JP2752358B2 - Image signal processing method - Google Patents

Abstract

PURPOSE:To obtain a more precise image of input density scale proportional to the density scale of a regenerated image by applying a linear primary conversion of data so that it may become data applicable to the maximum/minimum density range of printer functions stored in a lookup table and converting data in a frame memory based on a new desired function. CONSTITUTION:A video signal from a display device 22 is disintegrated into color signals red, green and blue, and these signals are held by a sample hold circuit 24. Then the signals are converted to digital data by an A/D converter 26 and once is stored in a frame memory 28. Image data is transformed by means of a control circuit 30 including a direct memory access controller IC, and the converted data is introduced into a latch circuit 34 through a lookup table LUT 32 which generates a digital signal for driving three LED's relative to printer function Dp. Then after conversion by the D/A converter 36, three LED's LC, LM and LY light by a diode drive current from a driver 38, emitting lights of different wavelengths to a photosensitive material F. Thus a regenerated image is obtained after development.

Description

The present invention relates to a method of processing an image signal, and more particularly, to a method of processing an image signal.
A video signal is input from a video device such as an imaging device, the input video signal is converted into exposure data for image reproduction using a lookup table based on the input video signal, and a color hard copy is formed based on the converted exposure data. The present invention relates to a method of processing an image signal applied to an image output device for outputting. BACKGROUND OF THE INVENTION In recent years, a so-called image output device that creates a color hard copy based on a video signal output from a display device such as a CRT or an imaging device such as a camera has been used. FIG. 1 shows an example of this type of conventional image output apparatus. That is, the image output device includes a look-up table 8 that converts image data from the video device 2 into exposure data for driving, for example, light-emitting diodes LC, LM, and LY of three colors. The video signal output from the video device 2 is
The image data input to the frame memory 6 via the A / D converter 4 and stored in the frame memory 6 is converted into drive data for driving the light emitting diodes LC, LM and LY via the look-up table 8. The driving data is D / A
The current is converted into an actual drive current by the driver 12 via the converter 10 and supplied to the light emitting diodes LC, LM and LY.
Light emitted from the light emitting diodes LC, LM, and LY exposes the photosensitive material F, and the exposed photosensitive material F becomes a color hard copy through a developing process (not shown). Note that the function of the image output data _yi related to the image density / drive current conversion stored in the lookup table 8 is a printer function.
_Let D _p = P (y _i ). Incidentally, the image density / drive current conversion data stored in the look-up table 8 is the light emitting diode L
C, LM, and LY and data in a predetermined range determined from the characteristics of the photosensitive material F. Therefore, it is desirable that the density of the image data input to the look-up table 8 be image data having a density within the predetermined range. However, the density data output from the video device 2 is based on the minimum value D _pmin and the maximum value D _{pmax of the} printer function.
It is not uncommon for image data in a wider range to be output. When image data in a wider range is introduced into the frame memory 6, the density of the printer function D _p stored in the lookup table 8 is reduced. Since the input image data exceeding the range is converted, for example, so that the upper and lower limits are compressed, there is a disadvantage that the density gradation of the reproduced image is significantly impaired. [Object of the Invention] The present invention has been made to overcome the above-described disadvantages. A video signal is input from a video device such as an imaging device, and a look-up table is used based on the input video signal. when converting to the exposure data for exposure devices, the target function of the image density D _s of the image data {the image input data x _i to be input to the look-up table function D _s = T
A new target function _DNS is created by performing a linear first-order transformation so that｝ (x _i ) becomes data in the minimum / maximum density range of the printer function D _p stored in the lookup table. Then, by performing a conversion process on the data in the frame memory based on the new target function _DNS , it is possible to always perform exposure within the linear exposure range for the exposure elements LC, LM, and LY. It is an object of the present invention to provide a method of processing an image signal which enables a more precise image in which the density gradation is proportional to the input density gradation. [Means for Achieving the Object] In order to achieve the above object, the present invention provides a tone expression density function D _s (hereinafter, referred to as an original image data input to an image output device such as a printer having a finite tone expression range). , D _{s is referred} to as a target function) in a range exceeding a density range of a tone expression density function D _p (hereinafter, D _{p is referred} to as a printer function) relating to an image reproduced by the image output device. A processing method of an image signal to be used, wherein x _i (i is a finite integer)
The objective function D _s as an original image input data is _{D s = T (x i)} , a printer function y _i as the image output data D _p is D _p =
If P (y _i ), α and β are real numbers, the maximum value of the new target function D _NS is equal to or less than the maximum value of the printer function D _p , and the minimum value of the new target function D _NS is the printer function D _P Is selected so as to be equal to or more than the minimum value of D _NS, and the new target function D _NS is set to D _NS = αT (x _i ) +
It is characterized in that it is set to be β. [Embodiment] Next, a preferred embodiment of an image signal processing method according to the present invention will be described in detail with reference to the accompanying drawings, in relation to an apparatus for performing the method. In FIG. 2, reference numeral 20 denotes an image output device incorporating an apparatus for implementing the method for processing an image signal according to the present invention. The image output device 20 is a device that creates a color hard copy based on a video signal output from a display device 22 such as a CRT, for example. Video signals output from the display device 22 such as a CRT are color signals R (red) of three primary colors,
After being separated into G (green) and B (blue) and output, sampled and held by a sample and hold circuit 24, analog data is converted to digital data by an A / D converter 26,
