Video to Stills

How to get rid of "Fringing" by De-Interlacing

This is a lot trickier to understand and more complex than most people think.  But the fix is simple.

The problem is interlacing, and we will describe it in detail, along with two solutions - "de-interlacing".  If the video is desktop video (non-inter;laced) then the resulting image is fine.  But when the video is interlaced, the resulting exported image will be a single field, which only includes either just the even lines, or just the odd lines . . . missing all the visual info in between.

Camera vs Camcorder

This will be either a camera or camcorder.  Here we will speak only of digital devices, since analog equipment is so rare today.

• Camera - takes an image of one instant in time.  This does not apply to this page, since we are talking "video" here.
   
• Camcorder - takes DV (Digital Video), which is a continuous stream of pictures called "frames".  One picture, or frame - is an image of one instant in time and is truly take in one instant of time.  The problem is that the camcorder then converts this single instant in time into 2 "fields", since televisions display video using interlaced scanning, where a frame is represented by two successive fields that are painted onto the screen.  The reason they did this, was to reduce flicker - the number of frames is 30 per second, and that causes flicker.  So they break that up into two "half-frames" (fields) of odd and even lines, and display those fields at 60 per second.  This is the NTSC television interlaced scanning standard. 

Taking a Still Picture with a Camcorder

Here are several methods of shooting a still image with a camcorder:

• by recording the image to a floppy disk - in this case the camcorder acts as a camera, and does not use interlaced fields
• by recording the image to a Memory Stick or PC Card - in this case the camcorder acts as a camera, and does not use interlaced fields
• film using "progressive scan"
• shoot the film normally, capture it, and export a frame

The first two methods create clear images and they do not use the normal video processing of the camera.  The camera actually changes mode completely and becomes a regular digital camera.

Progressive vs Interlaced Scanning - this term was originally meant to describe the way that the lines are scanned onto a display - as opposed to interlaced scanning.  Using the NTSC standard of 525 lines per frame  .  .  .  interlaced scan uses two fields of 262.5 lines each, and scans all the odd lines first, and then the even lines.  Progressive scanning scans all lines in order, from 1 to 525.  This process is explained in excruciating detail on the "Television" pages. 

NOTE: the speed is usually slowed down since this takes more processing than standard 60 fields per sec filming.

The Cause of Fringing with Exported Stills from Video

In essence, the DV camcorder fakes the actual timing of the video.  It takes a snapshot of the entire image all at once and then separates the frame into two fields that are interlaced and displayed at two different instances in time !!  It would seem logical to instead film the two fields at two different times, so that as they are displayed they more closely parallel the actual timing.  But this is not how it is done, because ther NTSC standard dictates that a frame occurs 30 times per sec, and to represent a frame as an instant in time . . . the two fields must be taken at that same instant in time - not at two different instances in time..

So this method creates field pairs as it films.  Even though they are stored on tape as interlaced, sequential fields - they are taken from the same instant in time, resulting in a much clearer frame.

Therefore each "instant in time" is displayed as two instances in time, one right after the other.   That works well for moving pictures, since the flow tends to blend the successive fields together in your brain. 

How Premiere Exports Frames

As we said, video files that contain NTSC video at 30 fps - both MPEG and AVI  .  .  .  store each field as an entire image. 

Premiere 4.0 and 4.2 - exports the entire frame by combining both fields.  This seems to make more sense and gives you an image with no fringing.  However, these earlier versions of Premiere do not have the capability to export a single field, and this is necessary for some special processing.

Premiere 5.0 and later - these versions of Premiere export one field when you export a bitmap.  If the video is desktop video (non-inter;laced) then the resulting image is fine.  But when the video is NTSC interlaced video, the resulting image only includes either just the even lines, or just the odd lines . . . missing all the visual info in between.

YOU CANNOT USE Premiere Exported Images for High Quality Pics !!!  If you export a still from Premiere and plan to print it, you should know that standard-resolution video always translates to 72 dpi, regardless of the camera's tape format. This is fine for small, low-resolution printouts. But if you want to create a press kit or other printed materials, be sure to take production stills with a film camera or a high-quality digital still camera.

Is there visual picture info in the "Missing Lines" ??  YES !!

