JPH07118818B2 - Still picture digital recorder - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital still image recording apparatus, and more specifically, to compressing image data representing a captured still image,
The present invention relates to a still image digital recording apparatus represented by a digital still camera that stores compressed data in a memory.

2. Description of the Related Art Conventional Problems and Their Problems Since large-capacity semiconductor digital memory chips can be mass-produced, digital still cameras, which digitize captured still images and store them in a memory, are in the limelight. It is preferable to compress the still image data in order to more effectively use the storage area of the memory and increase the number of recordable frames. A typical method for image data compression is W.CHEN and W.PRATT “Sce
ne Adaptive Coder "IEEE Trans.on Comm.Vol.COM-
32, No. 3, March 1984, pp 225-232. It divides the original image data into multiple blocks, orthogonally transforms the original image data for each block, obtains a transform coefficient, normalizes by dividing this transform coefficient by an appropriate normalization coefficient, and rounds the fraction. And quantize,
Compressed data is obtained by encoding this quantized value.

According to this method, the compression rate of image data can be arbitrarily set, that is, variable. If the compression rate is increased, the number of frames that can be recorded in the memory increases, but the quality of the recorded still image deteriorates. Conversely, if the compression rate is lowered, the number of frames that can be recorded in the memory will decrease, but the quality of the recorded still image will increase. Therefore, it is desired that the digital still camera has a configuration that enables selection of a mode for changing the compression rate, such as a high image quality mode or a low image quality mode.

On the other hand, the recorded image data does not need to be in color, and sometimes it is sufficient to save it as black and white image data.
For this reason, it is preferable that the recording apparatus can record in both black and white and color modes.

SUMMARY OF THE INVENTION An object of the present invention is to select whether to record image data in monochrome or color mode, and to compress image data at an appropriate compression rate according to the selected monochrome or color mode. It is an object of the present invention to provide a digital recording device for still images that can be recorded.

Structure, Action and Effect of the Invention The present invention relates to a data compression means for separately compressing original image data relating to a luminance component and original image data relating to a color component, and compressed image data relating to a luminance component and a color component for one screen. In a still image digital recording apparatus provided with a recording medium for recording each in a separate area, first mode selecting means for selecting one of a monochrome recording mode and a color recording mode, and image data compression rates at different stages When the color recording mode is selected by the second mode selecting means for selecting a plurality of image quality modes respectively corresponding to the first and second mode selecting means, the original image data relating to the luminance component and the color component is changed to the second At the compression rate corresponding to the image quality mode selected by the mode selection means of When the black-and-white recording mode is selected by the first mode selecting means so as to compress each, the original image data relating to the luminance component is color-recorded corresponding to the image quality mode selected by the second mode selecting means. The data compression means is controlled so as to compress at a compression rate lower than that when the mode is selected, and when the monochrome recording mode is selected, the compression of the luminance component is performed over the compressed image data recording area of the color component of the recording medium. It is characterized in that a control means for recording image data is provided.

According to the present invention, it is possible to freely select whether to record the image data in black and white on the recording medium or in color by using the first mode selecting means, and then by using the second mode selecting means. The compression rate of the compressed image recorded on the recording medium can be freely selected. In other words, the quality of the recorded image can be selected.
When the monochrome recording mode is set, the color component data is not required, so only the luminance component is compressed and the compression processing is performed at a compression rate lower than the compression rate of the corresponding color recording mode. Can be improved. In addition, since the recording area of the color component data is used for recording the luminance component data, it is not necessary to increase the image data recording area for one screen even if the data amount increases due to the low compression rate.

When the monochrome recording mode is selected by the first mode selecting means, the original image data relating to the luminance component is
Since the image quality mode selected by the second mode selection means is compressed at a compression rate corresponding to the image quality mode of higher image quality than when the color recording mode is selected, the second mode is selected. The selection means and the compression rate can be used in both the monochrome recording mode and the color recording mode. As a result, the types of mode selection means and the compression ratio can be reduced, and the configuration and the data compression processing control can be simplified.

Embodiments applied to the digital still camera of the present invention will be described in detail below, but it goes without saying that the present invention is also applicable to other types of still image digital recording apparatuses.

