New Zoom option in 4.20

[Sjef]

Properties»Viewing»Zoom calculation - dialog

Zoom step: 100% (as an example)

Relative calculation: working, every next zoom is 100% (works fine for me)
Absolute step: working, but I can't get to the logics about this steps. They seems to get smaller (so Relative) by every next zoom.
Fixed values: working, but ‘Zoom step’ percentage doesn't work and appear to be fixed at 10%

To my logic the radiobuttons Relative and Absolute step should be exchanged. Am I wrong about this and what could be the benefit of this three zoom options?

[Skippybox]

Re: New Zoom options in 4.20

Hi Sjef!

The new zoom options are actually quite straightforward. You just need to experiment with them. In IrfanView Help (F1), under Contents>Options Menu>Properties,Viewing it explains:

"Zoom step sets the factor/value for Zoom In and Zoom Out. The default is 10% increase or decrease each time you zoom the image. Type a number in the box to change this amount. Zoom calculation sets the method how the zoom values are calculated. Relative: the next zoom value will be calculated using the current/previous zoom value and zoom step; Absolute: the next value will add/subtract the absolute zoom step to the current value; Fixed: the zoom values are taken from a fixed table of common/popular zoom values."

To my logic the radiobuttons Relative and Absolute step should be exchanged. Am I wrong about this and what could be the benefit of this three zoom options?

I think they make sense the way they are if you understand them, but perhaps some tweaking could be made. I mean, fixed and absolute sound the same!

The three zoom options are actually quite simple, but this is an in-depth observation of them:

Zoom level is a measure expressed as a percentage, of either dimension (height or width) of an image, relative its original true size. Thus, if the height or width of an image was half of what it truly was, the zoom level would be 50%. If you square the zoom level you obtain the zoom area of the image compared to the original area. In our example, the 50% zoomed image would only be 25% as large (by area) as the true size [0.5*0.5=0.25.].

Because zoom is expressed as a percentage, and the nature of percentages to be relative, a certain ambiguity exists in this discussion. Unless we are referring to the relative zoom calculation, when we are talking about how the zoom level changes, we will be using an additive/subtractive sense, rather than a multiplicative/divisional sense. In order to satisfy this, I will use the term adjusted zoom step, which will represent the change in zoom level between the current zoom level and the new zoom level. To obtain the new zoom level, simply add the value of the adjusted zoom step to the the current zoom.

During this discussion I will try to use notation to clarify. Let:

any zoom level=z
zoom step=s
adjusted zoom step=a

Relative step is useful because it allows the dimensions of an image to change the same amount on each zoom without respect to the original size of the image. That is, no matter what zoom level your at presently, the dimensions will increase by the zoom step multiplied by the current zoom level [IN:a=z*s, so z+a OR z+z*s=z(1+s) OUT:a=z-z/(1+s), so z-a OR z-(z-z/(1+s))=z/(1+s)]. This is what makes it relative. Relative zooming is good if you aren't interested in zooming based on the original size, but instead based on the size you are zoomed at currently (i.e. you always want one of the dimensions to be consistently 50% larger than before). One example of use is if your image's pixels are multiples of the screens pixels and you would like to examine square ranges of resampled pixels (1, 4, 9, etc.).

Absolute step is useful because it allows the dimensions of an image to change the same amount on each zoom with respect to the original size of the image. That is, no matter what zoom level your at, the dimensions will increase by the zoom step multiplied by 100% (original size), which is why it is absolute [IN:a=1*s=s, so z+a OR just z+s OUT:z-a]. The absolute zoom does not require a calculation, as the adjusted zoom step is simply equal to the zoom step. This is the traditional zoom option used in versions of IrfanView previous to 4.1. Absolute zooming is useful if you are interested in zooming based on the original size (i.e. you want one of the dimensions to increase to increase always by 10% of the original image.) This setting is very useful as the zoom is predictable and can be used to step to any zoom level needed.

Fixed values ignores the zoom step altogether and instead moves to the nearest popular zoom level. This allows for progressively quick zooming through the most needed zoom levels, both small and large.

All three zooms can be used together in a sequence for some type of advanced zooming scenario, or they can be used alone depending on what types of tasks you do most often.

