Relative zoom calculation: a drawback

[Bhikkhu Pesala]

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%.

[j7n]

We are not talking about vector graphics. Raster is can only be viewed precisely at 100%, 50%, 25% (the word "at" can't actually be used here) and magnified for thorough analysis of the pixels – but that's more for an editor like PSP.

With zoom step of 25% you can quickly get down from 800 with a fast keyboard repeat rate. 1.5 seconds.

[Bhikkhu Pesala]

Don't be misled by the name DrawPlus. It can also use bitmaps and bitmap fills.

I fail to see why anyone needs to have round numbers for zoom levels. The size of the image you see on screen depends on the monitor resolution for a start. What you see is not necessarily what I get.

With zoom steps of 25% I don't have fine contol when zooming out, and my point about the step being too small at high zoom levels is still valid. At 500% the next step would be only 525% instead of 625% — that's a big difference and would take 5 keystrokes instead of just one.

A geometric progression is definitely better. It matters not one iota whether the zoom level is in round numbers. All that matters is that you can zoom in or out easily, and quickly return to 100% (Control H), all of which one can do now — though I admit it could be improved. The maths may be tricky, but probably not beyond Irfan's ability to work out.

Zoom in/out with DrawPlus is synchronised to a great extent, but it does eventually go out of sync if you zoom in/out a long way. Probably rounding errors start to have an effect at some point. I can zoom out nine times to 14%, then back in again to 100%, but if I zoom out ten times to 11%, it goes out of sync, so that zooming in ten times then goes back to 110%

I can zoom in 17 times to 4,539% then back again to 100%, but if I zoom in once more to the maximum 5,000% then it goes out of sync and zooms out to 112%. Control 1, 2, 4, 8., will zoom to 100% 200% 400% 800%

There is no adjustment of the zoom increment, and no need for one either because it uses a geometric progression. One less option on the already cluttered options dialogue would be a bonus and might make coding this easier.

[Bh77]

Zoom in 4.10

Hi,
Here's some things about the latest zoom function:

1. First of all, there should be an option to choose between Proportional or Standard zoom. Some people like Standard, some like Proportional, and such an option would benefit everyone, even if this new zoom would be free of bugs...
   
   
2. Also, a hotkey should be available to dynamically switch between these two modes. E.g. Shift-Z to toggle Proportional zoom on/off.
   
   
3. Third, about the Proportional zoom, there is a way to always have the same values when zooming back and forth. Currently zooming in 5 times and out 5 times does not get back to the original 100% zoom.
   BUT, this could easily be avoided if the zoom values were precomputed. I mean, when the user chooses the zoom value, e.g. 15%, IV should calculate all the zoom values in the zoom range (from minimum (~5%?) to maximum (~4000%?) ).
   Then, every zoom action would simply step betweem these pre-established values, which will never change.
   
   As a side note, do these values really need to be integers?? I don't see why, and I think that having a 33,33% zoom would render more accurately than 33% as a "third-sized" image.
   
   
4. In the last version 4.10 (I did not test 4.0), zooming IN in fullscreen is progressively slower, even on small images. My harddisk starts working a lot, the RAM (1GB) fills up instantly when I zoom any little picture more than 1000%, or any larger picture more than 300%. [i have an Athlon64 3500+ 2.2GHz 1G ram]
   As for the real big pictures (6Mpixel) it's a disaster...
   
   Note that there is NO difference if I use Resampling in fullscreen or no resampling.
   
   Strangely, in normal view (windowed) the zoom works superfast even at 3000%, even on big pictures !!!
   So... what is so wrong with the fullscreen zoom? Is IV using the same algorithm in fullscreen and in window? It seems not...
   
   I think the solution would be
   (1) to use the same window-zoom technique for the fullscreen zoom, and
   (2) to resample (and keep in memory) only the displayed portion of the image, NOT the whole image.
   
   I guess i'm not the first to suggest this, but saying it again gives it more weight
   

Can't wait for 4.2......

[Bhikkhu Pesala]

Only number 4 is perhaps a bug, and a well known one at that. The rest are feature requests, so I have moved this thread to the feature request forum.

I don't know if there is much point in repeating feature requests that have already been made, so I have merged your post with the other thread on this topic.

[Bh77]

Heh I'm new to forums, still learning the basic rules, like read before you post...

You're right Bhikkhu, no point in repeating a bug notice, but I was also proposing a possible solution. I play the programmer myself at times, and know that any word of feedback could hint in the right direction.
So I think that pre-computing the proportional zoom values and stepping between them up and down, would do much better than calculating each time the new value, rounding it and losing precision, etc etc.

[Sam_Zen]

Another repeat

[MatthewW]

I fail to see why anyone needs to have round numbers for zoom levels.

