JPH0364192A - Picture signal processor - Google Patents

Abstract

PURPOSE:To correct only a contrast without changing attributes of colors except the brightness by applying gamma correction only to a brightness signal according to an accumulated brightness distribution curve and reconverting a three- primary color output picture signals with the brightness signal subjected to gamma correction and two kinds of color difference signals. CONSTITUTION:A signal separator means 1 which separates an R.G.B three- primary color input picture signal into a brightness signal Y and two kinds of color difference signals I, Q, and a histogram preparing means 2 prepares a histogram from the Y signal and an accumulated brightness distribution curve setting means 3 prepares an accumulated brightness distribution curve from the histogram. Then a gamma correction table value generated from the curve is set to a Y signal gamma correction means 4 and the Y signal gamma correction means 4 applies gamma correction to the Y signal only and a signal conversion means 5 converts the Y signal subjected to gamma correction and I and Q signals not subjected to gamma correction into the R.G.B three-primary color output picture signal. Thus, only the contrast is corrected and other color attributes are preserved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image processing device that improves and corrects the contrast of an input image signal to obtain an image having desired gradation characteristics.

[Prior Art] FIG. 3 is a functional block diagram of a device for determining brightness distribution and cumulative brightness distribution in a conventional image signal processing device disclosed in, for example, Japanese Patent Application Laid-Open No. 60-84084. (11) is a histogram creation means for creating a histogram of brightness levels from the R2O and B33 original input image signals, and (12) is a cumulative brightness distribution curve setting means for setting the accumulation of the histograms created by the histogram creation means (11). , (13) is the R signal gamma correction means, (1
4) is a G signal gamma correction means, and (15) is a B signal gamma correction means.
5) performs gamma correction using the cumulative brightness distribution curve from the cumulative brightness distribution curve setting means (12).

FIG. 4 is a diagram showing a histogram of the luminance level of the input image signal and its cumulative curve. In this case, the luminance level U on the horizontal axis is digitized to 0 to 255, and the frequency V on the vertical axis is also normalized to 0 to 255. Moreover, the cumulative frequency is shown as a percentage. As is clear from this figure, the cumulative curve is steep in areas where the occurrence frequency is high, and is gentle in areas where the frequency is low.

Next, the operation will be explained. The R, G, and B33 original input image signals are digital data and take values from 0 to 255.

These color data indicate white in R-G-B-255, and the larger the value, the brighter it is.

If the brightness of the input image signal is Y, for example, Y-0,3O
It can be determined using the relational expression R+0.59G+0.11B, which again results in a value between 0 and 255.

Using this relational expression, the distribution of brightness levels over the entire frame of the image to be recorded is determined by the solid line (6
) is obtained. When the above-mentioned histogram is cumulatively calculated for this image data, a cumulative distribution curve shown by the broken line (7) in the figure is obtained.

The horizontal axis U of this cumulative brightness distribution curve is the input brightness level from 0 to
255, and if the value of the vertical axis V is also normalized to 0 to 255, a relational expression representing this curve can be obtained. If this function is V-F (U), the frequency V can be obtained as a gamma-converted value of the input luminance level U.

Actually, it is sufficient to have this function as a table and find the output luminance level by referring to the table. In the table conversion, gamma correction is performed for each of the R, G, and B33 originals shown in FIG. 3 using the same cumulative brightness distribution curve.

[Problem to be Solved by the Invention] Since the device for calculating the brightness distribution and cumulative brightness distribution in the conventional image signal processing device is configured as described above, it is necessary to use the same gamma correction for each of the R, G, and B33 originals. Since a cumulative brightness distribution curve is used, there is a problem that when used for contrast enhancement, attributes such as hue in addition to brightness change.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an image signal processing device that can perform contrast correction without changing hue attributes other than brightness.

[Means for Solving the Problems] An image signal processing device according to the present invention includes a signal separation unit that separates an input image signal of three primary colors into a luminance signal and two types of color difference signals, and creates a histogram of the luminance levels. a histogram creation means, a cumulative brightness distribution curve setting means for setting a cumulative brightness distribution curve that is the accumulation of the histograms, and a gamma correction means for gamma-correcting the brightness signal input from the signal separation means using the cumulative brightness distribution curve; The gamma-corrected luminance signal and the two types of color difference signals are
and a signal converting means for converting into primary color output image signals.

