CN1610377A - Method for compressing colour space conversion of 16 bit colour image - Google Patents

Abstract

The present invention discloses one kind of color space transformation method for compressing 16-bit color image. On the basis of traditional image or video compression technology, such as JPEG sequence, MPEG sequence and H.26X sequence, one conversion from 24-bit RGB format to 16-bit RGB format is increased to the encoding end, and the color space transformation method is used to eliminate the redundant information in the input end and simplify the operation steps in the decoding end, so as to reduce the decoding complexity and raise the video compression quality.

Description

Be used to compress the method for the color notation conversion space of 16 coloured images

Technical field

The present invention relates to the relevant multimedia technology field of portable mobile equipment, particularly relate to a kind of method that is used to compress the color notation conversion space of 16 coloured images.

Background technology

Along with popularizing of portable mobile equipment, personal digital assistant (PDA) for example, mobile phones etc. are based on the multimedia application emerge in multitude of portable mobile equipment.Portable mobile equipment exists that computing capability is weak, battery life short, LCD panel is 16 problems such as colour; And in the multimedia, the computation complexity of video decode is higher relatively, and therefore traditional video coding mode is used for portable mobile equipment, can't satisfy the user to the multimedia especially demand of video technique related application.At the portable equipment inherent characteristics, the generic video encoding and decoding technique is transformed, can improve the processing speed of video decode and the performance of video compression algorithm.

What is called is used for the color notation conversion space of compressed image, is meant the digital picture of input is carried out linear transformation, is mapped to the defined color space of corresponding compression algorithm.This color space is applicable to the compression of digital picture and video.The digital picture here comprises common digital picture and the frame in the digital video sequences.

Digital picture and video coding technique generally adopt YCrCb as the color space that is used to compress.When being input as the RGB image, this color space is divided into a luminance component Y and two chromatic component CrCb with the RGB colouring information.Because human eye much larger than colourity, therefore carries out sampling in 1: 1 in compression process to brightness to the sensitivity of brightness, and colourity is carried out sampling smaller or equal to 1: 1, thereby realize compression to a certain degree.At present, conventional compression techniques is the YCrCb form with 24 RGB image transforms.

As previously mentioned, the LCD panel of portable mobile equipment is not supported the image of 24 rgb formats, but supports 16 rgb format images, comprises two kinds of concrete forms of RGB565 and RGB555.Adopt traditional compress technique, display end must be transformed into 24 rgb formats earlier by YCrCb with decoded image, and then becomes 16 rgb formats that can show.Such method will inevitably increase operand, and the RGB24 form has comprised more colouring information than RGB16 form simultaneously, and these information are unnecessary on the display device of only supporting the RGB16 form.

If can define a color space mapping from RGB16 to YCrCb at the characteristics of RGB16 color space, then can improve compression efficiency, and reduce decoding complex degree.

Summary of the invention

The object of the present invention is to provide a kind of method that is used to compress the color notation conversion space of 16 coloured images.

The technical scheme that the present invention solves its technical problem employing is as follows:

1) when coding transforms to new color space with the coloured image of 16 rgb formats according to formula (1), called after rYCrCb, and the character of this color space is the same with YcrCb, and the RGB colouring information is divided into a luminance component Y _rWith two chromatic component Cr _r, Cb _r, can be used for compression; Follow-up compression process comprises sampling, dct transform, quantification, Run-Length Coding, variable-length encoding, can be on the gained transformation results, according to existing image or video compression standard, comprise JPEG series, MPEG series, H.26X serial, adopt its encryption algorithm step, get final product;

Y _r＝R+G+B

Cb _r＝4B-Y _r＝-R-G+3B (1)

Cr _r＝4R-Y _r＝3R-G-B

Wherein: R, G, B represent the R of picture element in 16 RGB images respectively, G, the numerical value of three components of B, Y _rRepresent luminance component in the rYCrCb space, Cb _r, Cr _rRepresent two chromatic components in the rYCrCb space respectively; Following formula (2) is that the matrix form of formula (1) is expressed;

$\left[\begin{array}{c}{Y}_r\\ {\mathrm{Cb}}_r\\ {\mathrm{Cr}}_r\end{array}\right]=\left[\begin{array}{ccc}1& 1& 1\\ -1& -1& 3\\ 3& -1& -1\end{array}\right]\·\left[\begin{array}{c}R\\ G\\ B\end{array}\right]---\left(2\right)$

Wherein: symbol is identical with formula (1);

When 2) decoding, according to existing image or video compression standard, comprise JPEG series, MPEG series, H.26X serial, adopt its encryption algorithm step to obtain data on the rYCrCb space, obtain the data of 16 rgb formats according to the inverse transform method of formula (3), directly output to portable equipment and show;

G＝(2Y _r-Cb _r-Cr _r)//4

R＝(Y _r+Cr _r)//4 (3)

B＝(Y _r+Cb _r)//4

Wherein: letter character is identical with formula (1), and " // " expression rounds up.