Relative Zoom Bug

Both relative and absolute zoom are relative in another sense. They both are dependent on where you start zooming. Thus, its important to know where to begin. This is especially important in relative zoom because of its nature, in order to zoom back to where you started from. With version 4.2 correcting the relative zoom bug, the functionality of relative zooming has been unfortunately diminished. Because the program has to figure out where you were, it uses the wrong calculation for relative zooming out. It uses the current and previous zoom levels to determine how to get back, but this requires that zooming out divide by (1+s) instead of version 4.1's correct multiplying by (1-s). We know these are not equivalent, because s would need to be zero. As an example, if z=100 and s=10, zooming in would multiply by 1.1 and zooming out would divide by 1.1. However, the reciprocal of 1.1 is approximately 0.901, which is not the expected 0.9 necessary for relative zooming out, but it does work to undo each zoom in (90.1%*110%=100%). Unfortunately, to accomplish the correct relative zooming would require knowing where you started from and more calculation. Also it would be tricky trying to change starting points as this feature would depend on it immensely.

I think using Sjef's 100% example to start experimenting might be confusing comparing the three choices. But, I can explain.

Zoom Step: 100% Starting Zoom Level: 100%

Relative step:
In: 100%, 200%, 400%, 800% ... Out: 800%, 400%, 200%, 100% ...
Out: 100%, 50%, 25%, 13% ... In: 13%, 25%, 50 %, 100% ...

It's relative, so zooming in you are adding 100% of the current zoom to the current zoom or doubling it (z+a=z+1z=2z). Zoom bug fixed, so zooming back out you are dividing by 2 to arrive back at original starting point.

Absolute step:
In: 100%, 200%, 300%, 400% ... Out: 400%, 300%, 200%, 100% ...
Out: 100%, 50%, 25%, 13% ... In: 13%, 113%, 213%, 313% ...

It's absolute, so zooming in you are adding 100% to the current zoom (z+s=z+1). Zooming back out you are subtracting 100% from the current zoom (z-s=z-1). You can't have 0%, so below 100% the current zoom is divided by 2. If this happens though you run into a problem. This could be the start of another zoom bug! When you try to zoom back up, you add 100% to these relative zooms and can't return to your original starting point! The algorithm forgets to undo these relative zooms!

Fixed values:
In: 100%, 115%, 132%, 150%, 174%, 200% ... Out: 200%, 174%, 150%, 132%, 115%, 100% ...
Out: 100%, 87%, 76%, 66%, 57%, 50% ... In: 50%, 57%, 66%, 76%, 87%, 100% ...

The 100% step is ignored because the zoom is fixed; it's determined by a table of common values.

Here's another example:

Zoom Step: 100% Starting Zoom Level: 79%

Relative step:
In: 79%, 158%, 316%, 632% ... Out:632%, 316%, 158%, 79% ...
Out: 79%, 40%, 20%, 10% ... In:10%, 20%, 40%, 79% ...

Absolute step:
In: 79%, 179%, 279%, 379% ... Out:379%, 279%, 179%, 79% ...
Out: 79%, 40%, 20%, 10% ... In:10%, 110%, 210%, 310% ...

Fixed values:
In: 79%, 87%, 100%, 115%, 132%, 150% ... Out:150%, 132%, 115%, 100%, 87%, 79% ...
Out: 79%, 76%, 66%, 57%, 50% ... In: 50%, 57%, 66%, 76%, 79% ...

A better example:

Zoom Step: 25% Starting Zoom Level: 50%

Relative step:
In: 50%, 63%, 78%, 98% ... Out: 98%, 78%, 63%, 50% ...
Out: 50%, 40%, 32%, 26% ... In: 26%, 32%, 40%, 50% ...

It's relative, so zooming in you are adding 25% of the current zoom to the current zoom or multiplying by 1.25 (z+a=z+ 0.25z=1.25z). Zoom bug fixed, so zooming back out you are dividing by 1.25 to arrive back at original starting point.

Absolute step:
In: 50%, 75%, 100%, 125% ... Out: 125%, 100%, 75%, 50% ...
Out: 50%, 25%, 20%, 16% ... In: 16%, 41%, 66%, 91% ...

It's absolute, so zooming in you are adding 25% to the current zoom (z+s=z+0.25). Zooming back out you are subtracting 25% from the current zoom (z-s=z-0.25). You can't have 0%, so below 50% the current zoom is divided by 1.25.

Fixed values:
In: 50%, 57%, 66%, 76%, 87%, 100% ... Out: 100%, 87%, 76%, 66%, 57%, 50% ...
Out: 50%, 43%, 38%, 33%, 28%, 25% ... In: 25%, 28%, 33%, 38%, 43%, 50% ...

