Originally posted by roygoh
I feel that one factor that is often neglected or not scientifically associated in the discussion of ppi is the viewing distance.
Agree absolutely. That's what lead us into the debate.
From JC physics class I remember that the resolving power of the human eye (or any optical device) can be expressed as the smallest angle between 2 point light sources than can be barely distinguished as separate light sources. This value most likely varies from person to person. (For me, I know this angle differs a lot between the times when I am wearing my glasses and when I am not!). Anyway, I do not know what ange of this value applies to an avverage person with good eyesight.
Oh, why I never learn that 20 years back in JC? I guess we have generation gap.
Now for a 300ppi print, when viewed at 50cm, the angular separation between 2 adjacent pixel centres is 0.0097 degrees (ATAN (pixel distance / viewing distance)). Would an average person have significantly better resolving power than this angle? If yes, then he will more likely be able to tell the difference between a 300ppi and a 600 ppi print. If the resolving power is weaker (larger angle than 0.0097 degrees), then he will not be able to tell the difference between 300 ppi and 600 ppi - at the viewing distance of 50cm.
As the viewing distance decreases, the angular separation between pixels increases, thus making it easier for one to tell the difference. At the extreme, you can look at the print with a loupe and be able to distinguish the individual dots used to form the pixels.
What do you think?
I can't agree more.
So KamWeng, from your experience, what is the critical distance for you beyond which you will not be able to tell the difference between 300 and 600 ppi?
Maybe beyond 30cm or more. I have a strange habit when examining a print which I think normal person won't look at that way : first I look from a distance of around 30cm (not 50cm for me) and then
at a distance of ~10cm without my glasses, moving the print back and forth until I can see it clearly (manual focus I call it). In this way, I can see the details which most of my colleagues I asked could not tell.
I'm a perfectionist. So maybe it's myself who're trying to find fault. As I've pointed out in my previous post, maybe I was asking for too much. I know people normally won't look at a print that careful. I'm just trying to find out the ppi that possibly make prints sharper (in order to impress people), but since most of you don't see that there's difference, there's no point for me to print 'sharper'.
Also, related to my initial question, do you notice any degradation in colour resolution when you print at 600ppi?
No. I can only notice the increment in details on fine objects i.e. the titles of the books on a book shelve (
) , tree leaves etc.
By the way, regarding your analogy to CD, regardless of the type of audio processing, the final CD format is still 44.1kHz 16-bit, which correspond better to the print resolution. So even if you can tell that one CD sounds better than the other (even a difference in clarity and detail heard), it is not a good analogy to compare 300 and 600 ppi, which is a difference in the resolution of the fianl media. A better analogy would be to compare 44.1kHz/16-bit against 96kHz/20 bit.
No comment. I was just replying the guy with his own example. I didn't analyzed further.
Your open and friendly
discussion is most welcomed.