Display system with switchable aspect ratio

• US 5,638,130 A
• Filed: 05/25/1995
• Issued: 06/10/1997
• Est. Priority Date: 05/25/1995
• Status: Expired due to Term

• Current Assignee: Mitsubishi Electric Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Linzer, Elliot N.
• Primary Examiner(s): Kostak, Victor R.
• Application Number:
  US08/450,196
• Time in Patent Office: 747 Days
• Field of Search: 348/445, 348/556, 348/441, 348/705, 348/706, 348/913, 348/904
• US Class Current: 348/445
• CPC Class Codes: H04N 19/85 using pre-processing or post-processing specially adapted for video compression
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 21/440272 for performing aspect ratio conversion
• CPC Class Codes: H04N 21/4858 for modifying screen layout parameters, e.g. fonts, size of the windows
• CPC Class Codes: H04N 7/0122 the input and the output signals having different aspect ratios

Abstract

A system and method for receiving a video sequence with a given aspect ratio and displaying that sequence on a device with a different aspect ratio in letterbox form by performing letterbox type conversion immediately before display. In letterbox form, the viewer sees the entire active region of the picture but the whole screen is not used. In one embodiment a video sequence with a given aspect ratio can be displayed on a device with a different aspect ratio in letterbox or pan-scan form, at the users discretion, by performing, respectively, letterbox or pan-scan conversion immediately before display. Thus, the user can decide to use the entire screen or to see the entire picture.

Claims

1. A system for displaying a received a video sequence with a given display aspect ratio on a display device having a different display aspect ratio, wherein the video sequence comprises a number of frames of the given display aspect ratio having a first number of pixel columns and a second number of pixels rows, comprising:

a video decoder connected to receive the video sequence;

a letterbox subsystem, connected to received a decoded version of the video sequence from the video decoder, the letterbox subsystem including;

frame scaling means for applying frame-based scaling to the frames so as to produce an output frame with the given display aspect ratio but having only one of the number of rows or the number of columns equal to the number of rows or columns in the intended display;

field scaling means for applying field-based scaling to the frames so as to produce an output frame with the given display aspect ratio but having only one of the number of rows or the number of columns equal to the number of rows or columns in the intended display;

a multiplexor coupled to the frame scaling and the field scaling means, for selectably providing at its output the output frame from one of the field scaling means and the frame scaling means responsive to whether the frame is interlaced;

frame padding means connected to receive the output from the multiplexor for unit, for padding the frame so as to fill the entire display area;

and,

a display device connected to receive an output of the letterbox subsystem;

wherein the letterbox subsystem converts the video sequence into a format in which each picture can be viewed in its entirety without filling the entire viewing area of the display device.

2. A system for displaying a received a video sequence with a given display aspect ratio on a display device having a different display aspect ratio, comprising:

a video decoder connected to receive the video sequence;

a letterbox subsystem coupled to the video decoder, the letterbox subsystem including;

frame scaling means for applying frame-based scaling to the frames so as to produce an output frame with the given display aspect ratio but having only one of the number of rows or the number of columns equal to the number of rows or columns in the intended display;

field scaling means for applying field-based scaling to the frames so as to produce an output frame with the given display aspect ratio but having only one of the number of rows or the number of columns equal to the number of rows or columns in the intended display;

a multiplexor coupled to the frame scaling and the field scaling means, for selectably providing at its output the output frame from one of the field scaling means and the frame scaling means responsive to whether the frame is interlaced;

frame padding means connected to receive the output from the multiplexor for unit, for padding the frame so as to fill the entire display area;

a pan-scan subsystem coupled to the video decoder;

a display device; and

,

a multiplexor coupled to the letterbox subsystem and the pan-scan subsystem, the multiplexor being responsive to a user initiated control signal for sending one of an output of the letterbox subsystem and an output of the pan-scan subsystem to the display device;

wherein a user can selectably control whether the video is to be displayed in a letterbox format in which each picture can be viewed in its entirety without filling the entire viewing area of the display device or a pan-scan format in which a portion of each picture in the video sequence is displayed on the entire viewing area of the display device.

3. A method of displaying a compressed video sequence with a given display aspect ratio on a display device having a different display aspect ratio, comprising the steps of:

(a) decoding the compressed video sequence to produce a decoded video sequence;

(b) responsive to a control signal, converting each frame of the displayable video sequence into one or letterbox format or pan-scan format; and

(c) displaying least some of the frames produced by the converting;

wherein the converting to a letterbox format comprises the steps of, for each frame;

(d) calculating an input display aspect ratio as the product of a sample aspect ratio of the frame to be displayed and a number of columns and a number of rows in the frame to be displayed;

(e) calculating an output display aspect ratio as the product of the sample aspect ratio of the display device and the number of rows and number of columns displayable on the display device;

(f) calculating the number of rows and number of columns to be displayed on the display device as a function of the input display aspect ratio and the output display aspect ratio;

(g) determining if the frame is interlaced;

(h) when it is determined that the frame is not interlaced, scaling the frame if the frame using frame based scaling such that a resulting scaled frame has a sample aspect ratio equal to the sample aspect ratio of the display device the number of rows and columns calculated in step f;

(i) when it is determined that the frame is interlaced, scaling each field of the frame such that resulting fields have sample aspect ratios equal to the sample aspect ratio of the display device and either half the number of columns or half the number of rows calculated in step f, and combining the resulting fields to form the scaled frame; and

,

(j) padding the scaled frame, so that it has the same number of columns and the same number of rows as the display device.

4. A system for displaying a compressed video sequence with a given display aspect ratio on a display device having a different display aspect ratio, comprising:

means for decoding the compressed video sequence to produce an displayable video sequence;

means, responsive to a user initiated control signal, for converting each frame or the displayable video sequence into one or letterbox format or pan-scan format; and

means for displaying the frames produced by the converting;

wherein the means for converting comprises;

means for determining if each frame is interlaced;

logic means for (a) when it is determined that a frame is not interlaced, scaling the frame if the frame using frame based scaling such that a resulting scaled frame has a sample aspect ratio equal to the sample aspect ratio of the display device and either the same number of columns or the same number of rows as the display device; and

(b) when it is determined that the frame is interlaced, scaling each field of the frame such that resulting fields have sample aspect ratios equal to the sample aspect ratio of the display device and either the same number of columns or half the same number of rows as the display device, and resulting fields to form the scaled frame; and

,

means for padding the scaled frame, so that it has the same number of columns and the same number of rows as the display device.