Anamorphic Desqueeze: Squeeze Factors and Aspect Ratios

What the squeeze does

An anamorphic lens compresses the image horizontally by a fixed factor, its squeeze, and leaves the vertical alone. A 2× lens fits twice the horizontal field of view onto the same sensor width, so the recorded picture looks tall and thin. Stretching it back out by the same factor, the desqueeze, restores normal proportions and gives a much wider frame than the sensor's own shape.

The arithmetic is simple. What makes it worth a guide is choosing the squeeze and sensor area that land on your delivery ratio, usually 2.39:1, without throwing away more of the sensor than you need to, and then getting the desqueeze right in every step of post.

Desqueeze formulas

Squeeze factor by sensor shape

Desqueezed aspect ratio for each common squeeze on each common recording shape. Results within a few hundredths of 2.39 need almost no crop for a scope finish.

A result wider than your delivery ratio is cropped at the sides; a narrower one is cropped top and bottom. Either way, the crop is pixels you recorded and then threw away, so the best pairing is the one closest to the delivery ratio.

Which squeeze for which sensor

• 2× on a 6:5 area gives 2.40:1, the classic scope pairing. The tall sensor modes cameras offer for anamorphic exist for this.
• 2× on 4:3 gives 2.67:1, so about a tenth of the width is cropped for 2.39.
• 1.8× on 4:3 gives 2.40:1 with almost no crop.
• 1.33× on 16:9 gives 2.36:1 (2.37 with an exact 4/3 squeeze), close enough to 2.39 that almost all of a standard 16:9 sensor area is used, which makes 1.33× a natural fit for cameras without a tall mode.
• 1.25× on 17:9 gives 2.37:1, the same idea on a DCI-width sensor area.
• 1.5× on 3:2 gives 2.25:1, a little taller than scope; a 1.5× lens on a 16:9 area gives 2.67:1.
• 1.65× on an Open Gate 3:2 area lands on 2.39:1 inside the frame: ARRI's guideline frames 4348 × 3006 of the ALEXA 35's 4608 × 3164 for it.

The ALEXA 35 alone accepts squeeze settings of 1.25, 1.30, 1.33, 1.50, 1.66, 1.80, 1.85 and 2.0, so check the exact factor your lens is specified at: a 1.3× and a 1.33× lens give different ratios, and the desqueeze has to match the glass.

Anamorphic sensor modes

Cameras built for anamorphic offer taller recording areas so a 2× lens fills them without cropping. The ALEXA 35, a 4.6K Super 35 camera, is a good example because ARRI publishes the figures for every mode.

Other makers offer similar modes under their own names. Whatever the camera, the test is the same: the recorded area's width ÷ height × squeeze should be at or just above your delivery ratio, and the lens has to cover the area. ARRI's guideline warns that some 1.65× lenses may not fully cover the Open Gate area, so test illumination before you commit.

Desqueezing in post

The recorded file is squeezed; every viewer of it needs the desqueeze. Most cameras write the squeeze to the metadata, and most grading and editing software reads it, but check: if it is not picked up, set the pixel aspect ratio or desqueeze factor by hand to the lens's squeeze.

Stretch or squash

You can desqueeze either way. Stretching the width by the squeeze keeps every vertical line: 3328 × 2790 at 2× becomes 6656 × 2790. Squashing the height keeps every horizontal photosite: the same frame becomes 3328 × 1395. Both are the same picture; the first is usual for finishing, the second can be useful for lightweight dailies.

Scaling to the deliverable

Scale the desqueezed active area to the delivery width and check the height. From the 2996 × 2512 frame line: 2996 × 2 = 5992 wide, scaled by 4096 ÷ 5992 = 0.684 to 4096 × 1717, which trims a line to the 1716 of DCI Scope. Shoot a framing chart or leader with the frame lines, and send it to everyone in post so dailies, editorial, VFX and the finish all frame the same way.

Delivery resolutions and letterboxing

In digital cinema, “2.39:1” means the DCI Scope container: 4096 × 1716 at 4K and 2048 × 858 at 2K, both 2.387:1. In a 16:9 container the scope image sits between black bars; the aspect ratio cheat sheet lists the bar sizes for common ratios in HD and UHD.

Streamers and broadcasters set their own rules for scope titles, including whether they want the bars in the file at all. Read the delivery spec before you render. The free aspect ratio calculator works out the image size and bars for any ratio and container in your browser, and the DCP guide covers Scope and Flat packages.

The Anamorphic calculator

CineMath's Anamorphic calculator does the desqueeze math for any lens and sensor area. Choose a squeeze (1.25, 1.33, 1.5, 1.8 or 2.0×, or type your own, such as 1.65), enter the sensor width and height and the focal length, and it gives the recorded ratio, the desqueezed ratio, the desqueezed width and the horizontal-equivalent spherical focal length, with the formula and your numbers in it. The free anamorphic calculator does the same in your browser.

The desqueezed ratios above are the exact values the result line gives in brackets, to two decimals; the label on the result card can round to a nearby named ratio instead. The second row shows why a 1.33× lens on a 16:9 area is a near miss for 2.39 rather than an exact fit.

This describes CineMath 1.3, the next update. Until it reaches the App Store, the version there is 1.2.1, and the Anamorphic screen differs in places.

Next steps

• Put your own squeeze and sensor area into the free anamorphic calculator, in your browser.
• Compare a 2× anamorphic frame with a spherical 2.39 extraction in anamorphic vs spherical.
• Check the horizontal and vertical angle of view with the Field of View calculator, which has its own squeeze setting.
• Size letterboxes and crops for any ratio with the Aspect Ratio calculator.

Before the lens test, put your sensor mode and squeeze into CineMath's free Anamorphic calculator and see the ratio you will actually finish at.