Do you need to Deinterlace when Downscaling Progressive Video?

[VideoFanatic]

I've got a video that was 1080i that was then re-encoded to 1080p 50fps. I'm then downcaling the 1080p video to 720p. Do I need to deinterlace to prevent artifacts?

[Sharc]

No

[LMotlow]

Why would you deinterlace progressive video? Progressive video isn't interlaced.

[pandy]

I'm downcaling a video from 1080p to 720p. Do I need to deinterlace to prevent artifacts?

Yes, de-interlacing interlaced content is mandatory if your intention is to resize video (in vertical direction, interlaced aware horizontal resize is usually safe). There is only one special exception if you reducing vertical size exactly by half then you efficiently performing de-interlacing and resize at the same time (this type of resize is sometimes called line blending).

Btw if your content is progressive then you don't need to de-interlace it before resize (it is not clear to me what is your source as naming convention suggest that this is 1080 progressive i.e. not interlaced).

[jagabo]

Sometimes you get interlaced video that has been encoded progressive (because someone didn't know what they were doing). Those need to be deinterlaced before downscaling.

[VideoFanatic]

Thanks. To be more clear, my video was 1080i that was then re-encoded to 1080p 50fps (it's definitely progressive). I'm then downcaling the 1080p video to 720p. Do I need to deinterlace to prevent artifacts?

[Sharc]

So as I understand the original 1080i25 has already been bob-deinterlaced to 1080p50. No, don't deinterlace the 1080p50 for resizing to 720p.

[pandy]

Thanks. To be more clear, my video was 1080i that was then re-encoded to 1080p 50fps (it's definitely progressive). I'm then downcaling the 1080p video to 720p. Do I need to deinterlace to prevent artifacts?

So you already de-interlaced (i.e. converted interlaced source to progressive).