Can't say i ever really noticed that, but it's interesting if you put the 1px squares on separate layers, then it seems to resize right using Nearest Neighbor.

(right in the way we seem to think it should)

I can confirm the problem here on Photoshop CS6 Extended x64 using Windows 7.

Adobe has never placed too much emphasis on getting things pixel-perfect in Photoshop - it is more fuzzy and touchy-feely philosophically.  This is not only illustrated by the problem noted above, but also by things like a selection made by a selection tool is often off by a pixel this way or that, paths snapped to things still don't *quite* overlap, etc.

They seem unwilling to change things that have been in the product a while, because apparently when they do so they inadvertently break other things.  And I can't say I blame them...  Given the apparent size of the code base and the extreme age of the software, I wonder what the development cost would be In order to fix something like this across the board, so that every operation really is pixel-perfect.  It might be the kind of thing that a complete redesign from the ground up is needed to fix.  Even then I guarantee you there would be problems.

To Adobe's defense, having been through the development of graphics software myself, I can authoritatively state that actually getting everything pixel-perfect is quite challenging in a world where computing can be done with integers or floating point numbers of various precisions, where no one can quite agree whether a pixel's coordinate identifies its center or one of the corners, where coordinate systems change depending on what subsystem you're using, and where OpenGL documentation recommends you offset your pixels by (0.375, 0.375) in order to ensure they align properly (no kidding).

-Noel

When I scaled it first to 40 and then to 400 it worked. In the past I've noticed similar rounding errors using Illustrator and used scaling in smaller increments as a workaround.

I don't know much about internal calculation and my guess might be completely wrong but from what I vaguely remember about file formats is that they all use compressions which is more  aggressive with calculations related to images where small truncation errors will not cause big social problems.

The same errors occur when scaling a layer with NN interpolation, but something interesting can be seen.

When in transform mode, the displayed result is correct for a 10,000% or 1,000% scale. Only when the transform is commited, do the errors appear in the result.

However, in transform mode, the displayed result is wrong for a 1,100% scale. Only when the transform is commited, does the correct result appear.

Note that very inexpensive software is capable of producing the correct result from NN interpolation, unsurprisingly.

The inaccuracy seems to be in the vicinity of 102.73% no matter what the sizing

Yes, that's what I meant. The workaround is to increase the scale multiple times in smaller increments than all at once.

Curt Y wrote:

 

High precision instruments cost goes exponential with more accuracy.

We're talking about scaling up a raster image (finite discrete pixels) by an integer factor, and using the simplest interpolation method, namely Nearest Neighbour.

Like I posted above, software that costs peanuts is available which can do Nearest Neighbour interpolation correctly. There will be free software, too, I expect.

Gernot Hoffmann wrote:

 

Should the Adobe engineers expect that some idiot expert would

really want to upsample a raster image by factor 10 or 100 in

professional image processing applications?

 

Best regards --Gernot Hoffmann

Is a professional really interested in an idiot's opinion?

Best regards

Robbing people blind is okay, assuming that you are selling a really awesome piece of software. Unfortunately, Adobe is more interested in your wallet than they are in the quality of their own product. They are essentially selling us the same copy of PS from 1988 in a new package.

While Adobe management probably cares little about the quality of their product as long as it makes money (and promises to continue doing so) I guess it is safe to assume that the programmers of Photoshop have an actual interest in providing a good program – after all who would want to be associated with bad products?

And if you fail to perceive the changes and improvements that have been introduced to Photoshop since 1988 then maybe you didn’t know Photoshop 1.

But I’m not contesting that the issue at hand should be addressed.