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Alternative Imaging Methods
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Old February 3rd, 2006, 10:51 AM   #1
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Join Date: Jan 2005
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Free software for systematic screen testing

I am on my way to posting a few website pages on systematic testing of screen materials (GG, microwax, thin-film polymer, etc).

The idea is to have a somewhat more objective method for estimating the diverse qualities of the screens.

So far I have come up with methods for easily testing the following:

-Grain Size (simple microscopy)
-Diffusion angles; very important for bokeh and hot spot (Laser pointer + angle chart that I made)
-Light loss (software plus photographic based metering)

If there are other factors to consider let me know.


In the mean time, here is a sample of Light loss testing:

-Bag material #1: ~93% transmission
-Bag material #2: ~95.5% transmission
-Thicker Pouch material: ~94.5% transmission
-Simple magnifier lens for comparison (cheap loupe): ~97% transmission

The way the transmission was computed is the following:

Display a 180RGB gray image on the monitor display (or use a light table). Stick the screen to the display. Take a picture without flash and with appropriate exposure settings so that the image is not blown out. Use my software (dowload below) to determine the average brightness ratio.


Here you can see an image of the thicker pouch material stuck to the monitor. I took a picture with the digital camera, which is acting as a very expensive light meter :)

I load the image, crop it, and copy it to the clipboard. Then I paste the image into my analysis software. The dark green square is dragged into a uniform area where the screen is. The light green square is dragged into an uncovered area but at the same horizontal level and as close as possible to the dark square.

Instantly the software gives you a reading of the average brightness values of each area (0-255) and the transmission ratio. In this case the software indicates a 95%. The measurement varies slightly if we move the squares, depending on the lighting conditions affecting the picture. If care is taken when taking the picture, the error is minimized.


You may obtain my software at:

Now we have a more objective (not perfect) method for determining the light loss of several screen materials, and even lenses!

I hope you find it useful.

Later on I will post the diffusion angle chart in pdf format so that you can download it also and make measurements for determining the diffusion angle of your screens and whether they are symmetric or not (important for nice bokeh).

Last edited by Alain Bellon; February 3rd, 2006 at 12:23 PM.
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