The 25% step is ignored because the zoom is fixed; it's determined by a table of common values.

• In summary, other than the new bug, I think these zoom options are the best thus far and seem to each have a purpose. They allow for quite a bit of customization and can be changed rather quickly. I usually use the fixed value zoom. However, I don't quite get what some of the values are for or why some are unusual (76%, not 75%?). Still, it would be great to directly enter a zoom percentage!

[j7n]

Now that "Fixed" works well enough I haven't really used "Absolute 25%" anymore. In my opinion under this mode the old zoom should be preserved as-is, without further adjustment as you approach 0%. If one needs proportional zoom, one of the other 2 modes will be satisfactory.

76% really is an odd value, but – thank god – we can have exactly 25%, 50% and 200%. Viewing at 75% doesn't really look any good to complain that this step is not available.

[Sjef]

Zoom options

Obviously I was too impatient with the Help file, because I couldn't find the explanation about the three new zoom options (untill now).
Thanks for your clear and very extensive explanation, Skippybox

In summary, other than the new bug, I think these zoom options are the best thus far and seem to each have a purpose. They allow for quite a bit of customization and can be changed rather quickly. I usually use the fixed value zoom. However, I don't quite get what some of the values are for or why some are unusual (76%, not 75%?). Still, it would be great to directly enter a zoom percentage!

I agree. Not all viewers have zoom options allowing a percentage or a ratio. But for me it should have been enough to have the one simple zoom option from earlier versions. I still don't see the benefit of having this three posibilities, although you made it clear how they work.
In View»Display options (Window mode) one can check the Resample option for a nicer (but slower) view, even at 75%

[Sam_Zen]

Still haven't got the time to test this new option thoroughly.
But due to the extensive contribution by Skippybox, I think this thread could be a candidate for the tech-doc department.

[Skippybox]

Thank-you!

Thanks everyone for the complements. I just felt compelled to give back to this wonderful product and community! I am thinking of revising my original post though, to improve it further.

[Skippybox]

Revised!

Just finished revising my original post (#2). Hope you like it and find it more understandable. Tell me what you think.

Also:

Note, there is a workaround for directly entering a zoom level fullscreen, under Properties>Full screen>Set display multiplier (%), but you have to enter your percentage twice for a balanced image. It is important to understand that this is a factor, so it will multiply by any zoom that you're at. If you want the exact zoom you entered, either change the full screen display mode to Show images/movies with the original size or press 1 in fullscreen mode for 100% zoom.

As a backup, use the Properties>Full screen>Full screen only: >Show text option and use the code $Z to verify the zoom level!

[Skippybox]

Technical Documents Department

...due to the extensive contribution by Skippybox, I think this thread could be a candidate for the tech-doc department.

How would that work?

[greentree]

Skippybox, WOW! Your details are awesome! I wish I had read this extensively before creating my thread (which is redundant because of your post).

I was given the solution to what I wanted, but now I understand *why* the various zoom options function the way they do.

THANKEES!! Two thumbs way up!

[Mij]

It seems to me that the wording in the Help file could be improved. Not easy. This is my attempt;

Zoom Calculation sets one of three different methods by which the image zoom ratio is increased or decreased for each zoom step in or out. For the first two methods the size of the step can be varied by adjusting the Zoom Step setting (default 10%).
Relative (variable logarithmic): The zoom ratio changes by a percentage of its current value for each step.
Absolute (variable linear): The zoom ratio changes by a constant percentage for each step.
Fixed values (fifth octave logarithmic): The zoom ratio steps to fixed values contained in a table. Common fixed values such as 50% (1:2) and 100% (1:1) are included.

[Skippybox]

greentree,

Thanks so much!

Mij,

Not easy is right. Very difficult to explain them in a simple yet illustrative way. Yours is good because it explains things such as why the fixed values are not always typical. Whether or not others know what you mean by that, is the question. Speaking of which, did you notice 12.5% is missing?

[Mij]

I am not surprised that the help file on this subject confuses newcomers, but was concerned that it manages to confuse 2 moderators who have lots of experience of IrfanView.
While your explanation is great, Skippybox, you cannot have half a page of explanation in the help file which is why I started tinkering with the wording we actually have.
I think that the start is most important. Do you find the first 2 lines any less confusing?
Actually I think that zoom is pretty confusing before you even start reading because it is expressed in pixels on the Title bar and as a percentage on the Status bar. I used the term Zoom ratio throughout to indicate that I was talking about the figure on the Status bar. Does that succeed?

