JPS63111768A - Image data quantizer - Google Patents

Abstract

PURPOSE:To realize efficient picture data compression regardless of a dynamic range of a picture signal by varying a quantized step dynamically in response to the varying state of data and designating the maximum and minimum steps optionally. CONSTITUTION:An input signal eliminated with a DC by a DC component eliminating device 41 is fed to an absolute difference calculator 42, where a difference alphaof an absolute value is calculated. On the other hand, when a dynamic range input device 43 gives a value beta to decide the dynamic range of the input signal, a step calculator 44 applies arithmetic operation to obtain a tentative value 2<n>. The step 2<n> is limited by a step range limiter 45 so that it comes between the maximum step Smax and the minimum step Smin inputted externally. In case of the relation of 2<n>>Smax and 2<nSmin, the step is decided respectively to be the Smax, Smin and the step values decided in this way are quantized by a quantization executing device 46.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image data quantization device for quantizing image data.

[Conventional technology]

Conventionally, when transmitting image data, it has been quantized and then transmitted, because if it is transmitted as is, there will be a lot of distortion.

[Problem that the invention seeks to solve]

However, in conventional devices, the step value for quantization is fixed, so in order to quantize an input signal with a wide dynamic range over the entire range, the number of steps must be increased. There is a problem in that it is not possible to quantize fine details for narrow input signals.

[Means for solving problems]

In order to solve such problems, the present invention provides a step value calculation device that determines a temporary step value, and a step value that determines the final step value from the relationship between the upper limit value, the lower limit value, and the temporary step value. A step value range limiting device is provided.

[Effect]

A temporary step value is determined from the difference in absolute values, and when this temporary step value is larger than the upper limit, the upper limit is used, and when it is within the range between the upper and lower limits, the temporary step value is used as the lower limit. In the following cases, the lower limit value is finally determined as the step value.

〔Example〕

FIG. 2 is a block diagram showing an example of an image transmitting device and an image receiving device to which the present invention is applied.

In the figure, input data 2 signal-converted by a two-dimensional discrete cosine transform device 1 has its low level portion cut off by a cutter 3, quantized by a quantizer 4, and encoded by an encoder 5. and sent to the transmission line 6. The transmitted signal is decoded by the decoding device 7, returned to the original signal by the inverse quantization device 8, and the values cut off at the transmitting side are added by the cutoff and value addition device 9, resulting in a two-dimensional discrete The signal is inversely transformed by a cosine inverse transformer 10, and an output signal 11 is taken out.

FIG. 1 is a block diagram showing an embodiment of a quantization device 4, which is a main part of the present invention. In the figure, the absolute value difference α of the input signal from which the DC component has been removed by the DC component removing device 41 is calculated by the absolute value difference calculating device 42 . on the other hand,
β is a value for suppressing the dynamic range of the input signal input from the dynamic range input device 43 to a certain value.
Then, the step value calculation device 44 performs the following calculation to obtain 2 as a temporary step value. Here, n takes the smallest value among non-negative integers.

The temporary step value 2 is limited in value by the step value range limiting device 45 as follows. The step value range limiting device 45 receives the maximum step value Smax from the outside,
A minimum step value Sm1n is provided. At this time, the maximum step value Sm! Ic is set to a large value when the maximum value of the image data is large, and is determined so as not to cause an error between the original image data and the quantized data. minimum step value S
□in is set to a small value when the change in the low level portion of the image data is large. Then, when the temporary step value 2n has the following relationship, the temporary step value 2n is determined as the step value S.

Sm1n≦2≦5nla! If this relationship does not hold, the step value S is set to Sm1n if 2<Smtn, and the step value S is set to SmaX if 2n>Sm. The quantization execution device 46 uses the step value S determined in this way.
Quantization is performed by

〔Effect of the invention〕

As explained above, the present invention is capable of dynamically changing the quantization step value according to the changing situation of data so as to fall within an arbitrarily specified dynamic range value, and of changing the minimum and maximum step values arbitrarily. By specifying the value, image data compression can be efficiently executed regardless of the dynamic range of the image signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram of an apparatus constructed to which the present invention is applied. 4...Quantization device, 41...-DC component removal device,
42... Absolute value difference calculation device, 43. Dynamic range input device, 44. 0. Step value calculation device, 45-... Step value range limiting device, 46.
...Quantization execution device.

Claims (2)

[Claims] (1) In an image data quantization device that quantizes image data using a predetermined step value, a step value calculation device that determines a temporary step value from the difference in absolute values, and a step value calculation device that determines a temporary step value, and this temporary step value is larger than the upper limit value. and a step value range limiting device that uses the upper limit value as the step value when the step value is within the range between the upper limit value and the lower limit value, and uses the lower limit value as the step value when it is below the lower limit value. Image data quantization device. (2) The image data quantization device according to claim 1, wherein the upper limit value and the lower limit value can be controlled from the outside.