DCI Container & Masking
DCI 2K and 4K container sizes for Flat, Scope and Full, where non-standard aspect ratios sit inside them, and how much masking a cinema screen needs for each format.
DCI Containers
Every DCP picture sits in one of these image structures. Flat and Scope are the two standard presentation formats. Pixels are square, and 4K is exactly twice 2K in each direction.
| Format | Aspect ratio | 2K | 4K | Notes |
|---|---|---|---|---|
| Full container | 1.90:1 (1.896) | 2048×1080 | 4096×2160 | The whole image structure. Used for 1.90 deliveries such as IMAX digital. |
| Flat | 1.85:1 | 1998×1080 | 3996×2160 | Full height, 25 px (2K) or 50 px (4K) unused at each side. |
| Scope | 2.39:1 (2.387) | 2048×858 | 4096×1716 | Full width, 111 px (2K) or 222 px (4K) unused above and below. |
- Flat (dashed) uses the full height and nearly the full width.
- Scope uses the full width and 79 % of the height (858 ÷ 1080).
- A Scope DCP shown with no anamorphic lens therefore lights only 79 % of the imager rows. See the lens note below.
Other Ratios Inside the Containers
Content in a non-standard ratio is mastered inside a Flat, Scope or Full container with black bars. The figures show the largest image that fits each container (2K / 4K). The distributor decides which container to use, so check the DCP name or the delivery notes. Mastering facilities may round to even pixel counts, so actual sizes can differ by a pixel or two.
| Ratio | In Flat (1998×1080) | In Scope (2048×858) | In Full (2048×1080) |
|---|
1.43 is the IMAX 15/70 film and IMAX with Laser ratio. It is listed for information only, because standard DCI projection cannot show it at full size.
Screen Masking Calculator
| Format | Image W × H (m) | Side masks, each (m) | Top / bottom masks, each (m) | Screen used | Diagram |
|---|
Mask travel is measured in from the screen edge, assuming the image is centred. Many constant-width installations use a single top mask and keep the image bottom-aligned. In that case the top mask travels the sum of both figures. * This format doesn't fit the screen in the chosen mode, so it has been fitted inside the screen instead.
Anamorphic Lens vs Digital Scope
Digital scope (no anamorphic lens)
The projector shows the Scope DCP as delivered: 2048×858 inside the 2048×1080 imager, with the unused rows black. On a constant-height screen, a zoom lens with lens memory enlarges the image for Scope so that the picture fills the screen height. The black rows then spill onto the top and bottom masking.
- Only 858 of 1,080 rows (79 %) carry picture.
- The light from the unused rows is lost on the masking, so Scope is dimmer than Flat on the same screen.
- It is simple and cheap, and it is the most common setup.
Anamorphic lens
The projector stretches the 858 rows vertically to fill all 1,080 rows (×1.26, which is 1080 ÷ 858). An anamorphic attachment then expands the picture horizontally by the same factor to restore the 2.39 shape. The lens has to move out of the light path for Flat.
- The whole imager is used, so in theory there is about 26 % more light and resolution on Scope. The lens loses some of that light.
- It adds cost, alignment work and a motorised lens slide, and it can add slight geometric distortion.
Notes & References
- Container sizes come from the DCI Digital Cinema System Specification (image structure 2K 2048×1080 and 4K 4096×2160) and SMPTE ST 428-1 (D-Cinema Distribution Master: image characteristics). DCP packaging is defined in the SMPTE ST 429 series.
- Flat and Scope sizes (1998×1080 / 3996×2160 and 2048×858 / 4096×1716) are the standard presentation formats used throughout DCP mastering and in the ISDCF naming convention (F and S).
- The masking figures are geometry only. Check real installations against the masking track limits, the screen frame and the projector's lens memory positions.
- Related tools: Aspect Ratio Calculator and Projector Brightness Calculator (for the light lost on digital Scope).