FR3056872A1 - DIGITAL IMAGE PROCESSING AND PROJECTION METHOD FOR HOME BROADCAST - Google Patents

Abstract

According to an image processing and projection method for the diffusion in the cinema room, a calibration step is carried out in which an image sequence rendering processing is carried out adapted to a predetermined projector model, a step encapsulation method wherein the image sequences are supplemented with metadata to form a digital copy and a projection step in which the digital copy is projected by a projection system on a screen. In the encapsulation step, the metadata includes a data indicating that the calibration has been performed using a high dynamic process, the projection system reading said data and consequently selecting a first light amplification factor for a standard method or a second light amplification factor for the high dynamic process, the second factor being greater than the first factor.

Description

056 872

58969 ® FRENCH REPUBLIC

NATIONAL INSTITUTE OF INDUSTRIAL PROPERTY © Publication number:

(to be used only for reproduction orders)

©) National registration number

COURBEVOIE © IntCI ⁸ : H 04 N 9/79 (2017.01)

PATENT INVENTION APPLICATION

A1

©) Date of filing: 23.09.16. (© Applicant (s): YMAGIS Société anonyme - FR. (© Priority: @ Inventor (s): TO BE COMPLETED. ©) Date of public availability of the request: 30.03.18 Bulletin 18/13. ©) List of documents cited in the report preliminary research: The latter was not established on the date of publication of the request. (© References to other national documents ©) Holder (s): YMAGIS Société anonyme. related: ©) Extension request (s): (© Agent (s): GEVERS & ORES Société anonyme.

FR 3 056 872 - A1

DIGITAL PROCESSING OF IMAGE AND PROJECTION FOR BROADCASTING.

©) According to an image and projection processing method for broadcasting in cinemas, a calibration step is carried out in which a processing of image sequence rendering adapted to a predetermined projector model is carried out, an encapsulation step in which the image sequences are supplemented with metadata to form a digital copy and a projection step in which the digital copy is projected by a projection system on a screen. At the encapsulation stage, data is integrated into the metadata indicating that the calibration has been carried out according to a high dynamic process, the projection system reading said data and consequently selecting a first light amplification factor for a standard process or a second light amplification factor for the high dynamic process, the second factor being greater than the first factor.

DIGITAL METHOD OF BROADCASTING A FILM FOR INDOOR PROJECTION

FIELD OF THE INVENTION

The invention relates to a digital image processing and projection method for cinema distribution. It relates in particular to steps comprising a calibration of the image sequences, an encapsulation of said sequences with metadata and the projection of the film.

PRIOR ART

After having used the film support for a long time from the shooting to the projection in the cinema, the activity of the cinema has now passed entirely to digital format, which requires specific techniques for mastering the restitution of images. , in terms of color balance, contrast and brightness.

Projection systems convert a signal representing a so-called electric level into a light intensity. In modern digital projectors, this is achieved, for example, by a system of controlled micromirrors which i5 return a light source to the screen or elsewhere. The power returned is modulated by the duration of the light's return to the screen.

The difference perceptible to the human eye between two levels of illumination is a function of the light intensity and does not change linearly as a function of this intensity. For example, at a lighting power of 100 cd / m ² , the threshold perception is of the order of 1%, lcd / m ² , while at a lighting level of 0.01 cd / m ² , it is 10%, or 0.001 cd / m ² . Linear coding would require encoding at the weakest pitch, for example at 0.001 cd / m ² , which on a scale up to 100 cd / m ^{2 would} require 10 ⁵ values, ie coding on 17 bits. Also, we have chosen to encode the digital signal representing the light power to be projected by applying an encoding conversion and to restore the light power at the level of the projector by an inverse function performing a decoding function. The most common encoding function is a power function with a factor I / 7, followed by a decoding function with a power function of factor 7. We reach a correct quality with 12 bits of encoding per color in digital cinema.

The preparation of the distribution of a film goes through a calibration step, which consists of starting from the filmed sequences, to adjust the intensities of each of the three colors used for the projection in order to restore an image whose color balances and intensity are in accordance with the artistic intention of the author.

After the calibration step, a digital master source is obtained, referred to as DSM for "Digital Source Master". All the information necessary for the projection is gathered in an encapsulation step to provide a DCP (Digital Cinema Package) transport package which is based on a MXF (Material eXchange Format) file structure and an encryption system based on private and public keys for projection servers. This package is supplied to movie theaters where it is read by the projection system.

The DCI (Digital Cinema Initiative) recommendation, which has since been standardized by the SMPTE, defines the characteristics of a DCI certified projector and the projection conditions. The projector must have a contrast ratio of 2000 to 1 (2000: 1) and the white point is defined in the room at a value of 14 foot25 lamberts (fL) or 48 candelas per square meter (cd / m ² ). The encoding curve is based on a power function with a value of 1 / 2.6 for encoding. The restitution follows a power curve of 2.6.

These projection conditions do not currently allow images to be restored with high dynamic range, that is to say with a contrast greater than 2000 to 1.

Document US 9,288,499 B2 proposes a method of encoding and decoding the master source making it possible to maintain a high dynamic range. However, it is necessary that the projection system is equipped with a decoding program adapted to this encoding.

OBJECTIVES OF THE INVENTION

The invention aims to provide a digital method of broadcasting a film for projection in a cinema making it possible to preserve a high image dynamic, without however requiring significant modifications to the projection system defined by current standards.

