LCD Testing Methods

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Introduction:

Things here have been changing at a rapid pace at BCCHardware and we've grown from a handful of reviews a year to have a steady stream of products crossing our bench.  Although things are changing and progressing, one thing will not change - our commitment to you the reader.  We have published several articles over the past year that have left some readers wanting more; more information, more data, more objective testing.  We have listened and have recently revamped our test bench here at BCCHardware to give you more of what you want - hard data.

We have recently purchased a luminance meter to measure lighting uniformity as well as contrast ratio on LCDs.  Also in the bag is a colorimeter that will be used for testing RGB color levels and accuracy on displays and projectors.  We've also added the very slick DisplayMate Multimedia Edition software to our bag, and will be using it to test many aspects of displays including pixel performance, response and color uniformity across the panel.

DisplayMate

 

We thought it would be best if we showed you what tools are now at are disposal and will be used for testing displays.

 

Luminance Meter & Testing:

Light Meter One of the tools that is fairly basic, but that we are perhaps most excited about is the Luminance Meter.  The DT-1308 meter is used to measure luminance on many different areas of the screen.  A widescreen display is split up into 77 areas (11x7) and measurements will be taken at 50% Brightness and 50% Contrast when testing for lighting uniformity.  In certain cases we will also measure at 100% brightness and contrast, but uniformity data will be collected at 50% levels.  

The luminance meter is also used to measure true contrast ratios.  To measure contrast ratio, we set traditionally set the contrast and brightness to 50% and measure the brightness level on a white screen.  We record that value and then measure luminance on a black screen.  Simply divide the two and you've got actual contrast ratio.

 Black Spot
White Spot
Contrast Ratio
 1.2  572.4  477:1


When using the Luminance meter, we use a darkened room and use a foam cup around the end of the sensor that blocks out any ambient light cause by other portions of the screen.  This has proven to provide consistent results time and time again.  In the chart below, the brightest point is considered to be 100% and the blackest point is our reference 0%.  The other values are obtained by calculating the difference between the two.

Lighting Uniformity - Profile
Lighting Uniformity - Profile
 Lighting Uniformity
Lighting Uniformity

 


Colorimeter & Testing:

Spyder Box Lighting uniformity is very important, but color accuracy is perhaps a little more important.  To detect and adjust color balance, gamut and saturation we have employed the use of the DataColor Spyder3 Elite colorimeter.  This unit is used to gain accurate RGB readings as well as luminance on both white and black (backlight bleeding) images.  It will measure ambient lighting to help make a more accurate analysis if desired.  The beauty of this little wonder is that it can also be used with CRTs and projectors as well as LCDs.  This makes for a very versatile product.  We have just received the Spyder 3 Elite and will use it to replace our older Spyder2 Pro Colorimeter.  If you want to see what the difference is between the two in terms of performance and specifications head on over here to see why we upgraded .
 

We are still hashing out the details of how to chart the data obtained from the colorimeter, but the bare results do provide you with a comparison of how accurate color reproduction is on the tested display.

Color Meter
Color Meter

 

The graphs below show target values, uncalibrated values, correction curves, and more using the DataColor Spyder 3 Elite.

  Target
Target Curves

 

The image above shows the ideal color curve on a display and while it may not mean much to you yet, we will be working with this data and comparing it to more displays for reference of color accuracy and calibration.  Now that we know what it is supposed to be, let's take a look at the Samsung 305T and see how close this $1500 display is to "perfect".

 

Uncalibrated Measured Curve
Uncalibrated Measured Curve

 

Ideally, we want all the colors to follow the initial curve shown above.  Although the 305T comes pretty close, we see the color values fall just under their target in the image directly above.

 

  All Curves
All Curves

 

The image above shows the correction that will need to take place in order to bring the color balance and gamma up to the proper values.  For reference, we've left all other options checked so you can see the Target, Uncalibrated, Calibrated and Correction values.

Finally, we've got our new calibrated settings.  Below is an image that shows it all together.  The bottom group of lines are the previously uncalibrated values, and the double thick line a little higher on the graph is the Target and Calibrated value.  This shows that the display is correctly calibrated and ready to go.

Calibrated
Calibrated

 

Through this calibration process, we have values that show how far the display is from "perfect".  Our goal is not simply to calibrate a display, but to see the panel variation and how much adjustment each display needs.  Not only that, some panels cannot even be calibrated to acceptable standards and the Spyder 3 Elite Colorimeter helps us test this objectively.

 

Final Thoughts:

We don't claim to be the final authority when it comes to LCD reviews.  There are other sites that have more equipment, more resources and are specialized to review LCDs.  BCCHardware simply wants to provide you with less subjective data for comparison.  We want to provide you with solid numbers to compare lighting uniforming, color accuracy, contrast ratio and more so that you can feel confident in what you decide to purchase down the road.  Don't worry, our reviews won't turn into a tech-head blithering list of numbers.  We will still test out the LCDs in the real world in terms of gaming, watching movies, web browsing and photo editing.  This new testing methodology just takes things a step further.

We believe this is progress in the right direction.  Not every LCD display or TV will be subject to the full run of tests however.  These are tools that are available, and will be used regularly, but not perhaps in every instance.  Our testing methods will no doubt evolve to meet higher standards of technology and measurement as time progresses, but for now - we welcome the additional hardware and software testing equipment listed above.

 

Article History:

  • Rev. 1.0 - Initial Release
  • Rev. 1.1 - Upgraded to Spyder 3 Elite Colorimeter

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