The every other line that is missing in a field, is contained in the other field - remember one frame is comprised of a pair of fields (called odd and even). 

These lines are not part of the field, since a field . . . by its very definition, has only odd lines . . . or even lines.

But they are not completely missing either.  At least not when you export to an image.  I am not sure why, but there are only 2 possible explanations:

• the video file itself contains filler data for the missing lines
• Premiere fills in the lines when it exports with some data - even though it is not truly "de-interlacing"

The computer image display is NOT filling in pixel data for those lines, as it is capable if showing an image where every other line is missing (i.e. a black or white line).

This may be a direct export of the "actual field" stored in the video file - and you can see by all the test samples below, that even though this is not yet de-interlaced, the image does have some "related data in the missing lines".  Otherwise you would see straight horizontal lines, such as black or white lines, as we have created below in Photoshop to simulate what that would look like and to prove that Premiere or the Video file itself DOES have data in the "missing lines".  The pics below are blown up 200%, so each line is actually 2 pixels tall (2 lines) just so you can see it easier:

The Fix:  De-Interlacing

Here we show you two methods of de-interlacing an exported still image. Both fixes are simple but both are also far from perfect.  You cannot recreat missing data, and a field is only 1/2 of a frame !!  Every other line is simply not there.  De-interlacing in Photoshop can be done with two ways:

• Duplicate - simply take every other line, and make an exact copy, filling and overwriting the line below
• Interpolate - makes the "best guess" by interpolating both adjacent lines to each missing line, and fills it in.

An exported frame from Premiere is really only one of the two fields from that frame.  So it results in an image that contains only half of the lines.  Premiere exports one instant in time - and it views that as a field, since the captured video is interlaced.  Here is a small section of an exported frame, magnified.  You can see the effect of interlacing, especially on the edges where the "fringing" effect can be seen.  Note that these lines are missing information, since the field that contains them is not present (see the fringing all along the left and right edges of the black text). 

So Premiere does fill in "some" missing info, somehow - or maybe the info is in the video file itself - not sure.  This creates a messy but related set of pixels going across each "missing line".  But it is a mess !!!

Comparison of the two Methods

DO NOT USE PREMIERE DE-INTERLACE !!!

*** as you can see . . . at least with my tests, the Premiere "de-interlace" simply DOES NOT WORK AT ALL !!!  This was done using Premiere v6.5 and a valid NTSC interlaced video file (720x480 DV AVI), so I cannot speak for the other versions of Premiere, but this is not working.  So use Photoshop !!!

Method 1 (preferred) - use Photoshop's De-Interlace Filter

(export normally with Premiere)

Open the image in Photoshop, and select:  Filter/Video/Deinterlace  -  which yields the following:

Photoshop simply takes every other line, and replaces the lines in between with an interpolation of the two adjacent lines.  The lines that are replaced are the ones missing data (from the missing field).  The tiny white lines where there should have been black text are now filled in with black.  Surprisingly, it does not make any difference whether you select Even or Odd field with the deinterlace filter.  I tried both and the results are identical !!

But you can recreate data precisely when the data is not there - so this is not the best way, and as you can see, the edges of the lettering are not very sharp.  If you want high quality images, then use a digital camcorder - or a PC card/Memory stick with your camcorder.

Method 2 - use Premiere's De-Interlace Function

If you export a video frame as a still image from Adobe Premiere 5.0 or later, horizontal lines appear in the image. The lines appear even if you selected Deinterlace in the Special Processing Options dialog box.

In the Field Options dialog box, set the Processing Option for the clip to Always Deinterlace and then export the frame from the Timeline:

1. If the clip containing the frame you want to export is not in the Timeline, drag it there.

2. Select the clip in the Timeline, and choose:

• Clip > Video > Field Options (Premiere 5.x)
• Clip > Video Options > Field Options (Premiere 6.x and Pro)

3. Select Always Deinterlace in the Processing Options section of the Field Options dialog box, and then click OK.

4. either in the "Source" monitor window, forward or reverse the clip to get to the frame you want to export

5. File > Export Timeline > Frame (Premiere 6.0x)

    File > Export > Frame (Premiere 5.x).

6. Enter a name and location for the exported frame, and then click OK.

Additional Information

The Field Options settings override the Special Processing Options settings when you export still images or movies from Premiere.