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Field De-interlace methods

There are several methods of getting rid of fields in interlaced video footage.

Here's our original test image. It was created in photoshop, and it's designed to show the artifacts created by each de-interlacing method as clearly as possible.

Let's look at it enlarged 200%

You can see the anti-aliasing created by photoshop's drawing tools clearly. The upper thin lines represent the odd and even fields of the footage. If watched in a video monitor, the above image would flicker notoriously. The fields represent motion in this test.

The first two images are the odd and even fields, de-interlaced by duplication:

(Essentially the same thing as just reducing the vertical resolution to half without resampling)

There is strong "jaggies" aliasing artifacts visible

The next ones are the same images, but with the interpolate method of photoshop:

The jaggies are still there, but a bit blurred.

Also, this method loses half of the motion information in footage, which usually is not desirable, introducing strobing.

Next let's see, what happens, when the fields are blended together 50%:

The left one is with interpolation, and the right one without it.

The left one is quite good, the in-frame motion (lines) has been blended, and there are no apparent jaggies, except in the upper diagonal area, but that's not a big problem, as it is a place where motion meets static, and therefore the aliasing will not prolly be noticeable in moving video.

Now let's check out another method, blurring the image with photoshop's motion blur 1 pixel, with 90 degree angle:

(This can be reproduced exactly in Speed Razor with 0.3 vertical fast blur. Also, the DeFlicker filter does this same thing quite nicely, and for Premiere you can use "reduce interlace flicker", in After Effects both are available)

These methods are naturally thousands of percents faster than batch applying photoshop filters to exported still sequence.

As you can see, it de-interlaces beautifully, and with sharper result than any of the above methods. The horizontal resolution is maintained perfectly, and the vertical resolution, though reduced, is reduced far less than to half (See example of half vertical resolution below)

All image scaling in these examples was done with photoshop's Bicubic resampling

If 1 pixel blur works so well, what will 2 pixel blur do?

Actually it doesn't work too good... in addition to blurring the image more, it doesn't completely remove the fields.

Look at the image below: The left side is 1 pixel blur, blending every pair of lines together. In the middle is 2 pixel blur, which spreads the blurring effect wider thus not being not as effective. The right side is the original three lines.

Blurring more than 2 pixels de-interlaces well, but results are not acceptable due to heavier blurring.


 

The next ones are 1/2 resolution image, and the half rez image Resized to original size in photoshop. As you can see, even reducing the resolution to half (Both horizontal and vertical ), with a good algorithm produces better results then Photoshop's de-interlace as is.
 

Let's look at the two best methods again at 300%, the first one being motion blur, and the second blended, interpolated de-interlace:

As you can see the MB approach's results are a little sharper.

The original looked like this:

Then again, at original size the the differences are almost unnoticeable:

This concludes this experiment - happy producing folks!

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