Easy conversion - image formats, currencies and distances

For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

If you're converting between distances (inches, feet, metres, centimetres, metres, furlongs or perches), between currecies (dollars, euros, pounds, roubles, lira) or between graphic file formats (.jpg, .png, .gif, .xbm, .tiff), chances are you'll have any one of a large number of different inputs to change to any one of a large number of different outputs. With - for example - 10 currencies, you'll have 100 (one hundred) possible conversions - and the code will get much bigger and less practical with each new currency added.

The solution is to choose an intermediate standard - for example, to convert the incoming currency to the Euro, then from the Euro to the target currency. That reduces your 100 down to 20 conversions .... and if you had 20 currencies, it would reduce 400 down to 40.

I've got an illustrated example of this techinque on our PHP Techniques Workshop - source code here and the code may be run here. It's also in use on our hotel currency page if guests with to pay in Euros or Dollars - that's based on a more general exchange rate convertor here.

Please consider with this technique that you need to be careful to avoid a loss of precision / information at the intermediate stage.

If your intermediate graphic file standard was .jpg ... it would be a poor choice. .jpg is a lossy standard which makes some compromises. Similarly, an 8 bit image standard would not be suitable.

If your exchange rate tables include commission or are not mid-rate, once again the double conversion I advocate above would lead to an incorrectly rounded result with some loss of data or accuracy. (The ECB tables we use ARE midrate, so there's not an issue!)
(written 2008-05-21)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

H312 - PHP - Tips and Techniques
  [789] Hot answers in PHP - (2006-07-02)
  [917] Syntax checking in PHP - (2006-11-07)
  [1010] Dates, times, clickable diarys in PHP - (2006-12-28)
  [1270] PHP Standalone - keyboard to screen - (2007-07-18)
  [1667] Checking server performance for PHP generated pages - (2008-06-06)
  [1684] Two PHP include files to make easy web site indexing and navigation - (2008-06-21)
  [1958] PHP - Parse error: syntax error, unexpected $end ... - (2008-12-23)
  [1983] Keeping PHP code in database and running it - (2009-01-09)
  [2025] Injection Attack if register_globals in on - PHP - (2009-02-04)
  [2274] PHP preg functions - examples and comparision - (2009-07-08)
  [2478] How did I do THAT? - (2009-10-26)
  [2981] How to set up short and meaningfull alternative URLs - (2010-10-02)
  [4074] A comment on comments in PHP - (2013-04-28)
  [4310] Problem ... I want to print a series of numbered forms - (2014-10-05)
  [4319] PHP - some quick fixes if scripts have issues, and how to use our support - (2014-11-19)
  [4426] FileMaker Day to Unix Time conversion - (2015-02-15)
  [4621] The power of scripting - (2016-01-12)

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Easy conversion - image formats, currencies and distances
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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