1. Image compression reduces storage requirements by compressing images to reduce file sizes while retaining essential information. 2. Common image file formats include TIFF (uncompressed), JPEG (lossy compression), GIF (lossless compression suitable for web but limited colors), PNG (lossless compression for web that allows more colors than GIF), and RAW (unprocessed camera files). 3. Standards like JPEG, MPEG, and H.261 were developed to compress images and video for efficient storage and transmission by applying techniques like the discrete cosine transform, quantization, and entropy encoding.

1. IMAGE COMPRESSION
Presented By,
M.Ramya,
MSc(CS&IT),
Nadar Saraswathi college of Arts & Science,
Theni.

2. INTRODUCTION
• Audio, image and video require vast amounts of data.
 320x240x8bits grayscale image: 77Kb
 ‰1100x900x24bits color image: 3MB
 ‰640x480x24x30frames/sec: 27.6 MB/sec
• ‰Low network’s bandwidth doesn't allow for real time video transmission.
• ‰Slow storage devices don't allow for fast playing back ‰Compression
reduces storage requirements.

3. TYPES OF IMAGE
There are 5 main formats in which to store images.
 TIFF
 JPEG
 GIF
 PNG
 Raw image files

4. TIFF
• TIFF stands for Tagged Image File Format.
• TIFF images create very large file sizes.
• TIFF images are uncompressed and thus contain a lot of detailed image
data.
• TIFFs are also extremely flexible in terms of and content.
• TIFF is the most common file type used in photo software as well as page
layout software.
• TIFF contains a lot of image data.
• TIFF file types ending in .tif

5. JPEG
• JPEG stands for Joint Photographic Experts Group, which created this
standard for this type of image formatting.
• JPEG files are images that have been compressed to store a lot of
information in a small-size file.
• A JPEG is compressed in a way that loses some of the image detail during
the compression in order to make the file small.
• JPEG files are bad for line drawings or logos or graphics, as the
compression makes them look “bitmappy”.
• JPEG file types ending in .jpg

6. GIF
• GIF stands for Graphic Interchange Format.
• This format compresses images but, as different from JPEG, the
compression is lossless.
• GIFs also have an extremely limited color range suitable for the web but
not for printing.
• This format is never used for photography, because of the limited number
of colors.
• GIFs can also be used for animations.
• GIF file types ending in .gif

7. PNG
• PNG stands for Portable Network Graphics.
• It also allows for a full range of color and better compression.
• It’s used almost exclusively for web images , never for print images.
• For photographs , PNG is not as good as JPEG , because it creates a larger
file.
• It was created as an open format to replace GIF , because the patent for GIF
was owned by one company and nobody else wanted to pay licensing fees.
• PNG file types ending in .png

8. RAW IMAGE FILES
• Raw image files contain data from a digital camera.
• The files are called raw because they haven’t been processed and therefore
can’t be edited or printed.
• Raw files usually contain a vast amount of data that is uncompressed.
• The size of a raw file is extremely large.
• They are converted to TIFF before editing and color-correcting

9. RECENT COMPRESSION STANDARDS

10. JPEG
JPEG Modes of Operation ‰Sequential
DCT
The image is encoded in one left-to-right, top-to-bottom scan
‰Progressive DCT
The image is encoded in multiple scans
Hierarchical
Encoding at multiple resolutions
Lossless
Exact reproduction

11. JPEG BLOCK DIAGRAMS

12. JPEG ENCODER
Three main blocks
 ‰Forward Discrete Cosine Transform (FDCT)
‰Quantizer
 ‰Entropy Encoder
‰Essentially the sequential JPEG encoder ‰
Main component of progressive, lossless and hierarchical encoders ‰
For gray level and color images

13. JPEG DECODER
The same steps in reverse order
The binary sequences are converted to symbol sequences using the
Huffman tables
‰F’(u,v) = Fq(u,v)Q(u,v)
‰Inverse DCT

14. HIERARCHICAL JPEG
Produces a set of images at multiple resolutions ‰
Begins with small images and continues with larger images
The reduced image is scaled-up to the next resolution and used as
predictor for the higher resolution image

15. MPEG
• The Moving Picture Coding Experts Group (MPEG) is a working group for
the development of standards for compression, decompression, processing,
and coded representation of moving pictures and audio
• ‰MPEG groups are open and have attracted large participation

16. MPEG FEATURES
• Random access
• ‰Fast forward / reverse searches
• ‰Reverse playback
• ‰Audio – visual synchronization
• ‰Robustness to errors
• ‰Auditability
• ‰Cost trade-off

17. MPEG ENCODING
• I frames are JPEG compressed
• ‰P, B frames are encoded in terms of future or previous frames
• ‰Motion vectors are estimated and differences between predicted and actual
blocks are computed ‰
These error terms are DCT encoded
 ‰Entropy encoding produces a compact binary code
‰Special cases: static and intracoded blocks

18. px64
• H.261 (px64) was designed for data rates which are multiples of 64kbit/s
and is sometimes called px64kbit/s (p is in the range 1-30).
• These data rates suit ISDN lines , for which this video code was designed
• Intended for videophone and video conferencing systems
• Compressed data stream.
p*64 Kbits/s , p = (1,……,30)
• Video compression for video conferences
Compression in real-time
Targeted to ISDN

19. H.261 (Px64) RESOLUTION
• Common Intermediate Format (CIF)
• Quarter CIF (QCIF)
CIF QCIF
Lines/frame pixels/line Lines/frame pixels/line
Luminance (Y) 288 352 144 176
Chrominance (Cb) 144 176 72 88
Chrominance (Cr) 144 176 72 88