The present invention compares with background technology, and the useful effect that has is:

The present invention is a kind of method of brand-new color notation conversion space.It is applicable to the compression of 16 RGB coloured images or video.On traditional image or video compression technology basis, for example JPEG series, MPEG series, series H.26X, coding side increases the conversion of 24 rgb format to 16 rgb formats, and adopt this color notation conversion space method, can remove the unnecessary information of input and simplify the operating procedure of decoding end, thereby can reduce decoding complex degree, improve the video compression quality.

Embodiment

When implementing digital picture or video compression, all algorithms must carry out on a certain specific color space.For example, compression standard in current extensive employing, JPEG series, MPEG series, H.26X serial, when the form of digital picture of importing or video is RGB24, then use the transformation for mula of recommending, transform to the YCrCb space, sample then, compression steps such as dct transform, quantification, Run-Length Coding and variable-length encoding; When if form is RGB16, then the RGB24 form is arrived in the RGB16 format conversion by cover, carry out the aforesaid operations step then.Otherwise decode procedure then, finally can obtain the image or the video of RGB24 form; Show the RGB16 form if desired, then the RGB16 form is arrived in the RGB24 format conversion by cut position.In this process, compression stroke is the YCrCb space.

On portable mobile equipment, if at the image or the video compression of RGB16 form, adopt the compression stroke rYCrCb space of the present invention's design, only need color notation conversion space module in the said process replaced and get final product.Concrete steps are as follows:

During coding, when the form of digital picture of importing or video is RGB16, use formula (1), the rYCrCb space is arrived in data conversion; If form is RGB24, then the RGB16 form is arrived in the RGB24 format conversion by cut position, re-use formula (1).On compression stroke rYCrCb, can adopt compression steps such as traditional sampling, dct transform, quantification, Run-Length Coding and variable-length encoding to compress.This step can be eliminated unnecessary information, can improve compression efficiency.

During decoding, at first carry out traditional decompression step, obtain the data in rYCrCb space.At this moment, use formula (3), can obtain the image or the video of RGB16 form, directly output to the display device of supporting the RGB16 form.Therefore, the decoding complex degree of this method is low, and efficient is then higher.

Claims (1)

1. method that is used to compress the color notation conversion space of 16 coloured images is characterized in that:

1) when coding transforms to new color space with the coloured image of 16 rgb formats according to formula (1), called after rYCrCb, and the character of this color space is the same with YcrCb, and the RGB colouring information is divided into a luminance component Y _rWith two chromatic component Cr _r, Cb _r, can be used for compression; Follow-up compression process comprises sampling, dct transform, quantification, Run-Length Coding, variable-length encoding, can be on the gained transformation results, according to existing image or video compression standard, comprise JPEG series, MPEG series, H.26X serial, adopt its encryption algorithm step, get final product;

Y _r＝R+G+B

Cb _r＝4B-Y _r＝-R-G+3B (1)

Cr _r＝4R-Y _r＝3R-G-B

Wherein: R, G, B represent the R of picture element in 16 RGB images respectively, G, the numerical value of three components of B, Y _rRepresent luminance component in the rYCrCb space, Cb _r, Cr _rRepresent two chromatic components in the rYCrCb space respectively; Following formula (2) is that the matrix form of formula (1) is expressed;

$\left[\begin{array}{c}{Y}_r\\ {\mathrm{Cb}}_r\\ {\mathrm{Cr}}_r\end{array}\right]=\left[\begin{array}{ccc}1& 1& 1\\ -1& -1& 3\\ 3& -1& -1\end{array}\right]\·\left[\begin{array}{c}R\\ G\\ B\end{array}\right]---\left(2\right)$

Wherein: symbol is identical with formula (1);

When 2) decoding, according to existing image or video compression standard, comprise JPEG series, MPEG series, H.26X serial, adopt its encryption algorithm step to obtain data on the rYCrCb space, obtain the data of 16 rgb formats according to the inverse transform method of formula (3), directly output to portable equipment and show;

G＝(2Y _r-Cb _r-Cr _r)//4

R＝(Y _r+Cr _r)//4 (3)

B＝(Y _r+Cb _r)//4

Wherein: letter character is identical with formula (1), and " // " expression rounds up.