TW202007151A - Circuit and method of image compression - Google Patents

Abstract

An image compression circuit includes a least significant bit (LSB) processing unit configured to generate an LSB image; a splitter configured to split the LSB image into a plurality of single depth blocks; and a coding-and-selecting unit, configured to perform a lossless compressing encoding on a first single depth block to generate a first coded block, obtain a compression ratio according to the first single depth block and the first coded block, and determine whether the compression ratio is less than a specific value; wherein when the compression ratio is less than the specific value, the first coded block is stored into a buffer.

Description

Image compression circuit and method

The invention refers to an image compression circuit and method, in particular to an image compression circuit and method that can effectively compress low-efficiency bit images.

High Dynamic Range (High Dynamic Range) images can capture a wide range of brightness and have better visual effects, and have been used in systems such as digital TV. Compared with the traditional image, the high dynamic range image has more pixel bits, that is, the single pixel value in the image is represented by more pixel bits.

On the other hand, the digital TV system will store the image frame to be played in the frame buffer before playing the image frame, and the storage space of the frame buffer is limited, for example, the frame buffer may be Only 10 frames can be saved. In addition, the low-efficiency bits in the high dynamic range image have a low correlation in space, and may not necessarily achieve good compression performance, so the conventional technology does not compress the inefficient bit images formed by the low-efficiency bits. .

In this way, in response to the high number of pixels in high dynamic range images, it is necessary to increase the storage space of the picture buffer, resulting in an increase in production costs.

Therefore, it is necessary to improve the conventional technology.

Therefore, the main purpose of the present invention is to provide an image compression circuit and method that can effectively compress inefficient bit images to improve the disadvantages of the conventional technology.

An embodiment of the present invention discloses an image compression circuit, which is used in an image playback system to compress an inefficient bit image of an image before playing the image. The image compression circuit includes an inefficient bit processing unit , Used to receive the image and generate the low-efficiency bit image, wherein each pixel in the image includes multiple bits, and the low-efficiency bit image is at least one bit of the least efficient among the multiple bits A formed image; a separator, coupled to the inefficient bit processing unit, for separating the inefficient bit image into a plurality of single bit depth blocks, wherein the plurality of single bit depth blocks Has a bit depth of 1; and a code selection unit, coupled to the separator, is used to perform distortion-free compression coding on a first single bit depth block among the multiple single bit depth blocks to generate A first encoded block, and according to a compression rate corresponding to the first encoded block, decide whether to store the first encoded block in a buffer of the video playback system.

An embodiment of the present invention further discloses an image compression method for compressing an inefficient bit image of an image before playing the image. The image compression method includes receiving the image and generating the inefficient bit image, wherein Each pixel in the image includes multiple bits, and the low-efficiency bit image is an image formed by at least one bit of the least efficient of the multiple bits; the low-efficiency bit image is separated into a plurality of single bits A bit depth block, wherein the bit depth of the plurality of single bit depth blocks is 1; the first single bit depth block among the plurality of single bit depth blocks is subjected to distortion-free compression coding to Generating a first encoded block; based on the first single bit depth block and the first encoded block, obtaining a compression rate corresponding to the first single bit depth block; and based on the compression Rate determines whether the first encoded block is stored in a buffer of the video playback system.

Please refer to FIG. 1, which is a schematic diagram of an image playback system 1 according to an embodiment of the present invention. The video playback system 1 can be installed in a digital TV or digital TV set-top box, which includes an image compression circuit 10 and a buffer BF. Generally, the video playback system 1 stores the video frames to be played in the buffer BF before playing the video frames. For example, the buffer BF can temporarily store 10 video frames, and the video playback system 1 can play 30 video frames in 1 second. However, due to the limited storage space of the buffer BF, in order to make more effective use of the storage space of the buffer BF, the image compression circuit 10 can first perform inefficient bit image in the image frame before the image playback system 1 plays the image frame With compression, the image playback system 1 can store the compressed inefficient bit image in the buffer BF.

