What does "Real size" mean?

thricipio · Post by **thricipio** » Tue Apr 15, 2008 3:23 pm

When viewing an image, and selecting "Real size," I get a view of my (1280x800) image at 32%. I would have expected to get a zoom level of 100%. I assume XnView is working properly and I simply lack the proper understanding of what "Real size" means.

Could anyone explain this to me?

Thanks.
--Thri

marsh · Post by **marsh** » Tue Apr 15, 2008 6:28 pm

I think it is a representation of what the 'print size' would be like at 100%.

thricipio · Post by **thricipio** » Tue Apr 15, 2008 9:37 pm

marsh wrote:I think it is a representation of what the 'print size' would be like at 100%.

Hmmm... I suspect you're right. The thought had occurred to me after I posted my question.

Thing is, though... it's size on the screen is certainly smaller than 4x6" which is the size of the prints that accompanied the CD from which I copied the image files.

Anyway, thanks for the help.
--Thri

oops66 · Post by **oops66** » Tue Apr 15, 2008 11:39 pm

No, I think the "real size" (100% - hotkey "*") is the limite of resolution of human eyes.
See Circle of confusion here :
http://en.wikipedia.org/wiki/Circle_of_confusion
Visual acuity. For most people, the closest comfortable viewing distance, termed the near distance for distinct vision (Ray 2002, 216), is approximately 25 cm. At this distance , a person with good vision can usually distinguish an image resolution of 5 line pairs per millimeter (lp/mm), equivalent to a CoC of 0.2 mm in the final image.

thricipio · Post by **thricipio** » Wed Apr 16, 2008 12:04 am

Whoa! A whole new level of esoterica I would have never imagined!

Cool!

--Thri

JohnFredC · Post by **JohnFredC** » Wed Apr 16, 2008 3:18 pm

That's a wonderful link! Thanks!

OT:

You can use the same methodology to determine that your 1080p Hi-Def television has probably "way" too small a screen.

oops66 · Post by **oops66** » Thu Apr 17, 2008 1:56 pm

Yes John, or by this way it's easier (1.25 lines per minute of arc)

Pierre, would it be possible to have an option to attrib at the hotkey "*" (real size) the approximative limite of resolution of human eyes (for common LCD screens: 19 inch, with the dot pitch=0.25mm & distance user/screen = ~60cm calculated with a resolution limite = 1.25 lines per minute of arc, or like it is now, the representation of what the 'print size' would be like at 100% ???

http://en.wikipedia.org/wiki/Eye
Equivalent human eyes resolution:
A maximum resolution of the human eye in good light of 1.6 minute of arc per line pair will correspond to 1.25 lines per minute of arc. Assuming two pixels per line pair (one pixel per line) and a square field of 120 degrees, this would be equivalent to approximately 120×60×1.25 = 9000 pixels in each of the X and Y dimensions, or about 81 megapixels...