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Questions and Answers
Which of the following is NOT a characteristic of JPEG-LS?
Which of the following is NOT a characteristic of JPEG-LS?
- Utilizes the Discrete Cosine Transform (DCT) (correct)
- Examines neighboring pixels to predict the current pixel
- Designed to be simple and fast
- Employs quantization in a limited way for near-lossless compression
Vector quantization is only suitable for image compression and not for sound compression.
Vector quantization is only suitable for image compression and not for sound compression.
False (B)
What data type is commonly compressed utilizing vector quantization that originates from an analog source?
What data type is commonly compressed utilizing vector quantization that originates from an analog source?
Digitally Sampled Analog Data (DSAD)
In JPEG-LS, the algorithm selects a probability distribution out of several such distributions and uses that distribution to encode the _________ _________ with a special Golomb code.
In JPEG-LS, the algorithm selects a probability distribution out of several such distributions and uses that distribution to encode the _________ _________ with a special Golomb code.
Match the following steps related to the LBG algorithm with their descriptions:
Match the following steps related to the LBG algorithm with their descriptions:
What is the primary reason the ISO developed JPEG-LS?
What is the primary reason the ISO developed JPEG-LS?
Adjacent items in an image and in digitized sound are generally uncorrelated.
Adjacent items in an image and in digitized sound are generally uncorrelated.
What algorithm is the basis for many vector quantization methods used for image and sound compression?
What algorithm is the basis for many vector quantization methods used for image and sound compression?
In the context of the LBG algorithm, image blocks are denoted by $B_i$, and these blocks are also referred to as __________ __________.
In the context of the LBG algorithm, image blocks are denoted by $B_i$, and these blocks are also referred to as __________ __________.
What happens in the decoder during the vector quantization procedure once the code index of the input vector is received?
What happens in the decoder during the vector quantization procedure once the code index of the input vector is received?
The initial value of 'k' in the LBG algorithm represents the final iteration count and cannot be zero.
The initial value of 'k' in the LBG algorithm represents the final iteration count and cannot be zero.
In vector quantization, what is the primary advantage of compressing strings of symbols rather than individual symbols?
In vector quantization, what is the primary advantage of compressing strings of symbols rather than individual symbols?
In Step 3 of the LBG algorithm, the algorithm halts if the condition $(D^{(k-1)} - D^{(k)}) / D^{(k)} \leq \epsilon$ is met, where $\epsilon$ represents the _________ _________.
In Step 3 of the LBG algorithm, the algorithm halts if the condition $(D^{(k-1)} - D^{(k)}) / D^{(k)} \leq \epsilon$ is met, where $\epsilon$ represents the _________ _________.
Which step in the LBG algorithm adapts the codebook entries to fit the particular image being compressed?
Which step in the LBG algorithm adapts the codebook entries to fit the particular image being compressed?
JPEG-LS uses arithmetic coding for its compression.
JPEG-LS uses arithmetic coding for its compression.
What type of code is used in JPEG-LS to encode the prediction error?
What type of code is used in JPEG-LS to encode the prediction error?
In vector quantization, the encoder finds the closest _______ _______ to the input vector and outputs the associated index.
In vector quantization, the encoder finds the closest _______ _______ to the input vector and outputs the associated index.
What does $D^{(k)}$ represent in the LBG algorithm?
What does $D^{(k)}$ represent in the LBG algorithm?
Vector Quantization is a lossless compression method.
Vector Quantization is a lossless compression method.
In JPEG-LS, the previously seen neighbors of the current pixel are used as the_____of the pixel.
In JPEG-LS, the previously seen neighbors of the current pixel are used as the_____of the pixel.
Flashcards
JPEG-LS
JPEG-LS
Standard developed by the ISO for lossless or near-lossless compression of continuous-tone images; known for being simple and fast.
Vector Quantization
Vector Quantization
A method used for both image and sound compression, primarily on data digitized from analog sources.
Digitally Sampled Analog Data (DSAD)
Digitally Sampled Analog Data (DSAD)
Data that has been digitized from an analog source
LBG Algorithm
LBG Algorithm
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Training Vectors
Training Vectors
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Study Notes
- The lossless mode of JPEG is inefficient and often not implemented
- The ISO decided to develop a standard for lossless/near-lossless compression of continuous-tone images
- This resulted in what is known as JPEG-LS
- JPEG-LS is designed to be simple and fast for compression
JPEG-LS Characteristics
- It does not extend or modify JPEG
- It avoids DCT and arithmetic coding
- It uses quantization minimally, only in near-lossless mode
- It examines neighbors of the current pixel to decide context
- Pixel context is used to predict the pixel and select a probability distribution
- The prediction error is encoded using a special Golomb code
- A run mode encodes the length of identical pixel runs
Vector Quantization
- Vector quantization is a generalization of scalar quantization and is used for image and sound compression
- In practice, vector quantization is used to compress data digitized from analog sources, like sampled images and scanned images
- This data is called Digitally Sampled Analog Data (DSAD)
- Vector quantization is a lossy compression method
Vector Quantization Facts
- Compression methods that compress strings (rather than individual symbols) can produce better results
- Adjacent items in an image and digitized sound are correlated
- Near neighbors of a pixel P likely share values
Vector Quantization Procedure
- The encoder finds the closest code vector to the input vector to output the associated index
- The same codebook is used on the decoder side
- If the code index of the input vector is received, a simple table lookup is performed to determine the reconstruction vector
LBG Algorithm for Vector Quantization
- The LBG algorithm is the basis of many vector quantization methods for image and sound compression
LBG Algorithm Steps
- Step 0: Select a threshold value and set k = 0 and D(-1) = ∞. Start with an initial codebook with entries C(k).
- Step 1: Pick a codebook entry C(k). Find all image blocks Bmthat are closer to Ci than to any other Cj
- Step 2: Select an i and calculate the distortion D(k) between codebook entry C(k) and the set of training vectors (partition) Pfound for it in Step 1 and calculated the average
- Step 3: If (D(k-1) – D(k))/D(k) ≤ ∈ halt and the ouput is the last set of codebook entries C.(k).
- Step 4: Increment k by 1 and calculate new codebook entries C(k); each equals the average of the image blocks (training vectors) in partition P(k-1) that was computed in Step 1.
LBG Algorith Example
- Assumes an image includes 24 pixels, arranged in 12 blocks with 2 pixels each
- The 12 points concentrate in four regions
- An initial codebook is selected with four entries
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