Neat Blog

Interlaced video. Nuances of denoising

Have you got a squished and stretched image inside Neat Video’s window? Or maybe even two such images one above another? There is nothing wrong with your footage or Neat Video and your denoised video will not look anything like that. It just means that you are likely working with interlaced footage.

Video scan types

Interlaced and progressive scan types are used in two corresponding formats of a video representation.

A progressive video clip contains a set of frames, each of which shows the whole image of the scene, with all its scan lines present in each frame.

An interlaced video clip on the other hand shows odd and even scan lines as two separate images, or fields also displayed at different moments in time. Typically, the field with the odd scan lines is displayed first, and then, a bit later, the field with the even scan lines is displayed.

Such two fields are usually called “upper field” (odd scan lines) and “lower field” (even scan lines).

Essentially, interlaced video is a stream of pairs of upper and lower fields. One second of a 60 FPS interlaced video contains 30 upper and 30 lower fields. As mentioned above, the upper and lower fields are displayed at slightly different times, with a very short delay in between. Because the delay is very short, our eyes see the result as a whole frame and not as two separate sets of scan lines with gaps between them.

Interlaced video format is traditionally used in broadcasting as such video can be transmitted more efficiently, with less required bandwidth, as compared with a progressive format.

The downside of interlaced format is that it can result in a “comb” effect and make the image seem blurry in scenes with fast motion.

That happens because each field is captured at a slightly different time and, if the object in the scene is moving fast, then it appears in different positions in consecutive odd and even fields. For example, moving cars, sport players, planes on the runway, etc. can appear blurry or have motion artifacts if filmed in interlaced format.

A progressive format, on the other hand, captures the whole picture in a single frame at one moment in time. Hence it shows no temporal artifacts that are typical for interlaced video.

How to find out the scan type of a clip

Not every video editing software or video player can provide you with the information on the scan type. One of the universal ones that work on Windows, macOS, Linux Mint, Ubuntu, Android and many others is MediaInfo. Once downloaded, start the program, click < Click here to select file > and, as the name suggests, select the file you’d like to check.

MediaInfo will show the file’s metadata. You are after Scan type. Scan order is also important for interlaced video.

General recommendations for denoising interlaced video

Generally, it is best to apply Neat Video noise reduction to the original video data (be it interlaced fields or progressive frames), not to the data that have been converted from one scan type to another (deinterlacing).

For the best quality noise reduction try sticking with one scan type throughout a project. So if you have interlaced source clips, then your project/timeline/sequence should probably be also interlaced whenever possible.

When you can choose the point in the workflow where you change the scan type (if you have to change it), then choose to change it at a later stage, already after Neat Video is applied to the video, or even after the video with Neat Video applied has been exported (in interlaced format). This way you can let Neat Video work with the interlaced video data and denoise that data in its original interlaced format. This can avoid the potential loss of noise reduction quality that may be caused by using the converted (deinterlaced) data.

When working with interlaced clips and projects, also make sure the scan order (or field order) of the clip and the project/sequence are matching, otherwise, the final video will be twitching. The field order of the clip can be determined with the help of the MediaInfo app. The field order of an interlaced project/sequence can be adjusted in most video editing software (more on that below) to match that of the source clip.

Premiere Pro and interlaced clips

How does interlaced video look in the Neat Video window? You will see a single stretched image (for example, 1920x540 for a fullHD clip). That is a single field displayed with no gaps between scan lines.

How does interlaced video look in Premiere Pro viewer?Depending on the field settings of the viewer, you will either see one field (upper or lower) or two fields combined. In the case of one field, the image will be stretched vertically to the size of the frame (1920x1080 for a fullHD clip).

If the viewer is set to show both fields and you are working on a clip with rapid movement, the picture in the program monitor may show the “comb” effect and moving objects may appear blurry. 

How to check scan type in Premiere Pro?
 
If you want to check the scan type of a clip in Premiere Pro, you need to add Field Order and/or Video Field Order details to Headings in the Project Panel.

To do that, select a clip in the Project Panel, then move over Headings and right-click, select Metadata Display… In the search box type “Field”, which will leave you with “Field Order” and “Video Field Order”, select both. The operation above will add two extra columns to the Headings: “Field Order” and “Video Field Order”. To see them scroll all the way to the right.

Note: you can change the order of the Headings in the Project Panel to suit your individual needs by drag-and-dropping them to the required position. 

How to set a sequence to work with interlaced video in Premiere Pro?When a new sequence is created by adding a clip to the timeline, the Fields (scan type and scan order) are going to be set to match the properties of the clip. That is the easiest way. It is also possible to manually adjust the scan type and scan order in the Sequence settings. 
Special settings in Neat VideoSpecial settings in Neat VideoNeat Video receives data about the scan type from Premiere automatically. No need to make manual adjustments in Neat Video. 

DaVinci Resolve and interlaced clips

How does interlaced video look in the Neat Video window? You will see a deinterlaced frame (1920x1080 for a fullHD clip).



As you can see, it’s very hard to tell whether you are working with an interlaced video unless you know it or you have checked it using MediaInfo or Resolve’s Media tab (more on that below).

