KR20030019797A - Rgb format converter for image processing - Google Patents

Abstract

PURPOSE: An RGB conversion circuit in a color image processing system is provided to convert YCbCr into RGB with only serial connection of adders without having bit extension and multipliers. CONSTITUTION: An RGB conversion circuit in a color image processing system, which converts YCbCr format into RGB format includes 2M sign bit extension units, 3M adders(100), and M NOT-gates(200). The 2M sign bit extension units shift bit values of YCbCr component to the right n times and extend sign bits. The 3M adders are connected to the sign bit extension units and approximate the bit values, shifted to the right n times, to an added value of the bit values. The M NOT-gates are connected to the 3M adders.

Description

R.G./N. Conversion circuit in color image processing system {RGB FORMAT CONVERTER FOR IMAGE PROCESSING}

The present invention relates to an RGB conversion circuit, and more particularly, to an RGB conversion circuit in a color image processing system suitable for real-time conversion of the YCbCr format, which is a standard format for color image processing, to an RGB format, which is another standard format.

A typical YCbCr-RGB converter is implemented through a combination of multipliers and adders by approximating the coefficients in their transformation matrix.

However, in such an implementation method, a multiplier must be provided and a floating point arithmetic process is required, which increases computation time and software development time.

The present invention has been made to solve the above-described problems, color image processing system to implement the YCbCr-RGB conversion only by the serial connection of the adder without cross linking, bit expansion, multiplier of each bit using the characteristics of the binary system Its purpose is to provide an RGB conversion circuit in.

In order to achieve the above object, the present invention provides an RGB conversion circuit in a color image processing system that converts a YCbCr format into an RGB format, wherein 2M code bits shift the bit value of the YCbCr component to the right by n times and sign-bit extend. Expansion means; 3M adders connected to the sign bit expansion means and approximating the bit values shifted to the right n times by mutual addition values; An RGB conversion circuit in a color image processing system comprising M NOT-gates connected to 3M adders is provided.

1 is an RGB conversion circuit diagram according to a preferred embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

100: adder

200: NOT gate

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

First, the present invention approximates the multiplication between the coefficients and the variables in the YCbCr-RGB transformation matrix by mutual addition between shifting the multiplication value between 1.0 and the variable to the right n times. It will be easy to achieve what is meant by.

1 is a RGB conversion circuit according to an embodiment of the present invention, YCbCr format (Cb, Cr, Y), the sign bit expander (w _3, w _4, w _1, w _7), 6 adders 100, It consists of two NOT gates 200 and RGB formats (R, G, B).

When the hardware structure of FIG. 1 is expressed in the form of a transformation matrix, Equation 1 is obtained.

R = 1.0Y + 0.0Cb + 1.0Cr

G = 1.0 Y-(w ₃ + w ₄ ) Cb-(w ₁ + w ₇ ) Cr

B = 1.0 Y + 1.0 Cb

Hereinafter, a process of implementing the conversion matrix representing the RGB conversion circuit according to the present invention as shown in Equation 1 will be described in more detail.

First, a general YCbCr-RGB conversion matrix may be expressed as Equation 2 below.

R = 1.0 Y + 0.0 Cb + 1.0 Cr

G = 1.0 Y-0.1864 Cb-0.5085 Cr

B = 1.0 Y + 1.0 Cb

Equation 2 is approximated by mutual addition between 1.0 and a multiplication of the variable n times to the right.

For example, 0.5625 · Y can be regarded as the sum of the case where 1.0 · Y is shifted to the right once and the case of shifting to the right four times. At this time, the upper bits that become empty are implemented by sign bit extension filling the highest order bits. This can be expressed by the following equation (3).

0.5625 Y = 0.5 Y + 0.0625 Y

Here, looking at the case of shifting to the right once and the case of shifting to the right four times, it can be seen that the effect of multiplying the variable by 2 ⁻¹ every time the shift to the right one time is performed.

Accordingly, assuming that w _n is shifted to the right n times and code bit extended, w3 may be converted to the following equation (4).

_{0.5625 · Y = w 1 · Y} + w 4 · Y

In the present invention, since the 8-bit YCbCr format is targeted, the value of w _n when _{n has a} value from 1 to 7 is shown in Table 1 below.

w ₁ w ₂ w ₃ w ₄ w ₅ w ₆ w ₇ Counting value 0.5 0.25 0.125 0.0625 0.03125 0.015625 0.0078125

Accordingly, the YCbCr-RGB conversion equation shown in Equation 2 may be approximated to 0.1875, which is a sum of 0.125 and 0.0625 for 0.1864, and 0.5085 may be approximated to 0.5 and 0.0078125, and thus may be implemented as Equation 1 as described above. It can be.

Based on the technical idea described above, the YCbCr-RGB converter can be implemented by synthesizing the VHDL code.

As mentioned above, although this invention was concretely demonstrated based on the Example, this invention is not limited to this Example, Of course, various changes are possible within the range which does not deviate from the summary.

Therefore, the present invention can effectively implement the YCbCr-RGB conversion on the FPGA, and since the floating point operation is omitted, the operation time and software development time can be reduced.

Claims (2)

An RGB conversion circuit in a color image processing system for converting a YCbCr format into an RGB format, 2M sign bit expansion means for shifting the bit value of the YCbCr component n times (n is 1 to 7) to the right and sign bit expanding; 3M adders connected to the code bit expansion means and approximating the bit values shifted to the right n times by mutual addition values; RGB conversion circuit in a color image processing system comprising M NOT-gates connected to the 3M adders. The method of claim 1, The conversion matrix of the RGB conversion circuit is R = 1.0 Y + 0.0 Cb + 1.0 Cr G = 1.0 Y-(w ₃ + w ₄ ) Cb-(w ₁ + w ₇ ) Cr B = 1.0 Y + 1.0 Cb RGB conversion circuit in a color image processing system, characterized in that implemented by.