All about JPG
Results of JPG test
Saved same picture over and over using IrfanView. I had previously compared with Paint Shop Pro and IrfanView makes a bit smaller file with no apparent loss in quality. I had the Quality set at 100%.
Started at 295955
Bytes
Loss
295955
295595 360
295442 153
295245 197
295202 43
295019 83
294956 63
294857 99
294802 55
294761 41
As one can see, you lose a bit each time. There doesn't seem to be a definite pattern.
Switched to Windows Paint using the above file at 294761 bytes.
48806 Big Loss
48795 6
48793 2
Paint appears to have 75% built in. With IrfanView, a 70% setting reduced it to 42K (see below).
After it reduced it the first time, Paint didn't reduce very much after that.
I guess that, once you have applied that compression, you can't go much further.
Who knows!
When I took the same file and did Save As using IrfanView, here are the resultant file sizes:
Orig 293K
90% 88K
80% 55K
70% 42K
60% 35K
50% 30K
40% 25K
30% 21K
I couldn't see much difference in picture quality between 100% and 70%. Lower than that saw some drop off. It depends on the picture. Some pictures would be acceptable down to 40% or 50% depending on the circumstances. If you are sending something dumb in an email, it would quite often be useful to reduce the size. Under 30% is out of the question.
RECOMMENDATION: It would be a good idea to take a picture, Save As 90, 80, etc. file names corresponding to the percentage. Then do a slide show of all of them and see if you can tell the difference. Be sure to use the original each time: don't use the one you just saved - that's reducing a reduction which doesn't work.
CONCLUSION: I have always arbitrarily left my Quality on 80%. However, that 80% sticks with you every time you save the file. If you do that very often, you'll lose a bunch of quality. As we just saw, even at 100% you lose a little each time. So, from now on, I'll keep it at 100% and, when I go to use it, I'll Save As to the size appropriate for the occasion.
There are those who suggest keeping the original file. If you have lots of hard drive or you burn to a CD, that isn't a bad idea. Then you can always go back and get it nice and fresh - and original.
BEWARE OF WINDOWS PAINT:
Yes, it will edit your JPG file; but, when you get done, it will reduce it that 75% dropping it from 293K to 48K.
HOWEVER, I just figured out how to fool it. I went to IrfanView (substitute your own picture program) and changed it to a BMP.
I closed IrfanView and pulled up the BMP file in Paint. I made a change - put a black dot in the
sky - then I saved the BMP file. I closed Paint and went to IrfanView and opened the file.
I then did Save As to a JPG. I lost only about a third of a K which is nothing. So that's the way to do it.
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