DESCRIPTION OF THE INVENTION

With these objectives in view, the subject of the invention is a digital method of broadcasting a film according to which a calibration step is carried out in i5 which performs a rendering treatment of image sequences adapted to a model of predetermined projector, an encapsulation step in which the image sequences are supplemented with metadata to form a digital copy and a projection step in which the digital copy is projected by a projection system on a screen, characterized in that , in the encapsulation step, a datum indicating that the calibration has been carried out according to a high dynamic process is integrated into the metadata, the projection system reading said datum and consequently selecting a first light amplification factor for a standard process or a second light amplification factor for the high dynamic process, the second factor being greater than the first factor.

The method according to the invention operates on two stages of the diffusion of the film. At the calibration stage, the colors are encoded taking into account the level of brightness that will be used for the projection in order to respect the artistic intention of the director. Indeed, the projection of a film made for standard projection on a projection system with an amplification factor for high dynamics would give colors that are too bright and an image too clear. The specific calibration maintains an overall luminance level comparable to the classic version but uses the additional luminosity to emphasize the details and make certain parts of the image more saturated if necessary: fine details such as hair can be restored with more precision , the effects of explosions or light rays can be more dramatic. This can be implemented using existing hardware, adding to the level of the projection system taking into account the implementation of the method in order to perform the projection with the required level of brightness.

According to a preferred characteristic, the second factor is greater than 1.5 times the first factor, preferably 2 times the first factor.

i5 According to a particular provision, the projection system is adjusted so that a white point corresponding to the maximum light power is at a value greater than or equal to 100 cd / m ² . Depending on the distance from the projector to the screen and its power level, it may be necessary to supplement the projection system with one or more projectors to achieve the required light power, as already known per se in the field of digital projection.

Preferably, the film is projected in a room whose surfaces are treated in black. We thus limit the reflections towards the screen, which allows to obtain deeper blacks, and therefore to increase the perceived contrast. We are thus able to restore images with high contrast.

Preferably, the film is projected with a projector whose performance allows an inter-image contrast of at least 7000: 1. Despite the increase in the maximum luminance level, the depth of the blacks is respected. Inter-image contrast is defined by the level of luminance between two successive images, between a completely white image and a completely black image, with a colorimeter pointed towards the center.

BRIEF DESCRIPTION OF THE FIGURES

For a better understanding of the invention, reference is made to the following description and to the accompanying drawings, among which:

> Figure 1 is a schematic view of a method of diffusing a film according to the invention.

DETAILED DESCRIPTION io In an example of using the method according to the invention, the workflow complies with the ACES recommendations (Academy Color Encoding System). Figure 1 shows a diagram of this flow recommended by these recommendations and which is used in the invention.

According to this diagram, the data coming from the camera can i5 undergo an input transformation 1 called IDT (Input Device Transform) to convert the colors into a standardized color space and supply them to an ACES space 2. This conversion takes into account the behavior of the camera as well as for example of the lighting, according to whether it is natural or artificial, and according to the lighting technology.

The ACES 2 space allows for post-production of the film, including editing and a wide variety of treatments.

The result is then processed in a stream 3 which includes a calibration step 31 which can include a part of global film sequence processing by LMT (Look Modification Transform) filters and / or a part of localized processing of areas image, all under the control of a colorist. The result is taken in a rendering process which includes a first general rendering stage 311 RRT (Reference Rendered Transform) in order to produce a digital source master and a second specific rendering stage 312 ODT (Output Device Transform) to adapt the images to the device that will perform the projection. During the colourist’s work, the specific rendering step is adapted to a monitor or projector that the colourist uses to assess the result. After an encapsulation step, not shown, in which we receive the output of the specific rendering step adapted to the projector for which the film is intended, we obtain the digital copy which will be delivered to the projection room to be screened there. During the encapsulation step, according to the invention, data is integrated indicating that the calibration has been carried out according to a high dynamic process. The specific rendering steps, whether for the monitor or for projection in the room according to the method of the invention, are adapted to the method.

The projection system receives the digital copy, reads the metadata, and in particular determines whether the data indicating that the calibration has been carried out is according to a high dynamic process is present. In this case, the projection system applies a setting so that the surface power of the brightest point is multiplied by a factor greater than 2 compared to the standard setting.

The specific rendering step has taken this parameter into account so that a part of the image to be rendered at a predetermined luminance level has been encoded with a value divided by said factor compared to standard encoding, to be restored by the projector at the desired luminance level.

Thanks to the method according to the invention, the colorist has a larger color scale, making it possible to restore films with high dynamics, this with means requiring little adaptation of the existing material.

Claims (5)

Claims 1. Digital image and projection processing method for cinema distribution, according to which a calibration step is carried out in which image sequence rendering processing is carried out 5 adapted to a predetermined projector model, an encapsulation step in which the image sequences are supplemented with metadata to form a digital copy and a projection step in which the digital copy is projected by a projection system onto a screen, characterized in that, in the encapsulation step, there is integrated into the metadata a datum indicating that the calibration has been carried out according to a high dynamic process, the projection system reading said datum and consequently selecting a first light amplification factor for a standard process or a second light amplification factor for the high dynamic process, the second factor i5 being greater than the first factor. 2. The method of claim 1, wherein the second factor is greater than 1.5 times the first factor, preferably 2 times the first factor. 3. Method according to one of the preceding claims, according to which the 20 projection system so that a white point corresponding to the maximum light power is at a value greater than or equal to 100 cd / m ² . 4. Method according to one of the preceding claims, according to which the film is projected in a room whose surfaces are treated in black. 5. Method according to one of the preceding claims, according to which the film is projected with a projector whose performance allows an inter-image contrast of at least 7000: 1. 1/1 σ> LL