White balance a photograph after it has been taken?

[brianstoiber]

The company I work for is going to be developing a project that involves photographing different materials. We want to capture the actual colors or as close to as possible. I was wondering, if I had a card of some type inserted in the picture of a color that I knew. After the photograph was taken, would I be able to adjust the picture so that the color in the card matched what it actually was?

We are going to be photographing in imperfect lighting conditions so this was an idea that was thrown out to maybe help with getting a better color match.

 

[SquarePeg]

Adjusting white balance after the shot is certainly possible, especially if you shoot raw files instead of jpeg. Yes you can use a grey card in the shot to make sure you’ve got the right wb but you have to know what you’re doing (correct exposure, no glare on the card, software to convert the raw file and make your adjustments).

 

[Designer]

The company I work for is going to be developing a project that involves photographing different materials. We want to capture the actual colors or as close to as possible. I was wondering, if I had a card of some type inserted in the picture of a color that I knew. After the photograph was taken, would I be able to adjust the picture so that the color in the card matched what it actually was?

We are going to be photographing in imperfect lighting conditions so this was an idea that was thrown out to maybe help with getting a better color match.

The short answer is; yes.

Given that there are some intermediate media involved, the question now is; are you trying to match the colors on your computer display or publishing them on the web, or printing them? you have to view/match the colors in the final display which might mean not matching in some of the steps getting to the final display.

I think the easiest card to match is white, although in theory any card without its own color will do.

Depending on what editing software you have, adjusting the white balance should be fairly easy.

The "imperfect lighting conditions" is raising some flags here. Don't mix lighting types and colors. If you can, use only one color of light.

 

[jowensphoto]

A card is a good idea. In addition, you can use the Kelvin white balance setting to get as close in camera as possible. Yes, RAW files (don't use JPEG, as mentioned), are flexible, but it will make editing a lot easier.

 

[480sparky]

......
We are going to be photographing in imperfect lighting conditions...... .

What do you mean by this? Dim lighting? Ambient? Mixed lighting sources? Different problems have different solutions.

 

[benhasajeep]

Just get a Grey / White card and put it in the frame before you take the picture. Set your white balance and your done (and your meetering for exposure)! Do this each time you change your location / lighting. There are several sizes available. Will not need to adjust your balance later.

Or if you really want to do it in post. Just leave the card in the frame of the shot that can be cropped away in post.

 

[benhasajeep]

https://www.amazon.com/Neewer-Balan...rds=grey+/+white+balance+card#customerReviews

Cardboard version. I have same but older Kodak version. Also have smaller versions. They have plastic folding ones as well.

 

[TCampbell]

There are two methods ...


GRAY CARDS

Most commonly you would use a photographic "gray card". A gray card is simply a piece of material which is guaranteed to be "color neutral". If you used just any "gray" or "white" object you could find (without assurances that it was "neutral") then it might have a very slight color cast and that will throw off the accuracy of the white balance.

If lighting is truly neutral, then the RGB values of the pixels in the photograph where the gray card is located will have equal levels of red, green, and blue. In other words it might read "95, 95, 95" or "112, 112, 112" ... the three numbers which indicate the amount of red, green, and blue will be the same (that creates neutral gray).

Since we KNOW the gray card is neutral gray (it was formulated to be that way), if we photograph it and the results are not equal numbers (e.g. 112, 114, 117) then this indicates that there's a color cast coming from the lighting source which is a bit stronger in the green and blue (in my example) then it is in the red. So the computer will calculate the adjustment required to bring the gray card back to true neutral gray... and once it determines this for the gray card pixel, it applies this to EVERY PIXEL in the image.


The process is this... (I shoot in RAW and, as such, the in-camera white balance setting doesn't affect the images).

1) Put the gray card in the scene along with the object you plan to photograph and the critically important bit is that it must be in the IDENTICAL lighting conditions. So if you switch locations, move lights around... it started out as a sunny day but then became a cloudy day (you were outside), etc. then all of this changes the lighting conditions.

But the graph card only needs to be in there for the one shot (as long as the lighting isn't changed)

2) Now remove the gray card, and take all the images you need.

3) Import the images to the computer and open them in whatever software you plan to use for processing (I use Adobe Lightroom).

