Relative zoom calculation: a drawback

[j7n]

I can't tell for sure which one of these samples have 50% zoom. The bigger one appears better, but perhaps it's because it is significantly higher res.

In the past I already presented a sample where the aliasing becomes apparent (Photoshop 5 Balloons). This effect is also sometimes apparent during zoomed video playback using simple hardware bilinear.

Here's another picture at 50 and 52 percent (420 kB each, PNG).
- http://j7n.sytes.net/temp/iv-radio-mast-50.png
- http://j7n.sytes.net/temp/iv-radio-mast-52.png

The issue has nothing to do with conventional monitors (apart from the fact that your samples have been cleartyped). We're discussing a type of resampling.

[beerslayer]

Why anyone needs to zoom to exactly 200% is beyond me. Who cares if it is 200% or 195%? If you turn off the status line you will soon forget about it.

I disagree. At least on my system, the image looks much cleaner at exactly 200% than it does at 195%. In theory at least, zooming to 200% ought to be faster anyway... just double each pixel! (Yes, I know it isn't quite that simple, but that would at least be a useful approximation.)

Zooming to 100% is simple — just press Control H.

This doesn't work in full-screen mode if you have all images set to "Fit to screen". For example, say you are opening an image in full-screen mode that is way too big to fit on the screen at actual size, and IrfanView initially displays it at, say, 37%. You can hit the + or - keys to zoom in or out, but Ctrl-H brings it back to 37%, not to 100%. I have found no easy way to get to exactly 100% other than changing Preferences to display all images as original size, which is not the solution I am hoping for.

[ChuckE]

Why anyone needs to zoom to exactly 200% is beyond me. Who cares if it is 200% or 195%? If you turn off the status line you will soon forget about it.

And I disagree, as well. One of the things I like to do is to zoom in a step or two, or more, to see something and then zoom back out to get back exactly where I had started. No approximations. No pressing of other keys (like Ctrl-H) to get to 100% (which is itself a problem when images are larger than the screen), and then zoom from there (grrrrr).

[Bhikkhu Pesala]

This doesn't work in full-screen mode if you have all images set to "Fit to screen".

In full screen mode the shortcut "1" will zoom to 100%.

One of the things I like to do is to zoom in a step or two, or more, to see something and then zoom back out to get back exactly where I had started.

No argument there. Zoom in and zoom out should go to same zoom level that you started with. It does in DrawPlus, even though the step is a Geometric progression.

As already agreed, a list of preset steps is the best solution. However, these should not be in an arithmetic progression as it is next to useless at opposite ends of the scale — say 20%, 10% and 800% and 810% or 100% 50% stop and 800% 850%

[ChuckE]

One of the things that Microsoft Word does "right" is their enlarging and shrinking of selected text font size.

You can select text and press:
Ctrl-< or Ctrl-> to change the size one most likely step at a time.
(For example, if you are already at font size 48, then up or down will put you at 72 or 36.)

OR!
Ctrl-[ or Ctrl-] for changing the font size one point size with each press.
(For example, if you are already at font size 48, then up or down will put you at 49 or 47.)

The reason I am mentioning this is that I have suggested that IrfanView have BOTH zoom types, relative and fixed. Just have a different way of selecting one or the other.

Heck, it could also be three types of zoom, relative, fixed, and user defined (where the user can set up stepped zoom levels such as 10, 20, 50, 100, 200, 300, 400, 500% etc.). What the heck? would that not settle all problems that seems all of us users have with one way over the other?

Irfan, are you not listening?

[beerslayer]

In full screen mode the shortcut "1" will zoom to 100%.

I did not know about this shortcut - thanks. Interesting that I've been using IrfanView for years and never found this information in the Help file (yes, I've found it now). Perhaps these options could be listed in the menus for the benefit of idiots like me who haven't memorized every word in the Help file...?

No argument there. Zoom in and zoom out should go to same zoom level that you started with.

I do agree with this; however...

As already agreed, a list of preset steps is the best solution. However, these should not be in an arithmetic progression as it is next to useless at opposite ends of the scale — say 20%, 10% and 800% and 810% or 100% 50% stop and 800% 850%

I don't know that this has been "already agreed". Seems that there's been significant disagreement on this point.

I guess I'm having trouble understanding why anyone would be using IrfanView to view an image at 800%. A lossy format like .jpg is so pixelated at 800% that it is virtually unusable. The only time I can imagine needing to view a .jpg at 800% is if I'm editing it, which I wouldn't be using IrfanView for anyway.

I'd rather have a simple, predictable, *consistent* effect. If I need to get from 100% to 300%, and I have zoom step set to 25%, I can slap the + key eight times faster than I can calculate in my head (or look up in a help file) how many times I need to press it under a geometric zoom scheme.

[j7n]

Irfan, are you not listening?

There has been no indication that this is the case.

I guess I'm having trouble understanding why anyone would be using IrfanView to view an image at 800%. A lossy format like .jpg is so pixelated at 800% that it is virtually unusable.

Any format, except vectors, is "pixellated" at 800%. One use of zoom might be to check if the given sample is JPEG.

[Bil]

Blooming Luddites!

The current method is much better, though it does need adjustment so that the zoom out keeps in step with the zoom in.

If you have already zoomed in 800% to an image and zoom in once more, zoom 10% is not a lot of use. A geometric progression is more useful. If you zoom out to 20%, then a 10% step is near to useless.

The zoom slider control in Draw Plus works really well. The image is resampled too, and much faster than in Irfan View. It has a zoom range of 2% to 5,000%.

"The current method is much better..." -
NO NO NO - It is better for you!

I DON'T like it!
I think to revert to older version!
(it is a pity - I very much like IrfanView)

Many people like the old-fashioned predictable zoom.
I like zoom factors of 50, 100, 150, 200, ... 400%, ...

I press + or - for a long time and use autorepeat (30 chars/sec) to zoom.
If I miss the zoom of e.g. 400% I want to be able (as before) to press
- or + to go EXACTLY to 400%.


PLEASE, give the people a choice - give us an option in preferences
to choose between the "new" and "old" zoom methods.
(so that you and I and everybody will be happy)


And maybe while zooming the Shift modifier (Shift_+ & -) can be used for:
1) temporarily using the other (not set in preferences) method
or
2) bigger (double) zoom step

[Bil]

Again, not really, since IrfanPaint only requires a call from IrfanView, which was available (since the middle of July '07) as a modified v4.0 from MItaly.

The modified i_view32.exe, the main IrfanView executable, which has the <F12> call for IrfanPaint, does not care which version of the IrfanPaint is installed. Just that the plug-in is in the correct place.

So, you can get the modified v4.0 from MItaly's website, and use the latest version of his really nice plug-in, IrfanPaint.

I've reverted to v4.00 using the i_view32.exe from the .zip

http://www.mitalia.net/irfanpaint/download.php?redirect=packets/full/IrfanPaint_0.4.5.47_bin%2BIV.zip

which is the last with v4.00 of the i_view32.exe in it.

I'm happy now with the re-invented, good, old-fashioned, predictable zoom.

I'll wait for the next version in hope it will give us a choice!