The goal of color balancing is to make the colors "right."  We want white to actually look white and for grey to look grey.  There are exceptions to this, such as those times when we want the golden light of a setting sun to look golden, but let's put that aside for now.  For the most part, if we can get an image to display white as white, and grey as grey, then in all likelihood the skin tones of the people in the photo will be corrected and look normal and pleasing to us as well. 

COLOR AND THE COMPUTER WORLD

When computers render color, so that we can see color on a monitor or print it out on paper, they need to do so in a mathematical format.  There are all sorts of complexities that enter into the display or printing of color but the standard that home computers rely upon most is going to be RGB color.  With this system there are three primary colors, RED  GREEN  BLUE.  Colors displayed on a monitor or (in the case of most ink jet printers) are a composite of these three, with each color have a value of RED, GREEN,  BLUE between 1 and 255.  Pure Black is 0-0-0.  Pure white would be 255-255-255.  Every other color, all 16,581,375 of them, are a composite of the three primary colors.  Here are some examples

       
R201 G198 B54 R168 G47 B208 R12 G250 B12 R226 G29 B88

Whenever there is an equal mixture of RED, GREEN, and BLUE we get GREY ( also called NEUTRAL) TONES

Here are a few examples

       
R15 G15 B15 R129 G 129 B129 R178 G178 B178 R220 G220 G220

DIGITAL PHOTO COLOR CORRECTION

When we take a digital image, the camera makes it's best guess regarding the "Color Temperature" of the light source and the camera firmware adjusts the color accordingly.  Sometimes the result can be very good, other times it is way off.  It depends on the camera, the way you have it set, the degree to which the light is made up of mixed light sources, and a lot of other things.  Fortunately we have wonderful software that can fix these problems for us and give us a great range of creative options as well.

Getting the proper color balance of an image is probably the most basic step in image editing.  But there can be tremendous confusion among digital camera users about how to get a good result.  Some software, such as Adobe Photoshop, appears absolutely alien to beginners.   It takes a long time, some dedicated study, and lots of experience to really master Photoshop.  But the most essential tasks, color balancing and tone control, are really pretty easy in Photoshop and most other image editing programs.

ENTER THE GREY CARD

One way to "make a photo look right", is to put something in it that has a known value.  The software can then correct the color of this one item, "pulling" everything else in the photo along with it, and making a very nice overall improvement.  Let's say we have a photo that has a "Reddish Cast" to it, in other words the entire photo looks just a bit too red.  I once had a camera that had a terrible problem with reddish castes, so I happen to know about this one!  

   

Here is pure gray: 

 

R200 G200 B200

Here is gray with a reddish cast: 

 

R210 G200 B200

To fix our problem we can put (or find)  something in the image that is neutral.  In other words, if we put (or find) an object in the photo that we know to be neural ( any color in which RED VALUE = GREEN VALUE = BLUE VALUE) and then let the software make sure that that object really is neutral, it will work wonders for bringing the entire photo towards more realistic color.

You can gray balance a photo by selecting any object in the photo that "looks" to be white, pure grey, or otherwise neutral, but this is not very accurate.  If it is not really neutral in color, and has a slight color caste of it's own that is not easily detectable, then we are not helping matters.    BUT... a white styro cup, or a piece of one, works pretty well.  You don't need to buy an official "grey card"

SO, this is STEP # 1, you take a photo with the grey card visible in the shot.  It does not need to dominate the shot, it just needs to be visible, and to be bathed in the same light that you are shooting in.

Obviously, It is not practical to physically place a grey or white object in each and every one of our shots.  Don't worry; that's not where we are headed.  But we can take the results of the photo with the gray card and extend the settings to other photos.  Read on.....

 

IMPORTANT SIDE NOTE:  As Mark Twain once said "There are lots of ways to kill a cat"; and the same holds true for white balancing a photo.  There are lots of totally legitimate ways to do it and the end result will be pretty much the same.

Here are a few ways:

1.  Many cameras offer in-camera software to utilize a gray card to set a "Custom White Balance."  You take one shot with a gray card and then use that shot as a reference for the following shots you will take in that light.  The documentation for your camera will be the best guide in telling you how to use the shot in these situations. 

2.  If you are converting an image file from some RAW format (via BREEZEBROWSER, CANON RAW IMAGE CONVERTER, CAPTURE ONE, ETC) to either JPG or TIF, you have many options for setting the white balance DURING THE FILE CONVERSION, using the image that includes the gray card as a kind of template.  Basically, you white balance the gray card shot and then extend that same white balance to other selected images taken under the same light conditions.  This is actually the best way to do it, in my opinion, and the way that I do it myself..  The documentation for your conversion software will be the best guide in telling you how to use the shot in these situations.  

3. BUT MY PURPOSE HERE... is to describe another way, a very easy way  to color correct images in Photoshop and then to build a library of WHITE BALANCE settings that you can use over and over again..  For practice purposes here, you should bring your gray card shot into PHOTOSHOP AS YOU SHOT IT,  with no pre-adjustments or white balancing by other software.  There is nothing wrong with TWEAKING an image that came out of another program already white balanced, but for this exercise, you would not be able to use the results to build a library of Custom White Balance Settings.

4.  Within Photoshop there is one more choice to be made: there are two ways to white balance a photo.  We can use LEVELS or CURVES.  CURVES is more accurate, but it takes more skill to use CURVES, so we will use the LEVELS function. 

