1. Explain the JPEG modes of operations?
Following are the JPEG operation modes:
- Lossless Mode: Every pixel in the image is encoded even though the compression ratio is low.
- Sequential Mode: A single scan from left-to-right and top-to-bottom compresses the image.
- Progressive Mode: Multiple scans are used to compress the image. The transmission time is long.
- Hierarchical Mode: Multiple resolutions are used to compress the image. Hence the lower resolution is accessed first which does not require the decompressing the whole resolution of the image.
2. What is Discrete Cosine Transform?
1. It is similar to Fast Fourier Transform.
2. The frame blocks of size 8x8 or 16x16 pixels are represented as frequency components.
3. This transforms into frequency domain by implementing standard formula.
1. Two successive video frames often have small differences.
2. MPEG standard has a standard to reduce this temporal redundancy.
4. What is Reduction of the Resolution?
1. Performs the conversion of RGB-color space into YUV color components.
2. The chrominance components U and V can be reduced to half of the pixels in the horizontal direction.
5. Do you know about 3-level Hierarchical JPEG Encoder?
- Down-sample the factors of resolution by 2 for each dimension. For example - ,Reduce the 640 x 480 resolution to 320 x 240 resolution.
- Code the smaller image with another JPEG mode.
- Decode the image and up the sample encoded image.
- Encode the difference between the decoded image and the original image.
- The above process can be repeated for multiple times.
- This process provides high quality images with low resolution display.
6. Explain some major steps for JPEG compression?
Following are the major steps that are involved in JPEG compression:
- Discrete Cosine Transformation.
- Quantization.
- Zigzag Scan.
- DPCM on DC component.
- RLE on AC Components
- Entropy Coding.
7. Explain the features of JPEG 2000 standard?
Following are the JPEG 2000 features.:
- Compression performance is at low bit-rate.
- Both lossless and lossy compression is performed with a single code stream.
- The transmission in noise environment can be done with low bit-error rate.
- It is applicable for both gray and color images.
- Bi-level imagery, natural imagery and computer generated imagery is applicable for gray and color images.
- It is interactive with MPEG-4 standard.
- Wavelets will be replaced with Discrete Cosine Transform
- MPEG-2 is one of the international standards for compressing video signals.
- Videos can be compressed prior to transmission or storage.
- The approximate compression ratio is 50:1 of the digital size.
- MPEG-2 standard is widely implemented in digital TV transmission with 200 million decoders.
- MPEG-2 standard exploits the redundancies in the original signal.
9. Do you know what are the desirable properties of a speech coder?
Following are the desirable properties of speech coders:
- Low Bit-Rate.
- Low Memory Size
- Low Coding Delay
- High Speech Quality
- Robustness Across Different Languages / Speakers
- Robustness in the Presence of Channel Errors
- Good Performance on Non-Speech Signals, like telephone signaling.
- Vocoder is one of the audio processors
- The characteristic elements of an audio signal are captured by Vocoder.
- These characteristic signals are used to affect the other audio signals.
- It is widely used in speech synthesis.
- A component known as Formant describes the frequency of a sound and noise components that are associated.
- The audio output of Vocoder has synthesized sound that is modulated by a filter.
- The synthesized sound is pulsed to the tempo of the user input voice with the tonal characteristics of the voice.
