Redrushes Crop Math

[Jordan Livingston]

Dear RED Experts,

This is a plea for some math help in determining proper crop settings in REDrushes.

- I'm working with 4K footage shot in the full 2:1 aspect ratio.

- The content was framed for a 1.85:1, center-cut.

- My Debayer setting is "Half Res (High)"

- My final output is a [slightly] matted 1920x1080 (16:9) ProResHQ file.

My "scale" settings are set to 1920x1080, "Fit Width," but I have been unable to figure out what the proper crop settings should be.

I have calculated that the desired 1.85:1 image area within the 2:1 4K frame is 3789x2048, however, I've been told that the "crop" settings are actually based on Debayer quality setting; so I'm not sure what the "Half Res" equivalent would be.

I'm also completely clueless as to how one calculates the "Origin X" and "Origin Y" settings.

Thanks very much in advance to anybody who can help me with this procedure!

 

[Conrad Hunziker]

R3D Data Manager's Quicktime renders does all the math for you, and is optomized for batch renders. Just select your options and render.

 

[Jordan Livingston]

R3D Data Manager's Quicktime renders does all the math for you, and is optomized for batch renders. Just select your options and render.

This program is awesome and I will definitely utilize it... However, if I'm being a cheapskate, er, I mean, if I want to learn the underlying math - does anybody know how I could calculate these settings on my own?

 

[Uli Plank]

Use Clipfinder, you cheapskate ;-)

 

[Hans-Georg Daun]

The resolution of a clip shot at 4K 2:1 debayered at 1/2 res high is 2048 x 1024.

You cannot get a height of 1080 from this by matting.

If you want to avoid upscaling, you need to debayer at full res, crop to 3789 x 2048, then scale to 1920 x 1080.
The crop settings for a center crop work out as
Origin X: (4096-3789)/2 = 154
Origin Y: 0
Width: 3789
Height: 2048

If you don't mind the upscaling, then crop to 1895 x 1024 for a 1.85:1 aspect. The crop settings (again for a center crop) are now
Origin X: (2048-1895)/2 = 75
Origin Y: 0
Width: 1895
Height: 1024

I hope this helps.
Let me know if you need more info.

Cheers,
Hans

Dear RED Experts,

This is a plea for some math help in determining proper crop settings in REDrushes.

- I'm working with 4K footage shot in the full 2:1 aspect ratio.

- The content was framed for a 1.85:1, center-cut.

- My Debayer setting is "Half Res (High)"

- My final output is a [slightly] matted 1920x1080 (16:9) ProResHQ file.

My "scale" settings are set to 1920x1080, "Fit Width," but I have been unable to figure out what the proper crop settings should be.

I have calculated that the desired 1.85:1 image area within the 2:1 4K frame is 3789x2048, however, I've been told that the "crop" settings are actually based on Debayer quality setting; so I'm not sure what the "Half Res" equivalent would be.

I'm also completely clueless as to how one calculates the "Origin X" and "Origin Y" settings.

Thanks very much in advance to anybody who can help me with this procedure!

 

[Jordan Livingston]

If you want to avoid upscaling, you need to debayer at full res, crop to 3789 x 2048, then scale to 1920 x 1080.
The crop settings for a center crop work out as
Origin X: (4096-3789)/2 = 154
Origin Y: 0
Width: 3789
Height: 2048

Hans,

This is very helpful - thank you!

My only remaining question pertains to the "origin" setting. If I leave the origin field blank, doesn't that dictate a center cut, with equal portions chopped from the left and right sides? I guess I'm not exactly sure what the origin fields are defining.

 

[Steve Freebairn]

No, origin is calculated from the upper left, where 0,0 is the upper left.

 

[Jordan Livingston]

Another user just suggested a slightly different approach via a private message:

His recommendation was to set debayer resolution to "full," scale to 1920x1080, and opt for "fit height."

The resulting image would be inherently center-cut 16:9, however, the 1.85:1 matte could be added later in Final Cut Pro, allowing me a few extra pixels to adjust the image up and down, which can be useful to have anyway.

I guess it makes a lot more sense to simply avoid the complex scaling math in REDrushes, and just add the mattes later... Does anybody disagree with this approach?

 

[Jordan Livingston]

Another user just suggested a slightly different approach via a private message:

His recommendation was to set debayer resolution to "full," scale to 1920x1080, and opt for "fit height."

The resulting image would be inherently center-cut 16:9, however, the 1.85:1 matte could be added later in Final Cut Pro, allowing me a few extra pixels to adjust the image up and down, which can be useful to have anyway.

I guess it makes a lot more sense to simply avoid the complex scaling math in REDrushes, and just add the mattes later... Does anybody disagree with this approach?

Upon further testing, while this method does yield a 1.85:1 matted image within a 16x9 HD frame, it doesn't actually preserve the true 1.85:1 framing (within the 2:1 field) that the DP intended. Looks to me like the methods described by Hans above are indeed the best way to go here...

- Jordan