It can be very useful when selecting areas. If I want to select a fixed size several times then having a rational zoom level makes it easy. That's not true if the zoom ratio is odd. For example, at a zoom of around 27% the size of a selection jumps in steps of 3 or 4 pixels, and if the zoom is slightly different for two images it may be impossible to get the same size each time. At 25% all sizes are multiples of 4. That may not matter to everyone, but it certainly matters to me.

A geometric progression is definitely better. It matters not one iota whether the zoom level is in round numbers. All that matters is that you can zoom in or out easily, and quickly return to 100% (Control H), all of which one can do now — though I admit it could be improved. The maths may be tricky, but probably not beyond Irfan's ability to work out.

For my purposes I need a zoom for which one level is precisely 100%. With the size of images I use Irfanview becomes painfully slow the moment the zoom gets even a fraction above 100% so when zooming in I need to be sure it'll land on 100%. A zoom that results in 101% is no good because the machine will freeze for a while. That's trivial to code: simply a matter of calculating back from 100% to find the required ratio instead of calculating forward from the current zoom. It also solves the problem of accumulated rounding errors: when zooming in and out the same ratios will be used every time.

[Bhikkhu Pesala]

If I want to select a fixed size several times then having a rational zoom level makes it easy.

Then use a custom selection (Shift C)

For my purposes I need a zoom for which one level is precisely 100%.

Then use Control H.

[MatthewW]

Control-H takes me to 100% straight away. I want a range of zoom levels, one of which is 100%, where that one is reached by a normal zoom process. I don't want to have to constantly check the current zoom level in order to make sure that on my next zoom I don't accidentally freeze the machine by going slightly over 100%. (Seriously, if I'm zooming in a zoom above 100% takes 30 to 40 times longer than one below or equal to 100%, so I need to be sure that I don't hit "+" and go over 100% by accident.)

Thanks for the tip about the custom selection.

[Bh77]

Seriously, if I'm zooming in a zoom above 100% takes 30 to 40 times longer than one below or equal to 100%, so I need to be sure that I don't hit "+" and go over 100% by accident.

Do you get this huge slowdown on both fullscreen-zoom and window-zoom?

I use 4.10 as well, but have NO speed problem whatsoever if I zoom in/out while not in fullscreen (!). The slowdown only happens in fullscreen for me.
That's why i suspect that IV is using two different algorithms for zooming, like two parallel procedures / functions or whatever.

My machine is an Athlon64 3.5GHz, on XP32 (yeah i know...) Pro SP2, with 1 GB ram. Good enough but not supertop.

[MatthewW]

Do you get this huge slowdown on both fullscreen-zoom and window-zoom?

I use 4.10 as well, but have NO speed problem whatsoever if I zoom in/out while not in fullscreen (!). The slowdown only happens in fullscreen for me.

It only happens when not in fullscreen for me, using 3.98. I rarely allow applications to use the entire screen so I hadn't noticed the difference. In fullscreen mode the zoom from 100% to 125% is just as fast as from 75% to 100%, but when not fullscreen it takes 10 to 20 seconds for 100% to 125% with medium-size images (around 3800 x 2400 pixels). I'd assumed it was a memory allocation issue when scaling the image to greater than 1:1, but that would apply all the time.

My machine is an Athlon64 3.5GHz, on XP32 (yeah i know...) Pro SP2, with 1 GB ram. Good enough but not supertop.

2GHz Athlon with 1.5GB.

[Bh77]

It only happens when not in fullscreen for me, using 3.98.

This is very interesting, as it never happened to me on any computer where I used IV pre-4.10. Including old machines like PIII with 800MHz and 512RAM.

when not fullscreen it takes 10 to 20 seconds for 100% to 125% with medium-size images (around 3800 x 2400 pixels).

I would call that rather large-size...

Anyway, have you double checked the settings for full and window zoom? Make sure you don't use any resampling technique.

ALso, have you tried the 4.10 and see if it's better or worse?

[MatthewW]

Anyway, have you double checked the settings for full and window zoom? Make sure you don't use any resampling technique.

Yes, it was resampling. Funny thing is, if I toggle the "View > Display options > Use resample" option then it affects the speed of zooming above 100% in the restored mode, but neither that nor "Options > Properties > Full screen > Use resample" has any effect on zooming when in fullscreen mode, which is always fast.

ALso, have you tried the 4.10 and see if it's better or worse?

4.10 behaves exactly the same as 3.98 in this respect; I'm using the latter because 4.10 has too many bugs right now.

[firesun]

The new Zoom function

Hi all, I'm a newbie here and I've read some posts about the new zoom function.

I'm an user from 3.x version and I really like the old zoom step function. Could you please give a checkbox control whether use the old zoom step or the new function?

Btw, I use irfanview to view the images in my work. In 3.x, I can view an image in 100%, 200%, 300% or another very easy by only click the + or - button. Now, as we know, I can not do this by same way and I must change the size of the image to view in correctly zoom.