The image compression circuit 10 includes an inefficient bit processing unit 12, a splitter 14 and an encoding selection unit 16. The inefficient bit processing unit 12 receives an image I, and generates an inefficient bit image I _{LSB of the} image I. Generally speaking, the image frame includes multi-monochromatic images corresponding to multiple dimensions in the color space. The multiple dimensions in the color space may be RGB (Red/Greed/Blue) or Y/Cb/Cr, where Y represents brightness ( Luminance), Cb, Cr stands for (Chrominance), where Cb stands for blue color difference, and Cr stands for red color difference. The image I may be a monochromatic image corresponding to the luminance Y (or blue color difference Cb) (or red color difference Cr) in the image frame. In addition, each pixel in the image I can be represented by K bits, and the low-efficiency bit image I _LSB is an image formed by the most/lower-efficiency N bits of the K bits. In other words, the inefficient bit processing unit 12 can discard (Most/More Significant) (KN) the most/more efficient (KN) bits out of the K bits of each pixel, while remaining (in image I) The least/lower-effect (Least/Less Significant) N bits of the K-bits of each pixel, the low-efficiency bit-image I _LSB is formed at the N bits of each pixel. Among them, (KN) can be 8, K can be 10 or 12, N can be 2 or 4. In addition, the bit depth (Bit Depth) of the inefficient bit image I _LSB is N.

The separator 14 is coupled to the inefficient bit processing unit 12 and is used to separate the inefficient bit image I _LSB into a plurality of single bit depth blocks UCB, wherein the bit depth of each single bit depth block UCB Is 1, that is, each pixel in each single-bit depth block UCB is only represented by a single bit. In an embodiment, the separator 14 may first separate the inefficient bit image I _LSB into a single bit depth image (ie, bit plane) UI ₁ ˜UI _N corresponding to the N least significant bits, respectively. , And then separate/divide the single-bit depth image UI _n (n=1,...,N) in space (Spatial, referring to the space formed by the image width (Width) and image height (Height)) into (belonging to single bit depth image UI _n) of a plurality of single-bit depth block UCB _n, while the single-bit depth image UI ₁ ~ UI _N plurality of single-bit depth block UCB ₁ ~ UCB _N is the separator 14 The generated multiple single-bit depth blocks UCB, that is to say, the separator 14 can first separate the inefficient bit image I _LSB in the bit depth dimension, and then perform the spatial separation/segmentation. In an embodiment, the separator 14 may first spatially separate/segment the inefficient bit image I _LSB into blocks CB ₍₁₎ to CB _(H) , and then divide the block CB _(h) (h=1 a plurality of single-bit depth block, ..., H) is separated into corresponding blocks CB _(h) of the UCB _(h), while the corresponding block _{CB (1) ~ CB (H} ) bit depth single block UCB ₍₁₎ ~ UCB _(H) are the multiple single-bit depth blocks UCB generated by the separator 14, in other words, the separator 14 can first spatially separate the inefficient bit image I _LSB / Segmentation, and then the separation in the bit depth dimension. In addition, a plurality of single bit depth blocks UCB can be output to the encoding selection unit 16 in chronological order.

The code selection unit 16 is coupled to the separator 14 and is used to perform distortionless compression coding on the single bit depth block UCB to generate a coded block CCB, and according to the compression performance corresponding to the coded block CCB (eg Compression ratio), selectively store the encoded block CCB in the buffer BF. In detail, please refer to FIG. 2, which is a schematic diagram of a code selection unit 26 according to an embodiment of the present invention. The code selection unit 26 may be used to implement the code selection unit 16, and the code selection unit 26 may include an encoder 260, a control unit 262, and a multiplexer MUX. The encoder 260 is used to perform lossless compression coding on the single-bit depth block UCB to generate a coded block CCB. The control unit 262 obtains the corresponding coded block according to the single-bit depth block UCB and the coded block CCB A compression rate R of the block CCB, and determine whether the compression rate R is less than a specific value γ. The compression ratio R can be R=IN(CCB)/IN(UCB), where IN(UCB) represents the data amount/bit number of a single bit depth block UCB, and IN(CCB) represents the data of the encoded block CCB Quantity/bit number. When the compression rate R is less than a specific value γ, the control unit 262 controls the encoding selection unit 26 to output the encoded block CCB, and the video playback system 1 stores the encoded block CCB in the buffer BF. Conversely, when the compression ratio R is not less than a specific value γ, the control unit 262 controls the encoding selection unit 26 to output a single bit depth block UCB, and the video playback system 1 stores the single bit depth block UCB in the buffer BF .