 

How does interlaced video look in Resolve viewer? Resolve always shows a deinterlaced frame in its viewer. Resolve itself applies deinterlacing to show a progressive frame in preview instead of showing an interlaced field or fields. 
How to check scan type in Resolve? Switch to the Media tab and check the Metadata panel. The Field Dominance will either show Progressive (for progressive scan type) or Upper Field/Lower Field for interlaced video. 
How to set a project and timeline to work with interlaced video in Resolve? Tick “Enable Interlace Processing“ in the project and timeline settings.
(In older Resolve 16, the option was called "Video field processing". However, it was not working properly there and it was better to leave it disabled and just set the scan type to "Interlaced" in Neat Video itself.) 
Special settings in Neat Video The scan type has to be manually set to “Interlaced” in the Neat Video window

Final Cut and interlaced clips

How does interlaced video look in the Neat Video window?            In Neat Video for Final Cut (SR), you will see a deinterlaced frame (1920x1080 for a fullHD clip).


In Neat Video for Final Cut (Standard Version), you will see a single field (1920x540 for a fullHD clip) with no gaps between lines.
How does interlaced video look in Final Cut? By default, Final Cut’s viewer shows a deinterlaced frame. To see both fields in the viewer, select View > Show In Viewer > Both Fields (this will show the “comb” effect in scenes with rapid movement). 
How to check scan type in Final Cut? Open Inspector and find Width x Height | FrameRateS. You will see FrameRateS, where S=”p” for progressive and S=”i” for interlaced. 
How to set a project to work with interlaced video in Final Cut? If you are creating a new project based on a clip, then Final Cut will match project settings to the properties of the clip. Alternatively, go to Inspector > Info > Modify and change Video and Rate settings to match those of the clip or otherwise according to your needs.
Special settings in Neat Video Neat Video receives data about the scan type from FCP automatically. No need to make manual adjustments in Neat Video. 

Vegas and interlaced clips

How does interlaced video look in the Neat Video window?       You will see a single field (for example, 1920x540 for a fullHD clip) with no gaps between lines.
How does interlaced video look in Vegas? You will either see two fields combined (which results in the “comb” effect) or a deinterlaced frame (if the Scale Video to Fit Preview Window is switched on).
How to check scan type in Vegas? By default, Vegas sets projects to match properties of a clip. You can change project properties manually as well. To do that click the gear icon in the left top of the viewer, go to the Video tab > Field order > select None (for progressive scan) or Upper field first / Lower field first (for interlaced scan).
How to set a project and timeline to work with interlaced video in Vegas? Go to menu File > Properties > Project Properties > Video > Field Order. Here you can select Upper Field first or Lower Field first for interlaced video (None is for progressive).
Special settings in Neat Video Neat Video receives data about the scan type from Vegas automatically. No need to make manual adjustments in Neat Video.

Most OpenFX and interlaced clips

How does interlaced video look in the Neat Video window? You will typically see two fields separated (for example, two fields of 1920x540 pixels each, displayed separately, one field over the other one).                                     


If the scan type in the Neat Video window is incorrectly set to Progressive, then you will see two fields combined and showing the “comb” effect.
How does interlaced video look in most OFX hosts? You will typically see two fields combined which results in the “comb” effect.
How to check scan type in OFX hosts? There is no standard way to check the scan type inside an OFX host application. We suggest using third party tools like MediaInfo.
How to set a project to work with interlaced video in OFX hosts?There is no standard way, but the OFX host application may offer a way to adjust the project settings to change the scan type there.
Special settings in Neat Video For correct processing you need to manually set the scan type to “Interlaced” in Neat Video window

VirtualDub and interlaced clips

How does interlaced video look in the Neat Video window?                 Each time you open Neat Video’s window after it’s applied to a clip, you will see a dialog asking you to specify the scan type of the current video clip as VirtualDub doesn’t send any scan type data to the plug-in.


If you choose ‘Interlaced' for an interlaced clip, then you will see two fields separated (for example, two fields of 1920x540 pixels each, for a fullHD clip, displayed one above the other).


In case you have incorrectly selected ‘Progressive’ while working with an interlaced video, Neat Video will show two fields combined , which results in the “comb” effect.


If by accident you have chosen an incorrect scan type, please switch to the right one (use the control in the lower left control of the Neat Video window) to achieve good filtration (denoise, deflicker, dust and scratch removal).
How does interlaced video look in VirtualDub? You will see two fields combined with the “comb” effect. Note: when the zoom is set to 50% the viewer will show one field, not two.
How to check scan type in VirtualDub? This depends on the decoder used in VirtualDub. If you are using the MPEG-2 plugin, go to File > File information… and check the scan type. Unfortunately, the native VirtualDub2 decoder won’t allow you to see the scan type of a clip, so you will need to either switch to a different decoder or use a separate tool like MadiaInfo.
How to set a project to work with interlaced video in VirtualDub?VirtualDub does not allow changing project settings to let plug-ins work correctly with interlaced video, so that task is left to plug-ins themselves. Plug-ins built to work with both interlaced and progressive scan types are able to process both types of video scan types even though they do not receive relevant scan type information from VirtualDub. Some plug-ins, including Neat Video, require users to manually specify the scan type of the current video clip.
Special settings in Neat Video As VirtualDub doesn’t send the denoiser any info about the scan type, Neat Video asks you to manually set the scan type to Progressive or Interlaced. It’s expected that you check the properties of the clip to make the right choice regarding the scan type.

Summary

We all sometimes convert the video from interlaced to progressive when working with originally interlaced footage but need to keep in mind that there is a chance of losing details along the way. Not every video editing application can do deinterlacing well, and sometimes we can be better off by keeping the scan type as is. In cases when you need to apply noise reduction and also have to change the scan type, it is a good idea to let noise reduction go first, at least with Neat Video. Otherwise, some data may be lost in the process of deinterlacing and that may result in worse filtration quality and further detail loss. Let Neat Video work on the original video data in its original format for the best results.