I have a large (26 x 23) photo collage created for me by a graphic artist. I don't have a printer or a screen large enough to display the whole image at full size (100% scale). So I usually work with it either zoomed out to see the whole image, but at smaller than real life, or zoomed in to work on one part.
I also work with the image in IrfanView because I think its compression algorithm is better than Visio's. But in going back and forth between the two, I discovered a strange inconsistency. In Visio, if I scale it up to full size, I can put a ruler on the screen and get a pretty accurate measurement of what it will be when printed. But in IrfanView, it is three times as large. I also tried it in the SnagIt editor. It also shows it three times as large.
The measurements are in the attached image. I suspect this has something to do with the DPI setting, but I changed in it IrfanView to 900 (from 300) and that did not make a difference.
Can anyone explain what is going on here?
I only looked at this very quickly.
Isn't the issue that the jpeg image is unaware of true scale, so IRView cannot depict it in the scale of the original (please explain how Visio gets this info).
The jpeg's metadata reports 736 x 409 pix and 96 dpi (from where?).
When I scan, or photo, images I always include a reference line of known length that I can measure in image pixels to calibrate the image. IRView has some good tools for that.