4) View that first image ... the one that had the gray card in the scene.
5) Select the white balance tool (commonly it will have an eye-dropper icon)
6) Select a point on the gray card with the eye-dropper.

The color balance is now adjusted to the gray card.

But here's the cool bit... since you didn't change the lighting between taking that first image (with the gray card) to the subsequent images that do not have the gray card, whatever white balance adjustment was needed for the first image, can simply be copied to all the other images. Many photo-processing apps have a way to let you copy that adjustment (and if you want... only that adjustment).

This gets you back to "neutral" white balance... but it still does NOT guarantee accurate colors. It only guarantees that the colors aren't skewed based on the color temperature of the light source.

MIXED LIGHTING can be tricky. This means you've got different sources of light that are providing different color temperatures. For example, I am photographing a model standing indoors... but near a window where we are getting "white" sunlight, but the room lighting is based on incandescent (tungsten) lighting which has a yellow color cast. The light on one side of my subject is "white" and the other side is yellow/orange. If I adjust the color temperature to fix the incandescent light source (so yellow/orange now shows neutral) then the "white" side from sunlight will now appear to have a "blue" cast. This is a problem.

To fix this, you've got to match the light sources. Mixed light can happen when you use photo-strobes (which are designed to mimic "white" sunlight) with incandescent lights, sunset lighting, etc. But you can "gel" the flash by putting clear tinted "gels" on the flash that alter the color. The most common is something called a "CTO" gel (CTO stands for "color temperature orange"). Now the flash pumps ou the same color as the rest of the lighting so you have just ONE color light from all sources. Now when you take the image into the software, you can correct the white balance because you don't have conflicting colors.

COLOR CHECKER CARDS

So the next level up from using a gray card, is using a "color checker".

Unlike a gray card which just handles basic white balance, it's possible for a camera to be a bit more sensitive to certain colors than others. This can cause certain colors to be a bit too saturated or de-saturated even though the actual "color" itself is probably about right.

You can buy a color checker (e.g. companies such as X-Rite and DataColor make these things) and this is a card or board that has various color tiles on it. Each tile is a different color hue or tone. You take a photo of the scene with the color checker card present (much like you would have done with a gray card) then you put the card away and continue the shoot.

The difference is that most photo-processing software does not inherently just work with a color checker. Usually there's special software (that comes with the color checker). This software understands the specific colors on the card (even if white balance was perfect) and can recognize if the camera isn't rendering those specific colors accurately.

Suppose a camera tends to saturate the reds a bit too much. That camera will typically always saturate the reds too much. It's a property of the camera itself (although it could be the property of a filter used on the lens at the time) and not necessarily a property of the lighting conditions. This means that the color checker software can actually build a "profile" for your camera and many applications understand those profiles.

So I can build a profile for my camera that I can then add to Lightroom so that every time I import a photo taken with that camera, Lightroom will make adjustments to the color levels based on the CAMERA that I used.

The result is more accurate color.

Keep in mind that just because the camera is now producing accurate color does NOT mean your monitor (or anybody else's monitor) or your printer is producing accurate color. If you want accurate color then you need to manage color across the workflow of camera, lighting, computer monitors and printers.

You can find numerous tutorial videos (e.g. YouTube) with instructions on how to use a gray card or a color-checker.

 

[brianstoiber]

Thank you for all of your thoughts on this. You have all been extremely helpful.

 

[KmH]

Raw image files don't have a 'white balance' until the image file is converted to a visual image. Even then the white balance is not fixed and can be manipulated.
Each Raw converter application uses somewhat different algorithms and as such produce somewhat different colors when converting the same Raw image file.
A parametric Raw converter is best because the original pixels are not actually changed. Instead the 'edits' are XML line commands that alter the action of the converter algorithms.

I've long used a calibrated gray card (WhiBal Pocket Card) and a Color Checker.

You'll also need to routinely calibrate whatever display you use for editing.
Hopefully that display is an IPS (In-Plane Switching) type with sufficient color bit depth to edit effectively.
X-Rite ColorMunki Display
Most print labs recommend X-Rite products, tools and software.

Tutorials on Color Management & Printing

• Understanding Histograms, Part 1: Tones & Contrast
• Understanding Histograms, Part 2: Luminosity & Color