[Operation] The image signal device according to the present invention converts input image signals of three primary colors into a luminance signal and two types of color difference signals, and performs gamma correction on only the luminance signal using a cumulative luminance distribution curve that is an accumulation of luminance level histograms. However, by reconverting the three primary color output image signals from this gamma-corrected luminance signal and the two types of color difference signals, only the contrast is corrected without changing color attributes other than luminance.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
In the figure, (1) is a signal separation means that separates the input image signal of R, G, and B33 originals into a luminance signal (Y) and two types of color difference signals (1, Q), and (2) is a histogram of luminance levels. (3) is a cumulative brightness distribution curve means for setting a cumulative brightness distribution curve that is a cumulative histogram; (4) is a gamma correction means for gamma-correcting a brightness signal using the cumulative brightness distribution curve; 5) is a gamma-corrected luminance signal (Y) and two types of color difference signals (1, Q)
This is a signal converting means for converting the image signal from the R, G, B33 original image signal.

Next, the operation of the above embodiment will be explained with reference to the flowchart shown in FIG. Here, the input image signal for which contrast correction is to be performed is already stored in the image memory, for example.
It is assumed that the same input image signal can be transferred twice to the image signal processing device configured in the above embodiment.

First, R, G, B33 original input image signals are converted into Y, I, Q signals by the signal separation means (1) (Step 5T-1
). Of these, the histogram creation means (
2) Create a histogram (step 5T2-2)
.

Then, the cumulative brightness distribution curve setting means (3) creates a cumulative brightness distribution curve from the above-mentioned histogram (step 5T).
-3). At this time, the cumulative brightness distribution curve itself may be used as the gamma correction table, or it may be used in a modified form. The gamma correction table values created in this manner are set in the Y signal gamma correction means (4) (step 5T-4).

The above operations are the gamma correction table creation process and correspond to the first transfer of the input image signal to the image signal processing device.

After the gamma correction table value is set in the Y signal gamma correction means (4), the second input image signal is transferred and contrast correction is performed.

First, the input image signals of R, G, and B33 originals are converted into Y, I, and Q signals by the signal separation means (19) (step 5T-
5). Of these, only the Y signal is subjected to gamma correction by the Y signal gamma correction means (4) (step 5T-6).

Then, the signal conversion means (5) converts the gamma-corrected Y signal and uncorrected I and Q signals into R, G, and B33 original output image signals (step 5T-7).

In this way, since gamma correction is performed only on the Y signal, color attributes other than brightness (or brightness) can be preserved.

In the above embodiment, R, G, and B33 original input image signals are illustrated, but other three input image signals such as Y (yellow, different from the above luminance signal), M (magenta), and C (cyan) are also used. Primary color input image signals may also be used. In the above embodiment, a set of I and Q is used as the two types of color difference signals, but other color difference signals may be used.

Further, in the above embodiment, the luminance signal and two types of color difference signals are converted into the output image signal of R, G, and B33 originals, which are the same as the input image signal, but these do not necessarily have to be the same. For example, the input image signal may be a signal of R, G, and B33 primary colors, and the output image signal may be a signal of Y, M, and C3 primary colors.

Additionally, when creating a histogram of brightness levels,
In the above embodiment, pixels of the entire input image signal are used, but in order to reduce processing time, a histogram may be created from the luminance level of a part of the input image signal by sampling.

[Effects of the Invention] As described above, according to the present invention, an input image signal of three primary colors is separated into a luminance signal and two types of color difference signals, and gamma correction is performed only on the luminance signal. 3 from a luminance signal and two types of color difference signals without gamma correction.
Since the configuration is configured to obtain output image signals of primary colors, there is an effect that only the contrast can be corrected while other color attributes can be maintained.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram showing an image signal processing device according to an embodiment of the present invention, FIG. 2 is a flow chart explaining the operation of FIG. 1, and FIG. 3 is a luminance distribution and accumulation in a conventional image signal device. FIG. 4, which is a functional block diagram of the apparatus for determining the brightness distribution, is a diagram showing the histogram of the brightness level of the input image signal and its cumulative curve. In the figure, (1) is a signal separation means, (2) is a histogram creation means, (3) is a cumulative brightness distribution curve setting means, (
4) is a Y signal gamma correction means, and (5) is a signal separation means. In addition, in the figures, the same reference numerals indicate the same parts or the entrance port parts.

Claims (1)

[Scope of Claims] Signal separation means for separating input image signals of three primary colors into a luminance signal and two types of color difference signals; histogram creation means for creating a histogram of the luminance levels; and cumulative luminance that is the accumulation of the histograms. cumulative luminance distribution curve setting means for setting a distribution curve; gamma correction means for gamma-correcting the luminance signal input from the signal separation means using the cumulative luminance distribution curve; and gamma-corrected luminance signal and the two types of color difference signals. An image signal processing device comprising a signal converting means for converting a signal into an output image signal of three primary colors.