Furthermore, the control unit 262 can control the encoder 260 so that the encoder 260 can perform run-length encoding (Run-Length Encoding, respectively) on a single bit depth block UCB according to a plurality of different scanning sequences SS ₁ ˜SS _G , respectively. RLE) (Run-length encoding is a distortion-free compression encoding), and a plurality of pre-encoding blocks PCB ₁ to PCB _G corresponding to multiple scanning sequences SS ₁ to SS _G are generated, and the control unit 262 may calculate corresponding to the pre-encoding blocks The front compression ratio R ₁ ～R _{G of} PCB ₁ ～PCB _G. Similarly, the front compression ratio R _g (g=1,...,G) can be R _g =IN(PCB _g )/IN(UCB), IN( PCB _g ) represents the amount of data/bits of PCB _g in the previous coding block.

In an embodiment, the control unit 262 can control the encoder 260 so that the encoder 260 outputs the front coding blocks PCB ₁ to PCB _{g *} in the front coding blocks PCB ₁ ˜PCB _G (that is, the coding post-region output by the encoder 260 Block CCB), where the pre-compression rate R _g* corresponding to the pre-coding block PCB _{g *} is the minimum value of the pre-compression rate R ₁ ～R _G , that is, R _g* =min(R ₁ ,...,R _G ) , Where the front compression ratio R _{g* is} the minimum front compression ratio. In this way, the encoded block CCB output by the encoder 260 is the pre-encoding block PCB _{g *} , and the compression rate R of the encoded block CCB is the pre-compression rate R _g* .

In an embodiment, the control unit 262 can control the encoder 260 so that the encoder 260 performs run-length encoding on the subsequent single-bit depth block UCB according to the optimal scanning order SS _g* corresponding to the minimum compression rate R _{g *} , In other words, at time t0, the encoder 260 can separately run-length encode the single bit depth block UCB ⁰ received at time t0 according to the scanning order SS ₁ ˜SS _G , and at the same time, the control unit 262 can obtain the minimum compression rate R _{g *} and the optimal scanning order SS _g* . At time tn after time t0, the control unit 262 can control the encoder 260 so that the encoder 260 can scan multiple single-bit depth regions after the single-bit depth block UCB ⁰ according to the optimal scanning order SS _g* The block UCB ⁿ performs run- ^length coding.

In addition, the scanning sequence SS ₁ to SS _G may include horizontal line-by-line scanning (Raster Scan), vertical line-by-line scanning (Vertical Scan), spiral scanning (Circular Scan), line-by-line snake scanning (Raster Snake), vertical snake Scanning (Vertical Snake) or meandering (Zig-Zag) scanning and other different scanning order, as shown in Figure 3, is not limited to this.

When the control unit 262 determines that the compression ratio R is less than a specific value γ, the control unit 262 generates a selection signal sel to control the multiplexer MUX to output the encoded block CCB. Conversely, when the control unit 262 determines that the compression ratio R is not less than a specific value γ, the control unit 262 generates a selection signal sel to control the multiplexer MUX to output a single bit depth block UCB.

The operation of the image compression circuit 10/image playback system 1 can be further summarized as an image compression method. Please refer to FIG. 4, which is a flowchart of an image compression method 40 according to an embodiment of the present invention. The image compression method 40 may include the following steps:

Step 400: Receive the image I, and generate the inefficient bit image I _{LSB of the} image I.

Step 402: Separate the inefficient bit image I _LSB into multiple single-bit depth blocks UCB.

Step 404: Perform distortion-free compression coding on the single-bit depth block UCB to generate a coded block CCB.

Step 406: Obtain the compression rate R corresponding to the encoded block CCB according to the single bit depth block UCB and the encoded block CCB.

Step 408: Determine whether the compression ratio R is less than a specific value γ? If yes, go to step 410; if no, go to step 412

Step 410: Store the encoded block CCB in the buffer BF.

Step 412: Store the single bit depth block UCB in the buffer BF.

In the image compression method 40, step 400 may be performed by the inefficient bit processing unit 12, step 402 may be performed by the separator 14, step 404 may be performed by the encoding selection unit 16 or the encoder 260, and steps 406 and 408 may be performed by the encoding selection unit 16 or the control unit 262 to execute. For the remaining operation details of the image compression method 40, please refer to the aforementioned relevant paragraphs, which will not be repeated here.