Description of Embodiments FIG. 1 is a block diagram showing a part of the electrical configuration of a digital still camera.

A digital signal representing the captured still image is given to the matrix circuit 11, and a luminance signal (signal Y) and a color difference signal (signal BY, signal RY) are created based on this input signal. The luminance signal and the color difference signal output from the matrix circuit 11 are input to the orthogonal transformation unit 12.

The orthogonal transformation unit 12, the normalization unit 13 and the encoding unit 14 constitute image data compression means, but the image data compression processing is performed separately for the luminance signal Y and the color difference signals BY and RY. The data compression process for each of these signals is exactly the same except for the setting of the compression ratio, and therefore will be described below as the image data compression process.

The image data for one screen is composed of N × M pixels, and one pixel is represented by 8-bit data, for example. Such image data is divided into a plurality of blocks in the vertical and horizontal directions of the screen. One block is composed of 8 × 8 pixels, for example.

The image data is subjected to a two-dimensional DCT (Discrete Cosine Transformation) transformation (a type of orthogonal transformation) for each block in the orthogonal transformation unit 12, and its DCT coefficient is obtained. DCT coefficient is a coefficient memory for each block (not shown)
Will be stored in. When the DCT process is completed for all the image data for one screen, the normalization unit 13 then performs the normalization process. In the normalization processing, the DCT coefficient is read from the memory for each block, and this coefficient is divided by the later-described normalization coefficient. The fractional result of this division is quantized by being rounded off. Generally, threshold value processing is performed at the same time as or before this normalization processing. The threshold value process is a process of subtracting a certain threshold value from the DCT coefficient. The subtraction result is set to 0 for the DCT coefficient smaller than this threshold.

The image data to which the orthogonal transformation process and the normalization process have been added in this way is given to the encoding unit 14 and encoded. Encoding includes Huffman encoding, run-length encoding, and the like. Usually, at the same time as or before DCT processing, normalization or encoding, two-dimensional array image data is zigzag scanned and converted into one-dimensional array data. A part or all of the above data compression processing can of course be executed by software processing by the CPU.

The data compression rate in the data compression circuit is specified by the above-mentioned normalization coefficient, threshold value, encoding method, etc.
Here, for simplicity, it is assumed that the compression rate depends on the normalization coefficient.

In any case, the compressed data for one screen is transferred to the memory cartridge 30 together with the normalization coefficient used for the compression, and stored in a predetermined area of the memory built therein. This is because the normalization coefficient is used in decompression processing of compressed data.

The memory of the memory cartridge 30 can store compressed image data for a plurality of screens, and the image data storage area for one screen includes a compressed image data storage area for the luminance Y component and a color difference BY component. Compressed image data storage area,
It is divided into compressed image data storage areas of color difference RY components.

The digital still camera is equipped with a mode setter 15. The mode setter 15 is used for setting two types of modes. One is for selecting the monochrome mode or the color mode, and the key 21 sets the color mode and the key 22 sets the monochrome mode. The other is to select the image quality mode,
This includes high-quality mode, standard mode and economy
There are three modes, which can be set by keys 23, 24, and 25, respectively. Different data compression rates are defined for these image quality modes. The high image quality mode has the best image quality, so the data compression rate is the lowest.
It is set to 2. For example, 7/20 and 1/4 compression ratios are set in the brightness mode and economy mode, respectively.

The above relationship between the image quality mode and the compression rate is the case when the color mode is selected. When the black-and-white mode is selected, a compression ratio one step lower than that in the color mode is assigned. That is, the compression ratio of 1/2 is assigned to the high image quality mode and the standard mode in the monochrome mode, and the compression ratio of 7/20 is assigned to the economy mode. Compression rate 1 / 2,7 / 2
Needless to say, 0, 1/4 are merely examples, and other arbitrary values can be set.

