Filmless digital camera with selective image compression

• US 5,249,053 A
• Filed: 08/07/1992
• Issued: 09/28/1993
• Est. Priority Date: 02/05/1991
• Status: Expired due to Fees

• Current Assignee: Dycam, Inc. (Fovea Jewelry Holdings Ltd.)
• Original Assignee: Dycam, Inc. (Fovea Jewelry Holdings Ltd.)
• Inventors: Jain, Jaswant R.
• Primary Examiner(s): Groody, James J.
• Assistant Examiner(s): Burgess, Glenton B.
• Application Number:
  US07/926,834
• Time in Patent Office: 417 Days
• Field of Search: 358/209, 358/909, 358/906, 358/335, 358/427, 358/13, 358/432, 358/433, 358/12, 358/135-136
• US Class Current: 348/207.99
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/13 Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
• CPC Class Codes: H04N 19/146 Data rate or code amount at the encoder output
• CPC Class Codes: H04N 19/15 by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
• CPC Class Codes: H04N 19/152 by measuring the fullness of the transmission buffer
• CPC Class Codes: H04N 19/154 Measured or subjectively estimated visual quality after decoding, e.g. measurement of distortion use of rate-distortion criteria H04N19/147
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/18 the unit being a set of transform coefficients
• CPC Class Codes: H04N 19/192 the adaptation method, adaptation tool or adaptation type being iterative or recursive
• CPC Class Codes: H04N 19/30 using hierarchical techniques, e.g. scalability H04N19/63 takes precedence
• CPC Class Codes: H04N 19/60 using transform coding
• CPC Class Codes: H04N 19/86 involving reduction of coding artifacts, e.g. of blockiness
• CPC Class Codes: H04N 19/91 Entropy coding, e.g. variable length coding [VLC] or arithmetic coding
• CPC Class Codes: Y10S 358/906 Hand-held camera with recorder in a single unit

Abstract

In a filmless digital camera, each image is individually evaluated and the compression applied in such manner as to retain maximum quality while fitting the data into the pre-assigned memory. For example, such a camera may have a stated image storage capacity for designated number of images, for example, thirty-two black and white images. In one embodiment of this invention, the image data is generated as analog data and converted into digital data. These data representing one complete image, are divided into small discrete blocks. Each of these blocks is compressed using one of the standard compression methods such as the discrete cosine transform (DCT). Each block of compressed data is then examined and a determination made as to the quality of an image resulting from such compression. If the quality falls below a pre-set standard, the block of data is compressed by an alternate method, for example, by differential coding. The blocks of data that meet the quality requirement, without use of the alternate compression method, are recorded by the first compression method without further processing. Each block of data is coded to indicate the method by which it is compressed. After compression, of the entire image, a computation is mad of the memory storage capacity required for the image. If the required memory is appreciably less than the amount of memory allocated for each image, the compression parameters are adjusted accordingly and the image compressed again. When the memory requirement falls within the established tolerance, the image is recorded. Each block of data is encoded to indicate the method by which it was compressed prior to recording.

Claims

1. In a filmless digital camera in which a predetermined number of images are captured by a CCD, that produces digital data representing said images, and stored in a digital memory having a predetermined allocated capacity per image, the method of compressing the digital data comprising the steps of

dividing the digital data representing one of said images into a series of blocks of predetermined and uniform size each representing a predetermined number of pixels,

compressing said data representing one of said blocks in accordance with a first predetermined algorithm,

computing a measure bearing a pre-established relationship to the creation of artifacts upon decompression of said data,

comparing said measure with a predetermined threshold value and (a) if said measure is less than said threshold, recording said data after compression in accordance with said first algorithm, or (b) if said measure is greater than said threshold, compressing said data as a function of a second algorithm having a characteristic of producing less intense artifacts, and recording said data,

repeating the above process for each block of said image,

measuring the memory capacity required for storage of said image and (a) if said memory capacity exceeds said allocated capacity per image by more than a predetermined amount, modifying the parameters of said first algorithm and changing said threshold to reduce the number of blocks compressed by said second algorithm thereby to reduce the memory utilized to record the compressed image, or (b) if said memory capacity is less by a predetermined amount than said allocated capacity, modifying the parameters of said first algorithm and changing said threshold to increase the number of blocks compressed by said second algorithm thereby to increase the memory utilized to record the compressed image, and

repeating the above process until the memory utilized in recording said image is within predetermined tolerances of said allocated memory.

2. The method as claimed in claim 1 wherein

said first algorithm is the DCT method.

3. The method as claimed in claim 2 wherein

said second algorithm is the differential code method.

4. In a filmless camera in which a predetermined number of successive images are captured by a CCD that produces digital data representing said images and stored in a digital memory having an allocated capacity per image, a method of compressing the digital data prior to recording comprising

dividing the data representing one of said images into a series of blocks or predetermined uniform size wherein each block represents a predetermined number of pixels,

compressing said data representing one of said blocks using a first method of compression,

quantizing the coefficients from said compressed data and counting the number of non-zero coefficients,

comparing the number of non-zero coefficients with a pre-established standard and if said non-zero coefficients are greater than said pre-established standard, compressing said data, prior to compressing said data by said first method of compression by a second and different compression method prior to recording it,

encoding each block of said data to indicate which method of compression has been employed, and

recording the data whether compressed by said first or by said second method of compression.