In general, the most/more efficient (KN) bits in the image should have a higher spatial correlation, that is, the bit values of adjacent pixels have a higher correlation, which can achieve better compression performance. However, the most/lower-efficiency N bits in the image have a lower correlation and may not necessarily achieve good compression performance. Therefore, the conventional technology does not compress the low-efficiency bit image I _LSB .

In contrast, the present invention can compress the low-efficiency bit image I _LSB . To put it simply, the present invention separates the inefficient bit image I _LSB into a single bit depth image UI/bit plane, and after cutting the single bit depth image into a single bit depth block UCB, try Different scan sequences are used to run-length encode a single bit depth block UCB. If good compression performance can be achieved, the encoded block CCB is stored in the buffer BF. In addition, the present invention can run-length encode the subsequent single bit depth block according to the optimal scanning order.

The invention can be used to process high dynamic range (High Dynamic Range) images. In order to make the image have a high dynamic range, the current image standard expands the number of pixel bits from 8 bits to 10 bits (HDR-10) or 12 bits (HDR-12). Among them, the most efficient 8-bit image/pixel can be compressed using the existing technology, and the least efficient 2-bit or 4-bit can be compressed using the present invention to further effectively use the buffer BF storage space effect. The above are only the preferred embodiments of the present invention, and all changes and modifications made in accordance with the scope of the patent application of the present invention shall fall within the scope of the present invention.

1‧‧‧Image playback system 10‧‧‧Image compression circuit 12‧‧‧Inefficient bit processing unit 14‧‧‧ Separator 16, 26‧‧‧Encoding selection unit 260‧‧‧Encoder 262‧‧‧Control Unit 40‧‧‧Method 400～412‧‧‧Step BF‧‧‧Buffered CCB‧‧‧Coded block I, I _LSB ‧‧‧ Video MUX‧‧‧Multiplexer UCB‧‧‧ Single bit depth Block

FIG. 1 is a block diagram of an image playback system according to an embodiment of the invention. FIG. 2 is a block diagram of a code selection unit according to an embodiment of the invention. FIG. 3 is a schematic diagram of multiple scanning sequences according to an embodiment of the invention. FIG. 4 is a flowchart of an image compression method according to an embodiment of the invention.

1‧‧‧Video playback system

10‧‧‧Image compression circuit

12‧‧‧Inefficient bit processing unit

14‧‧‧separator

16‧‧‧Code selection unit

I, I _LSB ‧‧‧ video

BF‧‧‧Buffer

UCB‧‧‧Single bit depth block

Claims (19)