I also thought it important to point out that the Zoom Step setting related to the Relative and Absolute methods and not to Fixed Values.

I knew that terms like Logarithmic, Linear and Fifth Octave in the sub-titles of the three methods would be unfamiliar to many readers but thought they might be helpful to those who do know them. They are much better defined than words like Relative, Absolute and Fixed. Not the place to define them here though.

I reckon that Relative and Fixed value are pretty hard to accurately describe any other way. In Relative the Zoom ratio is actually multiplied by 1.1 for the default 10% step when increasing and divided by 1.1 on the way down.

In Fixed Value the multiplier is 1.1487 (the fifth root of 2). That gives integer values every fifth step (25%, 50%, 100%, 200%, etc.) but steps in between have to be rounded to integers. In fact 9% and 11% are the nearest true values on the scale not 10%, 13 (for 12.5) is missing and 21, 28 and 43 should have been rounded up not down. 150 should be 152, 260 should be 264, 300 should be 303... so there are already a number of adjustments in the table.

Which is all quite interesting but does not help to clarify it to the already confused.

[Skippybox]

I am not surprised that the help file on this subject confuses newcomers, but was concerned that it manages to confuse 2 moderators who have lots of experience of IrfanView.

It is disconcerting. There are far more things to be confused about, instead of this.

While your explanation is great, Skippybox, you cannot have half a page of explanation in the help file which is why I started tinkering with the wording we actually have.

I realize this, but that's why it's on the forum. If the Help file was sufficient all of the time, this support forum would be of much lesser value.

I think that the start is most important. Do you find the first 2 lines any less confusing?
Actually I think that zoom is pretty confusing before you even start reading because it is expressed in pixels on the Title bar and as a percentage on the Status bar. I used the term Zoom ratio throughout to indicate that I was talking about the figure on the Status bar. Does that succeed?

I think I'm the worst person to ask, since I already understand the whole topic quite well. While I can relate to the feeling of confusion, I really don't know what aspect others find as being confusing. Obviously, we each have a different level of confusion and capacity for comprehension. It is better to ask them. Things are much more confusing in the beginning.

I think the pixel readout is a non-issue at least for this topic. However, I'm sure it confuses them in other ways.

I also thought it important to point out that the Zoom Step setting related to the Relative and Absolute methods and not to Fixed Values.

Yes, that is highly important.

I knew that terms like Logarithmic, Linear and Fifth Octave in the sub-titles of the three methods would be unfamiliar to many readers but thought they might be helpful to those who do know them. They are much better defined than words like Relative, Absolute and Fixed. Not the place to define them here though.

That is true. I've never come across the term octave in this context, but you, being in the electronics industry, it probably makes sense for you to use it. I probably know it by a different term.

In Fixed Value the multiplier is 1.1487 (the fifth root of 2). That gives integer values every fifth step (25%, 50%, 100%, 200%, etc.) but steps in between have to be rounded to integers. In fact 9% and 11% are the nearest true values on the scale not 10%, 13 (for 12.5) is missing and 21, 28 and 43 should have been rounded up not down. 150 should be 152, 260 should be 264, 300 should be 303... so there are already a number of adjustments in the table.

This is what has me confused. Why adjust it in some instances, but not others? Why the inconsistency? I suspect 10% might be a limit, but the other cases are strange, given this is a table.

Which is all quite interesting but does not help to clarify it to the already confused.

Sometimes people have to take it upon themselves to learn. We can only do so much.

[Mij]

.... I've never come across the term octave in this context, but you, being in the electronics industry, it probably makes sense for you to use it. I probably know it by a different term.
......This is what has me confused. Why adjust it in some instances, but not others? Why the inconsistency? I suspect 10% might be a limit, but the other cases are strange, given this is a table.

It is more acoustics (or music) than electronics but you do find it elsewhere when you want numbers that are harmonically related. I support your view though. There is no need to use it here. I would choose a set of values like 5, 10, 15, 20, 25, 30, 40, 50, 60, 80, 100, 200, 400, 600, 800, 1000

[Skippybox]

I'm not sure what would be a good table, but I would like to see enhanced zoom accuracy to 1-2 decimal places. Rounding to the nearest 1% makes it very hard to use ratios, which leads to compounding errors. Typing in the ratio would also be appreciated alternative.