Upsampling an image without changing the size

[AngrySalamander]

 

So this isnt for a project but I want to understand how this works for future printing jobs. In the attached screenshots I have an image thats I'm upsample from 72ppi to 300ppi while keeping the dimnesions the same. Lets say, for the sake of this question, this image was a tiny 6"x6."

My question has 3 parts:

1) How does this affect printing quality if scaled up to a standared print size (A3,A4...etc) after upscaling?/ How does this affect printing quality in general?

2) Is the 100% zoomed preview showing how my image will look if printed and if not does the prview window even matter?

3) Does illustrator show a good general view of how something will print with the "Overprint View" on?

Thanks y'all. If you need anymore screenshots/ info let me know

 

 

[Stephen_A_Marsh]

Question 1:

6” x 6" @ 72 ppi = 432 x 432 px… Resizing this to 300 ppi at 6” x 6" = 1800 x 1800 px

Resizing this to A4 would result in a resolution of around 150-215 ppi without resampling.

Results all depend on image content, scaling method, printing method and viewing distance/conditions.

Question 2:

100% in Photoshop maps 1:1, so 1 image pixel to 1 monitor pixel.

Again it depends on the output and the monitor, but you may find that 50% or 25% or another view may be closer in appearance/quality/sharpness compared to printed output.

Question 3:

Overprint Preview is specifically to show the result of overprinting, so if you had a yellow object over the top of a cyan object in normal view, you would just see yellow and cyan... But when you turn overprint preview on and if there is an overprint setting, then you would see green where the yellow and cyan overlap (similar to a blend mode like multiply or darken).

[Conrad_C]

1) In general, the more an image is upscaled, the higher the chance it will appear to fall apart. For example, 6 x 6 inches at 72 ppi upscaled to 6 x 6 inches at 100 or even 144 ppi might be somewhat passable, but the more you push it past that, the worse it’s going to look.

How soon the degradation is noticeable does depend on more factors. If the original was a high quality 72 ppi with decent contrast and sharpness and no defects (such as blocky JPEG artifacts), it might survive higher upscaling compaed to if the content was badly corrected, not properly sharpened (or maybe worse, oversharpened) and had compression artifacts.

Another very important factor is how you upscale. For example, the various Resample choices in Image  > Image Size resize images differently. Some are better for upscaling, some are better for downscaling, some are better for photographic content, and some are better for non-photographic artwork. But today, none of the Resample options in that dialog box can beat what is happening with new AI-powered upscalers, such as Enhance/Super Resolution (in Adobe Camera Raw) and Super Zoom (in Photoshop Neural Filters). Images that could not be upscaled very far with Image Size/Resample might be taken a little further with an AI upscaler that can do a better job of guessing and faking the missing details.

In short, if someone put a 6 x 6 inch 72 ppi image in front of me and said “Fit this to A4 at 300 ppi,” I would consider that potentially too extreme of an upscale for Image Size/Resample to do well, and instead first run it through a few AI upscalers and pick the best result out of those. (But first, I would ask if they have a full resolution original of the image that I could use instead, because that would have real details, instead of details that are educated guesses.)

2) 100% magnification only verifies what is happening at the pixel level, because it is the minimum magnification where you can see every pixel of the image. That is valuable and you should check the image that way, but it does not tell you everything about how an image will look in print. For one thing, the final printed image will not be seen at 100% magnification, people will see the print at View > Actual Size. Also, it will be printed using some kind of ink screening dot pattern (FM/stochastic, halftone dots, etc.) that the computer display is not simulating at all. And the display colors are not representing exactly how the colors will look in print, although you can simulate that somewhat closely by setting up and enabling soft-proofing in Photoshop on a display that’s color-calibrated, or at least profiled.

[D Fosse]

This is never going to work, put it out of your mind. It will look awful. Seriously.

The example you have here is deceptive, because the original is already over 5000 pixels long side, which is already big enough for anything. Upsampling that to 21 000 pixels is just beyond any realistic purpose.

But what you're proposing is 6 x 6 at 72 ppi, which is 432 x 432 pixels. That's not an image; that's a tiny thumbnail. There's no detail in 432 pixels.