An image compression circuit is used in an image playback system to compress an inefficient bit image of an image before playing the image. The image compression circuit includes: an inefficient bit processing unit for receiving The image, and the inefficient bit image is generated, wherein each pixel in the image includes a plurality of bits, and the inefficient bit image is an image formed by at least one bit of the least efficient of the plurality of bits A separator, coupled to the inefficient bit processing unit, used to separate the inefficient bit image into multiple single bit depth blocks, wherein the bit depth of the multiple single bit depth blocks Is 1; and a code selection unit, coupled to the separator, is used to perform distortionless compression coding on a first single bit depth block among the plurality of single bit depth blocks to generate a first code After the block, and according to a compression rate corresponding to the first encoded block, it is determined whether to store the first encoded block in a buffer of the video playback system. The image compression circuit according to claim 1, wherein the encoding selection unit comprises: an encoder for performing distortion-free compression encoding on the first single bit depth block to generate the first encoded post-region Block; and a control unit for obtaining the compression rate corresponding to the first encoded block based on the first single bit depth block and the first encoded block, and determining the compression rate according to the compression rate Whether to store the first encoded block in the buffer. The image compression circuit according to claim 1, wherein when the compression ratio is less than a specific value, the control unit controls the code selection unit to output the first coded block, and the image playback system divides the first coded area The block is stored in the buffer. The image compression circuit according to claim 3, wherein when the compression ratio is not less than the specific value, the control unit controls the code selection unit to output the first single bit depth block, and the image playback system applies the first A single bit depth block is stored in the buffer. The image compression circuit according to claim 1, wherein the separator separates the inefficient bit image into at least one single bit depth image, and separates the at least one single bit depth image into the plurality of single bits Deep blocks. The image compression circuit of claim 1, wherein the separator separates the inefficient bit image into a plurality of blocks, and separates the plurality of blocks into the plurality of single bit depth blocks. The image compression circuit according to claim 1, wherein the control unit controls the encoder so that the encoder performs run-length encoding on the first single bit depth block according to a plurality of scanning sequences, respectively RLE), a plurality of pre-encoded blocks corresponding to the plurality of scan sequences are generated, and the first post-encoded block is related to the pre-encoded block having the smallest compression rate among the plurality of pre-encoded blocks. The image compression circuit according to claim 7, wherein the plurality of scanning sequences include horizontal line-by-line scanning (Raster Scan), vertical line-by-line scanning (Vertical Scan), spiral scanning (Circular Scan), and line-by-line serpentine scanning ( Raster Snake, Vertical Snake or Zig-Zag scanning. The image compression circuit according to claim 7, wherein the plurality of pre-encoding blocks respectively have a plurality of pre-compression ratios, and the control unit obtains a minimum pre-compression ratio among the multiple pre-compression ratios, the minimum pre-compression ratio corresponding to In an optimal scanning order among the plurality of scanning orders, the control unit controls the encoder so that the encoder is in the first single bit in the plurality of single bit depth blocks according to the optimal scanning order A plurality of second single-bit depth blocks after the depth block are run-length encoded. The image compression circuit according to claim 1, wherein the encoding selection unit includes: a multiplexer controlled by the control unit; wherein, when the compression ratio is less than the specific value, the multiplexer outputs the first Block after encoding. The image compression circuit of claim 1, wherein when the compression ratio is not less than the specific value, the multiplexer outputs the first single bit depth block. An image compression method for compressing an inefficient bit image of an image before playing the image. The image compression method includes: receiving the image and generating the inefficient bit image, wherein each of the images The pixel includes a plurality of bits, and the inefficient bit image is an image formed by at least one of the least effective bits among the plurality of bits; the inefficient bit image is separated into a plurality of single bit depth blocks , Where the bit depth of the plurality of single bit depth blocks is 1; a distortion-free compression coding is performed on a first single bit depth block among the plurality of single bit depth blocks to generate a first code After the block; based on the first single bit depth block and the first encoded block, obtain a compression rate corresponding to the first single bit depth block; and based on the compression rate, decide whether to The first encoded block is stored in a buffer of the video playback system. The image compression method according to claim 12, further comprising: determining whether the compression rate is less than a specific value; and when the compression rate is less than the specific value, storing the first encoded block in a buffer. The image compression method according to claim 13, further comprising: when the compression ratio is not less than the specific value, storing the first single bit depth block in the buffer. The image compression method according to claim 12, wherein the step of separating the first monochromatic inefficient bit image into a plurality of single bit depth blocks includes: separating the inefficient bit image into at least one unit Bit depth image; and separating the at least one single bit depth image into the plurality of single bit depth blocks. The image compression method according to claim 12, wherein the step of separating the first monochromatic low-efficiency bit image into a plurality of single bit depth blocks includes: separating the low-efficiency bit image into a plurality of regions Block; and separating the plurality of blocks into the plurality of single bit depth blocks. The image compression method according to claim 12, wherein the step of performing distortion-free compression encoding on the first single bit depth block to generate the first encoded block includes: according to multiple scanning orders, respectively Run-Length Encoding (RLE) the first single bit depth block to generate multiple pre-encoded blocks corresponding to the multiple scan sequences; and generate the first post-encoded block, wherein the first The encoded block is related to the pre-encoded block having the smallest compression rate among the plurality of pre-encoded blocks. The image compression method according to claim 17, wherein the plurality of scanning sequences include horizontal line-by-line scanning (Raster Scan), vertical line-by-line scanning (Vertical Scan), spiral scanning (Circular Scan), and line-by-line snake scanning ( Raster Snake, Vertical Snake or Zig-Zag scanning. The image compression method according to claim 17, wherein the plurality of pre-encoded blocks each have a plurality of pre-compression ratios, and the image compression method further comprises: obtaining a minimum pre-compression ratio among the plurality of pre-compression ratios, wherein the The minimum pre-compression ratio corresponds to an optimal scanning order among the plurality of scanning orders; and according to the optimal scanning order, the multiple of the plurality of single bit depth blocks after the first single bit depth block A second single bit depth block is run-length encoded.

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