I have large JPEG images of around 2000 x 1500 (a few Megabytes in size).
I wish to resize them for display to 200 x 150 (ideally 10KB or so) in a phone app.
I’d like to know what would be the best steps given I want a reasonably small size and as good a quality (given the maximum size).
Some options:
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First reduce dimensions to exactly 200×150 and then if size is not 10KB yet, to change the quality of JPG until I get the correct size. Is it a good practice to create the exact thumbnail size I need?
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OR, reduce dimensions to a slightly larger thumbnail than required (eg. 400 x 300, or 300 x 225 ETC) – is there a “best practice” to get a photo size larger than the one you are displaying? Then change the quality of JPG until size is obtained.
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Resize to much larger than 200×150. Just change quality of JPG until it hits 10Kb or less.
A related question: for JPEG, once I reduce the dimensions (pixels size), I wish to adjust the quality of the JPG output until a target size is obtained. Can this only be done by trial and error? Currently, I try a higher % first then keep lowering it until the desired size is reached, but it’s not ideal as it uses quite a fair bit of CPU cycles.
Is there an approximate formulae that will tell me to get from 50KB to 10KB, I need to drop from 100% JPG quality to 79%, for example.
Example: after I reduce the dimensions, a 4MB photo becomes 0.5MB. Is there a formula by which each % of a reduction in JPG quality will result in how many % of the JPG size, so that I can get as close to 10KB without too much trial and error?
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