Image Compress

November 27th, 2017

I’m using IrfanView to Batch Conversion of thundreds of images, which option should I use? 1 or 2?
I’ve tried both and looked at the image quality but can’t seem to tell any difference but what are your opinions?
Option 1 is 100% and set file size to 1MB or below
Option 2 is 85% and no file size is set

Answer #1
Set file size will OVERRIDE the % quality – it will save and re-save in a sort-of binary search until it gets to that desired figure.
For a busy image you can lose a lot of quality.
It depends on what you are after..
If you just want to reduce the size to save space then set it to 80% (still gives excellent quality but saves about 30-50% size from 100%).
If you need to save to a specific size for forum use or such like then you just have to bite the bullet and set to that size. Still note that it will override the quality % setting.
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The reason you don’t see any difference is that probably the 1Mb you set is more than decent for the image – I mean: 85% quality is probably about the same size as the 1Mb setting (so Irfy is saving the 1Mb file AT 85% Q anyway).
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Try an experiment:
Take an image, copy it to another folder, temporary.
Now open it in irfy and re-save it (use <name> test 1) at 1Mb file size.
Repeat about 4 times (<name> test 2..3..4..5) at 500kb, 200kb, 100kb, 50kb.
Now look at the image quality.
You can try the same test using the Q setting – try 90%, 80%, 60%, 40%..
This is how i found that the 80% figure gives be lower size and still decent Q.
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Remember that there are three conditions:
1 – a very busy, detailed image requires a higher %Q to get a better image saved.
2 – an average ‘everyday’ detail image can go to even 70% without seeing any loss of Q
3 – an image with lots of broad flat colour (sky, river, ponds, painted wall, etc) ALSO needs a higher Q% to stop blocks appearing in subtle shading in the broad areas of sky (for e.g.)
Answer #2
So it’s best to set it at 80-85% instead of setting a file size limit
Answer #3
If you are just optimising them for lower space used, yes, go for 85% and check your batch settings as you want them and go for it.
I can save about 50% in many cases – going from 5 Mb to 1.9Mb without any noticable Q loss.
Irfy’s jpg routines are very good.


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