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White Balance Color Temperature Kelvin Meter

Important

Point the camera of your device towards a white surface, such as a piece of paper, to measure the color temperature

Measure

To measure the color temperature of light, find a surface that is white or gray. A white piece of paper works perfectly. Just make sure to avoid any colors on the surface. Point the camera towards that surface. If you direct the camera of your device towards an even surface there shall be no warning text on the screen and the app will show the measured color temperature of the light that falls on that surface. In the top left corner, the app will also recommend a white balance setting for you to use on your camera in these lighting conditions. If you want to measure the color temperature of a special light source, it is of utmost importance that you light the surface only by this light source and no surrounding light, as that would give a false measurement.

Time Between Measurements

The measurements are done continuously once every second or so, depending on what setting you use. To change the time between each measurement go to the Settings tab and click "Time Between Measurements".

A short time has the benefit that it will update the Color Temperature value, the recommended camera setting and the Automatic Warnings more often. The drawback is that it drains the battery a little quicker.

A small animated bar on the home tab is indicating the time between each measurement.

Automatic Warnings

The app tries to help you by displaying warnings on top of the camera preview screen when it suspects that the camera is not directed to an even white surface or that the light is not enough to make a reliable measurement. Note that the absence of these warnings does not guarantee that there is enough light or that the light is directed towards a proper surface. For instance, it cannot warn you if you are holding the camera towards a surface that is tinted with some color - and a tinted surface, even with a small amount of color, will typically make the measurement completely wrong. On some devices there could also be the problem that there is a warning even though the surface used is perfectly fine.

Another thing to notice is that the automatic warnings are updated according to the frequency set by the "Time Between Measurements" setting. In other words, if the chosen "Time Between Measurement" is large, you will have to wait a bit longer for the warnings to update when you move around your device.

What is Color Temperature?

Color temperature is a characteristic of visible light that measures the hue of light from a light source. Color temperatures are usually measured in Kelvin (K). Low color temperatures (below 4000 K) are called warm colors or yellowish white while high color temperatures (above 6000 K) are called cool colors or blueish white. Technically the color temperature is the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source.

Image

When is Color Temperature Important?

Color temperatures are of special interest in all kinds of color photography. The human eye easily compensates for the color temperature of different light sources. Most cameras today have a feature called Automatic White Balance, AWB, which tries to do the same. In some conditions this works fine, in other conditions the results are poor. Many photographers therefore prefer to manually set the white balance value on the camera to match the color temperature of the current scene. With this app you can measure the color temperature before doing the white balance setting on you camera, to get a more accurate setting.

You can also use this app to learn about the color temperatures in your environment. With this knowledge you can develop a better understanding of how the color temperatures vary which helps you when you are trying to master the light and colors in your photography.

Recommended Camera Setting

On the measuring screen, in the top left, there is an icon indicating the Recommended Camera Setting.

The Recommended Camera Setting is based on the measured color temperature and is a suggestion on what to use as White Balance setting for your camera.

How Accurate are the Measurements?

To measure the color temperature accurately is more complex than it might appear. On a phone or tablet, it is complicated further by the fact that all devices are different from each other. Uncalibrated values from the app can be seen as fairly good approximations. But with the use of Calibration (see below) and a proper white surface evenly lit by the light source you are measuring, you can usually get very good accuracy.

Calibration

Setting wrong calibration values can cause the measurements to become completely wrong! Please use the calibration feature with care and only if you understand what you are doing.

There are a lot of different phones and tablets. They have different cameras, and unfortunately, they also handle colors in different ways. On most devices, the app provides good accuracy without calibration, but on some devices, the measurements will deviate substantially from the true values. To compensate for this, you can calibrate the app for your specific device.

To calibrate, you need at least one light source of a known color temperature. This can, for instance, be a LED light source that is marked 3,000 Kelvin. But please note that these markings are fairly inaccurate (often a few hundred degrees Kelvin off) and they usually change during the lifespan of the LED. Still, this is often the best most have available. If possible, also use a second light source with a known but completely different color temperature to get another calibration point. Please use the same surface (preferably a white paper) during the calibration, as when measuring unknown light sources. It is also of utmost importance that you light the surface only with the light source you are calibrating with and no surrounding light.

The calibration process is as follows:

  1. Go to the tab "Calibration"
  2. Click "Set default calibration" button to reset the calibration
  3. Go to the tab "Home"
  4. Let a light source of known color temperature light a white surface, such as a white paper, without any other light shining on the same surface. Direct the camera of your device towards this surface and note the uncalibrated color temperature reading that the app gives you
  5. Go to the tab "Calibration"
  6. Click "Edit" on the calibration point called "Map from 3000 K to 3000 K" (or add a new calibration point by clicking the "Add calibration point" button)
  7. Set the "from" value to the uncalibrated color temperature reading that the app gave you in step 4
  8. Set the "to" value to the known true temperature value

Step 3 to 8 can be repeated if you have more light sources of known color temperature. Please note that the light sources should usually be more than a thousand degrees Kelvin apart to be able to improve the calibration.

Saved Measurements

You can save any measurement by clicking on the "Save" button in the top right of the tab "Home", when measuring.

On the tab "Saved Measurements" all the measurements that you have saved are shown. To add or update a comment on a saved measurement, click on the saved measurement. To delete a saved measurement, swipe the measurement to the left or right.

Magenta / Green Measurement

To complement the color temperature measurement, the app supports a basic measurement on the magenta / green axis. Negative values indicate a magenta tint while positive values indicate a green tint.

Flash Filters

The app automatically calculates what filter to put on your flash light to match the measured color temperature. You can tell the app what color temperature your flash lights have and what filters you have available and the app will tell you which of these filters to use.

Adjust the Measurement Area

The app measures the color temperature in the area indicated by the rectangle in the camera preview on the home tab. To adjust the size of that area, just drag the arrows at the edge of the rectangle, left or right. For instance, you might want to decrease the area if the white or gray surface that you are using when measuring is small or you need to keep it a bit away from your phone and hand to avoid casting a shadow over it.

Troubleshooting

If you find the measurements to be incorrect, look through these possible causes.

Are you erroneously directing the camera of your device towards the light source?

The camera shall be facing a white surface, such as a white piece of paper, and not be directed towards the light source you would like to measure.

Is the surface enlightened by more than just the light source you would like to measure?

Make sure that the white surface you are measuring on is only enlightened by the light source you want to measure and no other light sources.

Are there erroneous calibration points?

Having entered calibration values that are not correct for your device will most likely end up in giving wrong measurements. Reset the calibration (and if needed, do a new calibration).

Does the surface have a color tint?

Make sure that the surface you are using for measuring the light source is white (or gray) without any color tint. For instance a slightly yellowish paper will make the measurements be far too low.

FAQ

I reinstalled the app, how do I get Unlimited access again?

Go to the tab "Settings". Click "Go Unlimited". Click the link "Restore Purchase" in the middle of that page.

Privacy Policy and End User License Agreement

Here you find the End User License Agreement and the Privacy Policy of the app.

Contact

Feel free to contact me with questions and improvement ideas. I try to answer all emails. apps@contechity.com

app-store google play

http://kelvin-meter.contechity.com