NOW IT'S PRACTICE (AND REVIEW) TIME 

 

Go out and take a photo with your gray card.  Some things to keep in mind:

 

It does not need to occupy a major portion of the frame.  It just needs to be plainly visible.

 

Anything white, grey, or both will work.  But remember that you want the object to be really grey or white, and not have any color cast to it.  They grey card is also handy because they are small, fit in a bag, and you don't need to go looking through the nearest dumpster for something white or grey when you need it; you have a little card that meets that need.

 

If you are taking portraits you can have someone hold the card, with both the card and their face visible.  This will help you to see if the gray card helps to get the skin tone right.

 

Make sure the card is illuminated with the light you will be shooting in.  If you will be shooting with a flash indoors at night, then take your gray card shot indoors at night using the flash.  If you are outside on a cloudy day, take your shot under those conditions, and so on.

 

The light should strike the card uniformly and you should take the shot more or less straight on.  The card should not be tilted at too much of an angle.

 

Make sure the shot is properly exposed.  

 
 

Here is my test gray card shot.  

It was taken under florescent lights.  

At first glance it might look OK, but there is a bluish caste to the image.  Overall impression is that it does not have enough contrast.

LET'S FIX IT!

 
 

1. OPEN PHOTOSHOP

 

 

2. OPEN YOUR GRAY CARD IMAGE

It can be in any format:  JPG, TIF, etc

 

3. click IMAGE> ADJUSTMENT> LEVELS.

 

 

 

4. Click on the middle eye dropper, the one that says "SET GRAY POINT"

 

5. Position the eye dropper over the gray card and click

 

You should see an instant improvement in color.

 

What has happened here is that you told the software that the item you clicked on was gray.  The software found that it actually had a bit too much blue in it so it corrected that, making the card gray again, and removing some blue caste from the rest of the photo as well..

 

 

A CUSTOM WHITE BALANCE LIBRARY

This is the real gem!

Before you move on, you can save this "white balance adjustment" so you can use it again with other shots in similar lighting conditions, without having to use the card in each and every shot.

Here's how to do that:

After setting the gray point, do not make any other adjustments!  Leave the LEVELS dialogue box open and then click on SAVE.   Give your custom white balance a NAME,  and be sure to save it in a place you will remember.  

I called this one" Night Florescent"  It will be saved as an .alv or "Levels" file

 

 

 

FINAL IMAGE

After a few extra tweaks that are explained below

READ ON....

 

USING YOUR CUSTOM WHITE BALANCE LIBRARY

When you open a new image that was shot in the same light conditions as your gray card shot,  click on IMAGE>ADJUSTMENT>LEVELS, and then "LOAD".  

Navigate to the folder where you saved your Custom White Balance file ( the Levels .alv file) , click on the file, then ZAM BAM......your image is white balanced!

 

HERE IS AN IMAGE THAT WAS SHOT UNDER SIMILAR CONDITIONS TO THE VASE SHOT BEFORE LOADING THE SAVED CUSTOM WHITE BALANCE (.alv) FILE.

 

 

HERE IS THE IMAGE AFTER LOADING THE SAVED CUSTOM WHITE BALANCE FILE

 

YOU CAN SAVE WHITE BALANCE FILES AND USE THEM OVER AND OVER AGAIN

Since no two light conditions will be exactly the same, and if you are a perfectionist, the best results will come from taking gray card shots at the beginning of each shooting session, for each light condition.  But you can get great "nobody-can-tell-the-difference" results by loading the LEVELS files you have previously saved.  

 
FINAL TOUCHES

This image above is still too dark.  So to finish things off, and still using LEVELS, we will adjust the highlights, the shadows, and the midtones.

With LEVELS open, slide each of the small triangles below the "histogram" scale inward until they meet the beginning of the graph.  In this image the dark SHADOWS end of the scale (left side) needs no adjustment, but we can slide the right side (HIGHLIGHTS) in a little bit to the left.  That will brighten things up some.  When that is done we adjust the MIDTONES by sliding the center triangle back and forth to either make things brighter or darken them.  In this case we need to brighten the MIDTONES so we move the slider to the left.

 
A FINISHED IMAGE!

It is still far from perfect, but this is not intended to be world class photography, just a quick and easy lesson!

 
OTHER WAYS TO KILL A CAT:

You will notice that there are little eyedroppers to the right and left of the SET GRAY POINT dropper.  The one on the left is SET BLACK POINT and the one on the right is SET WHITE POINT.  You can use these instead of sliding the little triangles along the scale.  Click on the SET BLACK POINT eyedropper and then look at your image very carefully to find the absolutely darkest spot, preferable full black.  Click on that point.  Now click on the SET WHITE POINT eyedropper and and find the absolutely whitest spot (but not an overexposed "blow out") and touch that spot.  You have just done essentially the same thing as using the sliders.

STILL ANOTHER WAY

You can use CURVES instead of levels, the eyedroppers work the same way, but a full lesson on CURVES would fill much more than this page. :   

STILL ANOTHER WAY

If you are converting your images from some RAW format to JPG you will have the greatest flexibility to set the correct white balance.  But remember that the "correct white balance" might be different from the absolute white balance.  By this I mean that there are times when you will want your images to have a golden glow to them, or when you will want the bluish hues of snow or deep shade.  "Correct Color" is in the eye of the photographer and there is lots of room to be creative with that

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