Why would you ever want to upsample a photo?

[adamh88]

Hello everyone,

Please excuse me for being naive but I can't seem to get a firm grasp on upsampling. Say you have a 5 x 10 photo at 200 PPI and you are sending it to an offset printer so you upsample it to 300 PPI. Is the printed photo really going to look better upsampled? Does it depend on the photo?

[D Fosse]

adamh88  wrote

Say you have a 5 x 10 photo at 200 PPI and you are sending it to an offset printer so you upsample it to 300 PPI. Is the printed photo really going to look better upsampled?

No, you're absolutely right, it will not look better. Usually much worse because of artifacts introduced by the resampling.

Printing at 200ppi will usually turn out just fine. Contrary to what people believe, it will not be noticeably less sharp. It just means you may be able to make out individual pixels (which by definition you cannot at 300).

The line screen is still 150 lpi. That's the effective resolution.

[D Fosse]

That said, I always try to keep 300 for book print and for my own images that's obviously not a problem. But if I receive a small image that has to be reproduced at less than 300, I just let it go as is.

And of course, 300 is for books and magazines. Anything to be seen from farther away requires less accordingly.

[adamh88]

Thanks for the reply, I really appreciate it. I'm pretty sure I understand the concept of upsampling but I honestly can't think of a useful scenario. It just seems like upsampling isn't going to increase the quality. Do you know of any times it would actually be beneficial to do?

[D Fosse]

To be honest, no

I'm sure someone will disagree, but I always find the resampling artifacts tipping the balance the other way.

[davescm]

I up-sample in two scenarios (only the first may apply in the circumstances you describe)

1. Where an increase in size without upsampling will lead to visible pixels at the intended viewing distance.

2. Where the image may be scaled later in the process and I want to control that scaling within Photoshop. An example would be my Epson inkjet where the driver will scale to 360ppi if not sent an image at that resolution. For photographs it is not discernible but for some graphic elements it is and in Photoshop I can choose the scaling algorithm.

Dave

[D Fosse]

davescm  wrote

Epson inkjet where the driver will scale to 360ppi if not sent an image at that resolution

- but will it scale pixels per inch? Will it not just print, say 240 pixels per inch at 360 dots per inch (and stochastic dots at that)?

Not saying you're wrong, just trying to get this straight...

[davescm]

Hi Dag

A while back, I tried some sample images created at 362ppi 361ppi, 360ppi 359 ppi 358 ppi etc (fine black and white circles which would show any "unpleasantness"). All but 360ppi showed artifacts introduced in the print driver. It was borne out by some testing done by Eric Chan, of camera raw fame, who at the time ran the same printer.

Note : This was on my Epson 3800 - other print drivers may differ.

Note 2: As I said in the post earlier this was visible on fine graphical elements. I have no doubt the same scaling was going on for photographs, as both were sent to the print driver as flat pixel images, but on photographs it was not visible (to my eyes anyway),

Dave

[D Fosse]

OK

[adamh88]

Hi davescm,

Thanks for your input. I wanted to discuss this point a bit more if you don't mind:

1. Where an increase in size without upsampling will lead to visible pixels at the intended viewing distance.

This is all hypothetical and not something I would hopefully run into often. So lets say I get a 5 x 10 photo from a client at 200 PPI and it needs to print at a larger size... 7 x 11 or something along those lines....Obviously you're going to lose quality by enlarging the photo but from what I've seen--if you upsample and increase the size...it will look worse than if you just increased the physical size. Thus...I am confused as to what upsampling accomplishes. Am I missing something here?

[davescm]

Hi

At that increase I would just stick with the larger pixels. I was thinking of larger increases where it becomes a balance between the visibility of blocky pixels, if you don't up-sample, versus a smoother transition but with the artifacts that are inevitably introduced with up-sampling.

If in doubt look at both then let your eyes decide based on your image and your degree of enlargement.

Dave

[mglush]

Hi!

While I agree that you want to use an image at 300 ppi at size, there are times when I didn't have an image (that I HAD to use) with enough resolution. So, up-samping was a necessity. In working as a graphic designer, I am often called upon to resize and upsize images for large format printing of banners, signs and posters.

I used a formula that I learned many years ago to increase the percentage in the Image size dialog box to 150% (sometimes doing it a number of times) until I got the size in the ballpark and then resize it from there. I got really good results.

Your clients don't always hand you off the best images, and expect you to work miracles. Sometimes that is real life and you have to do the best with what you are given. Have a resampling option in your arsenal of tools can be a real benefit.

Michelle

[Trevor.Dennis]

You at least retain control of the process if you handle the upsample.  Yes it depends on the particular image, and there are numerous means to do the upsample.  To my mind, the recently introduced Preserve Details 2 is a clear improvement on the original version, and the best process to increase pixel size currently available.

[adamh88]

Hi Tevor.Dennis,

Thanks for the reply and thanks for mentioning Preserve Details 2. I had not previously tried this option out. I played around with it a bit and it did a good job of reducing some pixelation/noise--although it did remove some detail. I could see it being useful in certain situations.