Category: technology

Image compression

 

GIF’s (Patented format – Patent expired in 2000)

– Supported animated GIF’s too

 

PNG (Patent Free)

– 8 Bit color scheme + Rich true color pallette + Alpha transparency

– Delta Encoding – Represent pixels as delta of neighbour. 000000020000, and then compress 0’s. Represent all adjacent 0’s by say A

 

JPG

– 8*8 pixel boxes.

– DCT

– Quantization – neighbours are rounded and therefore Lossy data compression

  • Baseline – Data writte blocks after blocks. Therefore rendering also from baseline (say top left to right and down)
  • Progressive – Random blocks are written. Read also in same manner, like FB(mobile) does – something is visible, even if hazy initially,

 

WebP – Supported by Google

JPGxR – Supported by Microsoft.

 

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3G to 4G

3G uses Circuit Switching, upto 1.5 Mbps of data transfer speeds

4G on packet based network – IP based network, flexible bandwidth upto 100 Mbps

Pre 4G – WiMax & LTE (Long Term Evolution)

reCAPTCHA

How humans are involved in helping digitization of books, http://recaptcha.net/learnmore.html

 

“reCAPTCHA improves the process of digitizing books by sending words that cannot be read by computers to the Web in the form of CAPTCHAs for humans to decipher. More specifically, each word that cannot be read correctly by OCR is placed on an image and used as a CAPTCHA. This is possible because most OCR programs alert you when a word cannot be read correctly.

But if a computer can’t read such a CAPTCHA, how does the system know the correct answer to the puzzle? Here’s how: Each new word that cannot be read correctly by OCR is given to a user in conjunction with another word for which the answer is already known. The user is then asked to read both words. If they solve the one for which the answer is known, the system assumes their answer is correct for the new one. The system then gives the new image to a number of other people to determine, with higher confidence, whether the original answer was correct.”