Open-Gate Crop Calculator

What open gate actually records

Open gate means the camera reads out its full active sensor area with no in-camera aspect crop baked in — no 16:9 or 17:9 window applied at capture. The ARRI ALEXA 35 in open-gate mode records the whole 4608×3164 photosite array (≈1.46:1), the ALEXA Mini LF records 4448×3096 (≈1.44:1), and Panasonic's S1H, S5IIX, GH6 and GH7 read out their full 3:2 or 4:3 sensors. None of those shapes match a delivery spec on their own — which is the point. Open gate captures the maximum pixels the sensor can give you, and every deliverable aspect is a crop decided in post, not a limitation baked in on set.

That workflow became standard because delivery lists stopped being one aspect ratio. A single production now routinely owes a broadcaster or theatrical DCP a 2.39:1 or 16:9 master, a streaming platform a 16:9 (sometimes 4:3-protected) version, and social cutdowns at 9:16, 1:1 and 4:5. Shooting each of those separately means either multiple takes or committing to one crop on set and losing the others. Shooting open gate and cropping every aspect from the same original negative keeps every deliverable framed from full resolution and lets editors and colorists make the crop call with the whole frame in front of them.

The largest-fit crop math

For a sensor of W×H and a target aspect t = tw/th, the largest crop of that aspect that fits inside the sensor is found by comparing the sensor's own aspect W/H against t:

• If W/H > t (the sensor is proportionally wider than the target), the crop is height-limited: it takes the full sensor height and crops the sides — width = H × t, height = H. This is a pillar crop.
• Otherwise the crop is width-limited: it takes the full sensor width and crops top and bottom — width = W, height = W ÷ t. This is a letter crop.

Both crop dimensions are then rounded down to the nearest even integer, because H.264, H.265 and most delivery codecs sample chroma in 2×2 blocks and reject or silently pad odd dimensions.

Worked examples — ARRI ALEXA 35 open gate, 4608×3164 (W/H ≈ 1.4563):

• 16:9 (t ≈ 1.7778): sensor aspect (1.4563) is narrower than 16:9, so the crop is width-limited — full width, letter-cropped: 4608 × (4608 × 9 ÷ 16) = 4608 × 2592. Retained = 2592 ÷ 3164 ≈ 81.9% of the frame height (and of the sensor area, since width is unchanged).
• 9:16 (t = 0.5625): sensor aspect is wider than 9:16, so the crop is height-limited — full height, pillar-cropped: height 3164, width 3164 × 9 ÷ 16 = 1779.75, floored to the nearest even integer → 1778. Crop is 1778 × 3164. Retained area = (1778 × 3164) ÷ (4608 × 3164) = 1778 ÷ 4608 ≈ 38.6%.
• 1:1 (t = 1): height-limited again — height 3164, width 3164 (already even). Retained = 3164 ÷ 4608 ≈ 68.7%.

Reading the retained-% column

"Retained" is the crop's area as a percentage of the full open-gate sensor area — not a comparison to any one delivery resolution. A 9:16 crop retaining 38.6% of an ALEXA 35 frame means you are delivering roughly a third of the pixels the sensor captured; the other two-thirds (the left and right thirds of frame) are gone in that master. That number is the reason vertical cutdowns from a widescreen-composed open-gate shoot often look cramped: if the frame was composed for 16:9 with subjects spread across the width, a 9:16 pillar crop from the same negative throws most of that composition away. Reading this column before the shoot — not after — is what lets a DP frame with the tallest deliverable's crop line in mind from the start.

The min-delivery warning logic

Each target aspect is checked against the standard delivery rasters a platform actually asks for — 16:9 against 3840×2160 (UHD) and 1920×1080; 9:16 against 1080×1920 and 2160×3840; 1:1 against 1080×1080; 4:5 against 1080×1350; 2.39:1 against 4096×1716. A crop covers a raster only if it is at least as large as that raster in both dimensions — anything smaller in either dimension needs upscaling to fill the deliverable, which softens detail and can show interpolation artifacts. The ARRI ALEXA Mini LF is the example worth memorizing: its open-gate 9:16 crop is 1740×3096. That comfortably covers 1080×1920 (both dimensions larger), but it needs upscale for 2160×3840 because 3096 is short of 3840 — a 4K-vertical delivery from that camera's open-gate mode cannot be a native downscale; it has to be upscaled from a genuinely smaller crop, and the planner flags that before it becomes a delivery-day surprise.

Practical guidance

Shoot for the tallest (most cropped) deliverable on your list, not the widest — pillar crops for 9:16 or 1:1 lose the most area, so protect action and graphics within that narrowest safe zone even when framing wide for the primary 16:9 or 2.39:1 master. Build in a small safety margin beyond the tightest crop box for reframing and stabilization in post. Always round crop dimensions down to even numbers before locking them into an export preset — a codec that rejects 1779px wide will pad or reject the export outright. And remember the standard-raster list above comes from real distribution specs (Netflix, YouTube, Meta and broadcast delivery documents each publish their own), so treat it as a starting checklist, not a substitute for the actual spec sheet on a given job.

1. Choose your camera's open-gate recording mode, or type in the full-sensor pixel dimensions yourself.

2. Add every aspect you owe — 16:9, 9:16, 1:1, 4:5, 2.39:1, 4:3 or a custom ratio.

3. Compare each crop's resolution and percentage of frame retained against the delivery rasters in the UHD vs DCI 4K Resolution Chart.