5. The method as claimed in claim 4 wherein

the first method of compression is the DCT method.

6. The method as claimed in claim 5 wherein

said second method of compression is differential coding.

7. In a filmless digital camera in which a predetermined number of images are captured by a CCD that produces digital data representing said images and stored in a digital memory having a predetermined allocated capacity per image, a method of compressing the digital data comprising the steps of

dividing the digital data representing said image into a series of blocks of uniform size containing a predetermined number of pixels,

successively compressing the data representing each of said blocks by a DCT method with a predetermined scale factor,

determining for each block a coefficient index equal to sum of the high frequency non-zero coefficients derived by said DCT method,

establishing a predetermined threshold number,

determining whether said coefficient index is greater or smaller than said threshold number,

compressing said data for each of said blocks by the differential coding method if said coefficient index exceeds said threshold number by a predetermined amount, and

recording said data.

8. The method as claimed in claim 7 including the step of

encoding each block of data to indicate the particular method by which the data were compressed prior to recording.

9. In a filmless digital camera for capturing and storing data representing a number of still images, a combination comprising

a frame transfer CCD,

a lens system for producing a focused image of a scene to be captured on said CCD,

digital data storage means having a predetermined storage capacity allocated for each image captured by said camera,

means for dividing the data representing one image into discrete blocks of data each having a predetermined number of pixels,

means for computing the DCT of successive blocks of said data,

data compression means including

means for quantizing the DCT coefficients using a predetermined scale factor,

means for determining the sum of selected non-zero coefficients for each of said blocks of data,

means for establishing a relationship between a pre-established threshold and the sum of selected non-zero coefficients in the quantized data representing each of said blocks

means for selecting particular blocks of said data on the basis of the relationship between the pre-established threshold and the sum of selected non-zero coefficients in the quantized data for each of said blocks,

means for compressing each of said blocks of data in accordance with an alternate compression method if said sum exceeds a pre-established threshold, and

means for compressing each of said blocks of data by the DCT method if said sum does not exceed said pre-established threshold, and

means for storing the data in said digital storage means.

10. A camera as claimed in claim 9 including

means for determining the total memory capacity required for said image,

means for modifying said pre-established quantization scale factor and said threshold to increase or decrease the memory storage capacity required to store said image to utilize an increased proportion of the allocated memory, and

means for repeating the foregoing process until the compressed image is within the preset tolerances of the storage capacity allocated for such image.

11. An image comparison system comprising

means for generating a digital block of data representing part of an image to be compressed,

primary compression means for compressing said data block in accordance with a first algorithm that compresses the data by at least 50%,

secondary compression means for compressing said data block in accordance with an alternate algorithm that would on decompression produce less significant artifacts than said primary compression means,

measuring means for measuring the amount of data from said primary compression means representing high spatial frequencies in the image data,

compression control means responsive to said measuring means for deciding whether said data block is compressed by said primary compression means or said secondary compression means, and

means for recording the compressed data block.

12. The system as claimed in claim 11 wherein

said primary compression means uses the DCT algorithm.

13. The system as claimed in claim 11 wherein

said compression control means is controlled as a function of the number of high frequency terms in the compressed data from said primary compression means.

14. The system as claimed in claim 13 wherein

said primary compression means uses the DCT algorithm,.

15. An image compression system comprising

means for producing a block of digital data representing a portion of an image,

quality factor control means,

primary compression means under the control of said quality factor control means for compressing said data block in accordance with a first algorithm that reduces the data in spatially high frequencies but which upon decompression produces visually objectionable errors from bright points in said image,

secondary compression means for compressing said data block in accordance with an alternate algorithm that on decompression does not produce objectionable errors from bright spots in said image,

measuring means for measuring the amount of data from said primary compression means resulting from high spatial frequencies in the image data,

compression control means responsive to said measuring means for controlling whether said data block is compressed by said primary compression means or said secondary compression means.

16. An image compressing system as claimed in claim 15 including

means for adjusting the control value of said quality factor control means, and wherein

said compression control means is responsive to the control value of said quality control factor.

17. An image compression system as claimed in claim 15 including

means for producing a plurality of blocks of said digital data which together represent an entire image,

memory measuring means for determining the memory required to store all of said blocks after each has been compressed by either said primary or said secondary compression means,

compression adjustment means for (a) decreasing the amount of compression of all of said blocks if the required memory exceeds a predetermined value, or (b) increasing the amount of compression of all of said blocks if the required memory is less than said predetermined value by a predetermined amount, and

means for repeated operation of said compression adjustment means until said required memory is less than said predetermined value by no more than preset tolerance.