Requested Change DPI w/ resize?

[DizzyEdge]

I'm looking for a way to not only change the DPI, but to retain the original print size while doing so.

For example, if I have a tiff that is 300 dpi and prints at 8.5"x11", I'd like the ability to change the dpi to 200, and have the pixel count reduce along with it so that the print size remains at 8.5x11.

I could do the math (200 dpi is 66.67% of 300 dpi so set image size to 67%), however the input files might be variable dpi, whereas I wish all the output to be 200 so if one file is 300 dpi, it will need 67% resize, if another is 400 dpi it will need 50% resize, etc

Is this possible at all?

Thanks!
-Chris

[midora]

Open Resize/Resample dialog.
Select "Set new size" .
Select units = "inches"
Now set DPI value on the bottom.

But you have to do it in this order.

[DizzyEdge]

I'm sorry I missed an important piece of information, I need to do this as a batch process, so the images being processed will be variable page sizes, but all need to be reduced to 200 dpi, while retaining their print page size.

Thanks

[Laurent]

Hi DizzyEdge,

The answer to your question is given in IrfanView help file (Overview | Command Line Options): /dpi=(x,y) - change DPI values.

Laurent

[midora]

Laurent: This just changes the DPI values of the image but it does not resize the image so the print size will change.

I don't think you can do what he asked for only from the resize dialog not from batch dialog and not from commandline. Would be nice if Irfanview would allow this.

[Bhikkhu Pesala]

Use the thumbnail view to sort the folder by image width, then start batch operations with selected files. Then you can set the image width in inches while changing the dpi. You may have to do several batch operations, but at least you won't have to do the images one at a time.

[midora]

Still it would be easier doing it w/o thinking ;-) Especially because the functionality is available in the direct operation.

I guess "sort by image width" uses pixels not inches/cm, which forces you to be more careful....

[Laurent]

Hi midora,

I believe the solution is to be able to set something like:
/dpi=(50p,50p) (with p for percent)
as we already can do with resize:
/resize=(50p,50p)

Should I post this to feature request?

Laurent

[DizzyEdge]

One thing I noticed is if you set DPI, the DPI changes, but the pixel size remains the same. If you also check "Set new size as percetage of original", and set it to 100% x 100%, that causes no change, as the 100% seems to apply to pixel size, which isn't being changed anyway when you modify DPI.

So a good feature change would be for the "Set new size as percentage of original" to have a radio button that lets you choose pixels/print size. Then if you set a DPI, and choose page size and 100%, it would change the DPI, and resize the image so that the inch x inch size is the same as the original was.

A less flexible alternate solution would be to have a checkbox next to the "Set DPI value" that reads "retain print size"

[DizzyEdge]

One thing I'll mention, is you can do what I'm asking by figuring out what percentage of your old DPI your new DPI, and putting that percentage in the "Set new size as percentage of original" For example 200 is 67% of 300, so if you have 300 dpi pages, and wish to resize to 200 dpi, you can also put 67% x 67% in the "Set new size as percentage of original" and it works. The only caveat is you have to be sure all incoming files are all 300 dpi, and you have to do a little bit of math. Having the software calculate the % on a page by page basis would be a bit more elegant, and would handle input pages of mixed dpi.

[Sam_Zen]

This is quite a math problem.
You want an image with DPI-values a, pixel-values b and printsize-values c
Changing of a and/or b makes printsize-values d
Two problems here:
~ c of the original is then lost, it is not saved in some way, so can't be recalled for a final process.
~ d is not able to influence a and/or b directly, because it's a result, not a variable.
I checked the print-dialog, being a proper place for this I think.
I noticed that this is quite poorly supported in IV. It only has a default start, nothing's saved.

[midora]

Hi midora,
I believe the solution is to be able to set something like:
/dpi=(50p,50p) (with p for percent)
as we already can do with resize:
/resize=(50p,50p)
Should I post this to feature request?
Laurent

I would prefer to keep the meaning of the p modifier and to propose a more general solution.

As you know the following formula is valid for an image:
dots = dpi * inches
(horizontal and vertical may be independent).

Based on this formula there are six possibilities

dots | dpi | inches | command | modifiers
----------+-----------+-------------+----------------+-----------
set | keep | calculate | /resise=(h,v) |
set | calculate | keep | /resize=(h,v) | i or c
keep | set | calculate | /dpi=(h,v) |
calculate | set | keep | /dpi=(h,v) | i or c
keep | calculate | set | /rescale=(h,v) |
calculate | keep | set | /rescale=(h,v) | i or c

Number one and three are available in the moment. I propose to add one additional command and a modifier (i or c) which can be used with all three commands (/dpi, /resize, /rescale).

The modifier i or c (inch or cm) should be appended to the value like the modifier p (percentage). It should be possible to use p and i or c together.

Using these three commands you know that
/resize sets the dots
/dpi sets the dpi value
/rescale sets the inches (virtually as you know)
one of the other two values will be kept and the other one calculated.

And as a example for what the thread started with you have the to write the following on the commandline:

/dpi=(200i,200i)

Means change the dpi and keep the inches at the same time.

[Sam_Zen]

Quite an elegant solution to this, midora.

[Laurent]

Hi midora,

I spent a long timpe trying to understand and become familiar with your six possibilities. It is difficult. I believe the reason is the namings of some options and the mixings of elements concerning pixels numbers and the modifiers i or c. For example /dpi=(200i,200i) is misleading to me because it suggest that only DPI will be altered, but pixel number will be altered too.

Suggestion for renaming:
1. /resize=(h,v)
2. /resize=(h,v) /keepprintsize # adjust dpi value
3. /dpi=(h,v) /[percm|perin (default)]
4. /dpi=(h,v) /[percm|perin (default)] /keepprintsize # adjust pixel number
5. ??? /rescale=(h,v)
6. ??? /rescale=(h,v) | i or c

5 and 6: not a good name and parameters and modifiers not selfspeaking enough.

With the choice [percm|perin], the naming /dpi is strange. -> /resolution?


Laurent

[midora]

I agree this i as modifier is not quite good. To use an additional option instead is better.
At the end if Irfan changes anything there then it would be good to implement a closed solution which is from the naming compatible with the current one.
Do you think that we should find a solution which can be agreed by all people discussing here? Or should we just provide the current state as a couple of ideas what to do in this area?