As described above, the image data storage area for one screen in the memory cartridge 30 is the storage area for the Y component, B-
It is divided into a Y component storage area and an RY component storage area (the BY component storage area and the RY component storage area are collectively referred to as a color difference component storage area). When the color mode is selected, Y is set at the compression rate corresponding to the image quality mode selected as described above.
The image data of the component and the color difference component are respectively compressed and stored in the Y component storage area and the color difference component storage area of the memory. When the black and white mode is selected, the image data of only the Y component is compressed at a compression rate one step lower than the compression rate corresponding to the selected image quality mode as described above (excluding the high image quality mode). The compressed data of the Y component is recorded in both the Y component storage area and the color difference component storage area of the memory.

FIG. 2 summarizes the number of bits of the compressed data of the Y component and the color difference component in each image quality mode. The data amount of the original image data is x. The data amount distribution of Y component and color difference component after compression is set to 70% to 30%. Referring to this table, in monochrome mode, when standard mode is set, the total number of bits after compression (7x / 20) corresponds to the number of bits of the Y component (x / 2x7 / 10) in high-quality mode. However, when the economy mode is set, the total number of bits in the economy mode (x / 4) corresponds to the number of bits of the Y component in the standard mode (7x / 20 × 7/10). Is compressed using a compression rate that is one step lower, and even if the amount of data increases slightly, it is possible to record Y component compressed data using not only the Y component storage area but also the color difference component storage area. Becomes

Such control of the compression ratio is performed by the control unit 10 changing the normalization coefficient of the normalization unit 13 according to the setting mode given from the mode setting unit 15. Even if the same normalization coefficient is used, the compression rate may differ depending on the fineness of the image, etc. Therefore, by counting the amount of data after compression and performing feedback control of the normalization coefficient, a predetermined value according to the setting mode can be obtained. The compression ratio is adjusted to

FIG. 3 shows a compression processing procedure in the digital still camera. When the monochrome mode is set, only the standard mode and the economy mode may be set.

The operator sets the type of recording mode and sets the image quality mode using the mode setter 15. When the monochrome mode key 22 is pressed to set the monochrome mode (NO in step 41), the image quality mode set next is determined (step 45). If the image quality mode is set to high image quality mode or standard mode (YE
S), the normalization coefficient is controlled so that the compression process is performed at the low compression rate in the high image quality mode (step 46).

If it is determined that the standard mode or the high image quality mode is not selected (NO in step 45), it is determined that the economy mode is set. As a result, the normalization coefficient is determined so that recording is performed at the standard compression rate in the standard mode (step 47).

When the color mode is set by pressing the color mode key 21 (YES in step 41), the set image quality mode is determined (steps 42 and 43).

If the high image quality mode is set, compression processing is performed at a low compression rate corresponding to that (YES in step 42, step 4
6) When the standard mode is set, the compression processing is performed at the standard compression rate (YES in step 43, step 47), and when the economy mode is set, the compression processing is performed at the corresponding high compression rate ( NO in steps 42 and 43, step 4
Four).

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, and is a block diagram showing a part of the electrical construction of a digital still camera, and FIG. 2 is a diagram showing the relationship between image quality mode and each bit number (compression rate), FIG. 3 is a flow chart showing a compression processing procedure corresponding to the setting mode. 10 ... Control part, 12 ... Orthogonal transformation part, 13 ... Normalization part, 14 ... Encoding part, 15 ... Mode setting device, 30 ... Memory cartridge.

Claims (1)

[Claims] 1. A data compression means for separately compressing original image data concerning a luminance component and original image data concerning a color component, and compressed image data concerning a luminance component and a color component for one screen in separate areas. In a still image digital recording apparatus equipped with a recording medium for recording, a first mode selecting means for selecting one of a monochrome recording mode and a color recording mode, and a plurality of stages corresponding to different image data compression rates of a plurality of stages. When the color recording mode is selected by the second mode selecting means for selecting the image quality mode of No. 1 and the first mode selecting means, the original image data regarding the luminance component and the color component is selected by the second mode selecting means. Each of the first compression When the black-and-white recording mode is selected by the mode selecting means, the original image data relating to the luminance component is compressed at a compression rate lower than that when the color recording mode is selected, which corresponds to the image quality mode selected by the second mode selecting means. Control means for controlling the data compression means so as to compress the compressed image data for the luminance component over the compressed image data recording area for the color component of the recording medium when the monochrome recording mode is selected, Still image digital recording device equipped with.