The digital data is temporarily stored in the frame memory 28. The image data stored in the frame memory 28 is subjected to an image signal conversion process according to the present invention by the operation of a control circuit 30 including a direct memory access controller (DMAC) IC, and the data stored in the frame memory 28 is converted. You. Output data look-up table for generating a digital signal for three-color LED driver according to the printer function D _p of the image conversion processing frame memory 28 (hereinafter, LUT hereinafter) is introduced into the latch circuit 34 via a 32. Latch circuit
The image data from 34 is converted from digital data to analog data via a D / A converter 36 and then introduced into a driver 38. The three light emitting diodes LC, LM and LY emit light by the diode driving current from the driver 38,
Light of different wavelengths is emitted to the photosensitive material F. In addition,
The light emitting diode LC irradiates the photosensitive material F with infrared light for coloring the cyan (C) dye, the light emitting diode LM irradiates red light for coloring the magenta (M) dye, and the light emitting diode LY emits yellow (Y Irradiate yellow light to develop the dye of (d). The photosensitive material F exposed by the irradiation light includes:
A development image (not shown) is performed to obtain a reproduced image. An apparatus for carrying out the method of the present invention is basically configured as described above. Next, the operation and effects of the apparatus will be described. The third figure a is a printer function D _p stored in LUT32 created in accordance with the characteristics of the three primary light emitting diodes LC, LM and LY and the photosensitive material F. That is, the printer function D _p converts the density data input to the range of acceptable concentration range D _pmin to D _pmax to the image output data y _min to y _max. In addition,
Different printer functions are stored in the LUT 32 for each of the three primary colors R, G, and B. Therefore, the image data is now transferred from the display device 22 to the frame memory 28 via the sample and hold circuit 24 and the A / D converter 26.
Let's say it was introduced to In this case, the image data stored in the frame memory 28 is, for example, dot-sequential data divided into R, G, and B colors for each pixel. Therefore,
The density function of the introduced image data, that is, the target function
It is assumed that D _s = T (x _i ) has the distribution of FIG. 3B with respect to the image input data x _i . That is, the image input data
For x _i , the density D _s is the minimum / maximum value of the printer function D _p
Concentration data D beyond the range compared to D _pmin and D _pmax
smin and D _smax values. In this case, the image data x _i input, for example, the concentration D _1, D ₂ of the x _i1, x _i2 is the concentration outside the printer function D _p, in this case, the concentration of that range Is an image in which the gradation expression is remarkably deteriorated. Therefore, in order to eliminate the deterioration of the gradation expression, the direct memory access controller (DMA
The step of converting the image data in the frame memory 28 by the density conversion step according to C) will be described. In this case, the new objective function D _NS, as shown in FIG. 4 a, may be a function of the representation of _{D NS = αT (x) +} β. That is, the new target function D _NS is smaller than the old target function D _s by the offset β and the minimum / maximum value of the printer function D _p.
It is determined by the gradient α relating to D _pmin and D _pmax . The image data stored in the frame memory 28 is converted based on this equation. FIG. 4b shows the printer function D _{p of} FIG. 3a.
Is re-posted to explain. Figure 4 a, by referring to b, in the image input data x _i, the former objective function D _s range it was impossible for converting the printer function D _p of the image input data x _i1, x _i2 Etc. is the image output data y
_It will be appreciated that it can be converted to _i1 , _yi2 . In addition,
The selection of the offset β and the gradient α is, for example, that β is D
Select the corresponding value of _pmin , α is D _pmin ≤ D _NSmin , D _pmin ≥ D
_What is _necessary is _just to select in the range which simultaneously satisfies _Nsmax . By the image data subjected to the conversion process by the new target function _{DNS, the} output image data is a function having the widest density gradation,
That is, an image can be reproduced by using all the maximum density ranges of the characteristics of the printer function defined from the characteristics of the light emitting diodes LC, LM and LY and the photosensitive material F. [Effects of the Invention] As described above, according to the present invention, a target function relating to input image data is created in accordance with a printer function. For this reason, the range of input image data, that is,
Even when the density range of the original image data is wider than the reproduction range of the printer function, by modifying the target function, it is possible to smoothly reproduce the entire density range of the input image. As described above, the present invention has been described with reference to the preferred embodiment. However, the present invention is not limited to this embodiment.For example, it is possible to perform a first-order linear transformation without changing a printer function in its image output data range. Needless to say, various improvements and design changes can be made without departing from the gist of the present invention, for example, the lookup table may be changed to match the target function.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic block diagram of an image output device according to the prior art, and FIG. 2 is a schematic block diagram of an image output device incorporating a device for performing an image signal processing method according to the present invention. FIG. 3A is a characteristic diagram related to the printer function, FIG. 3B is a characteristic diagram related to the target function before the change, and FIG. 4A is a new diagram after the image signal processing method according to the present invention is performed. FIG. 4B is a characteristic diagram of the printer function again shown for comparison with FIG. 4A. 20 ... Image output device, 22 ... Display device 24 ... Sample hold circuit 26 ... A / D converter, 28 ... Frame memory 32 ... LUT, 34 ... Latch circuit 36 ... D / A converter , D _p … Printer function D _NS … New target function, D _s … Target function F… Photosensitive material LC, LM, LY… Light emitting diode

Claims (1)

(57) [Claims] Density value D _S of gradation function for image input data x _i (referred objective _{function) D S = T (x i} ) is, image output data y _i
A method of processing an image signal used when exceeding the concentration range of gradation function (printer _{function) D P = P (y i} ) ( minimum value D _Pmin ~ maximum D _Pmax) with respect to the new objective function D _NS = D _NS = αT (x _i ) + β (α and β are real numbers)
Set, the alpha, the value of beta, the minimum value D _NSmin concentration range of the new objective function D _NS becomes the minimum value D _Pmin or more values in the concentration range of the printer function D _P, and the new target Function D _NS
Method of processing an image signal, characterized in that the maximum value D _NSmax concentration range of is chosen to be a value within the maximum value D _Pmax in the concentration range of the printer function D _P.