Advanced question about printing and resolution?

[Tobasco]

I have a good understanding of PPI vs Pixel Dimensions vs Print Dimensions, as I work at a print shop.

However, something occurred to me that piqued my interest.

I'm kind of a perfectionist about printing sharpness. I use only the sharpest lenses when I plan on printing, and I like having the extra megapixels whenever possible (in scanning negs and in shooting digital).

My question is, what would produce a higher quality print when blowing up an image past what is "technically" possible with the resolution of the file?

For example. I have a DSLR that takes 12 megapixel images. At 300 DPI, a 4240x2824 (12MP) image will print at 14.1x9.4 inches. Say I wanted to blow it up to a 16x24 though. I know it's possible to just open it in Photoshop, crop it to 16x24 @ 300 DPI and print it, and I've even been very happy with the results I've gotten with that method, printing that size.

The other approach would be to lower the DPI. At 177 DPI, the print dimensions of a digital image that is 12MP go out to almost exactly 16x24 inches. So I guess I'm asking about the merits of having a print that is lower in pixel density but composed entirely of real, original pixels, and having a print the same size at a higher pixel density, but also a much higher ratio of interpolated pixels vs original pixels.

And, now that I think about it, is it better still to find a middle ground? For a 12MP image printing 16x24, at 177 DPI, I have 0% interpolated pixels. At 300 DPI, I have around 65% interpolated pixels if I did my math right (whoa!). So would somewhere in between, like maybe 225 DPI, give me an optimal percentage for an absolute highest-quality print?

[sanking]

My own preference would be to rezz up the file to at least 360 dpi at the print size. I am pretty sure you will give a sharper looking print this way than dropping the resolution to 177 dpi, especially if you view the print at close distance, say twelve to fifteen inches.

On the other hand if your viewing distance is two feet or more you should be able to get away with printing at 177 dpi at the print size.

Sandy King

[MumbleyJoe]

Well, whether YOU scale up the image to fit the printers needs (300dpi, or 360dpi, or whatever it prints at), or the printer (I guess its driver?) does the scaling for you. That conversion has to be made at some point, so trial and error may be the only way to decide what really works best.

When I had sent files off to Calypso for printing on their LightJet, they suggested NOT upsampling images because their conversion done on the lightjet hardware was typically 'better'. I can't say whether that was true or not, and I have no idea how different printers compare to one another either.

There are purpose-built applications, such as Genuine Fractals, that is specifically designed for up-scaling digital images. I have a friend that uses it routinely and loves it. I played with the demo and didn't feel all that impressed with it, but I had limited experience.

...don't know if that helps.

[Peter De Smidt]

What printer are you printing on? If it's an Epson, it will interpolate your file for you unless you give it a file at 720 dpi at the final image size. If it's an HP or Canon, I think that's 600 dpi. There are tons of ways to interpolate, stair stepped, overshot.... and how one does other editing, especially sharpening, will effect the result. The best way to test these things is to do some Googling, study some Photoshop methods, download some trial software, and do some comparisons.

[Kirk Gittings]

If it's an Epson, it will interpolate your file for you unless you give it a file at 720 dpi at the final image size.

Peter, Do we know this for sure finally? Is it written by Epson somewhere? I have heard so many opinions on this issue.

[Peter De Smidt]

It's what Roy Harrington says, and since he writes software (QTR) that replaces the printer driver, I expect he'd be in a good position to know.

[Jim Jones]

For an Epson 3800 this dummy resizes to 360 ppi and does any final sharpening and corrections so the printer merely has to accurately reproduce the file. Since this works, I haven't tried theoretial and mathematical approaches.

[Jeffrey Sipress]

If your printing at 16 x 20 and larger and you are not going to be looking at them close up (or pixel peeping) then you will likely see no difference between 360 dpi and 200 dpi prints. You work in the field, so you know that changing your file to 200 dpi will increase your print size by about a third. This should be no problem and show no deterioration if your viewing distance is at least 36".

[onnect17]

My two cents.
Do not use any sharpening. If you think you need it then something is wrong. If you need any correction do it in 32 bits. Convert to a wide color profile like ProPhoto. Avoid jpeg, use at least tiff 16. Get a real printing application with decent interpolation like QImage.

[Brian Ellis]

I send the file to the printer at whatever the dpi works out to be based on the file size and the print size except on the very rare occasions when I need to up-rez to get to 240 dpi. But most of the time I'd be down-rezing if I did anything and I never found a reason to do that, sending the file at whatever the dpi works out to be works fine for me. For a while I tried down-rezing to 360 or 300 and I never saw that it made any difference in how the print looked.

I've also seen far too many conflicting statements about "native resolution" of various Epson printers being 360 or 720 (or even something like 419 in one case) from too many people who should know what they're talking about to think anyone really knows what their native resolution is or exactly what they do when they receive a file with a different resolution. But if in fact my Epson 3800 does convert everything to 360 or 720 or some other predetermined number I suppose that would explain why just sending files at whatever the dpi works out to be does as well if not better than down-rezing to 360 or some other number.

I'm not suggesting that anyone who does it differently is wrong, just that I've been doing it my way for many years now and it seems to work fine.

[paulr]

I disagree with the suggestion to use no sharpening. I find sharpening to be critical in any kind of digital printing; sharpness gets lost both in the scanning process and in the raw mosaicing process, and needs to be restored. Print drivers also reduce sharpness slightly. I'd suggest a look at the most recent book in the Blatner / Frasier Real World Photoshop series for a tutorial on sharpening workflows. It's a subject by itself.

As to your original question, with many current inkjet print drivers, I see zero difference between interpolating in photoshop and just letting the driver do it. I'm still in the habit of resing up smaller files to 720 or 360 ppi, but can't say there's a good reason to do it.

My understanding is that things are very different with some other kinds of printers, like light jet.

In the end, the only way to know for sure it to experiment. It's easy; you don't have to make a 16x20 print. Just print small portions of one. You can print four print samples on a single 8x10 sheet for comparison.

[codex0]

Peter, Do we know this for sure finally? Is it written by Epson somewhere? I have heard so many opinions on this issue.

The tooltips and manual for my 3880 state that you should send files at 360dpi (native).

Checking the box for finest detail in the driver us it to 720dpi....
"Finest detail for sharper edges on vector-based data including text, graphics, and line art. (This setting does not affect photographs and is not recommended for large files)" (page 50 of the manual)

Also see here (http://people.csail.mit.edu/ericchan/dp/Epson3800/faq.html#native_res) (this page is about the 3800)

[Greg Miller]

My two cents.
Do not use any sharpening. If you think you need it then something is wrong. If you need any correction do it in 32 bits. Convert to a wide color profile like ProPhoto. Avoid jpeg, use at least tiff 16. Get a real printing application with decent interpolation like QImage.

Converting to a wide color profile like ProPhoto only helps if the color gamut of the image exceeds the range of a smaller gamut workspace. Take a foggy scene with a small gamut range. You would be fine with Adobe sRGB. Going to a wider color space will not help, and can actually hurt since both color spaces have the exact same number of total color values. And therefor the wider color space has to have bigger steps between the values to cover the larger range.

[Larry Gebhardt]

In my opinion the reason to resize to a consistent ppi is so any print sharpening will be consistent between your prints. If you sharpen first and send the image at 180dpi to the printer it will be resized to 360 or 720dpi by the printer. So any sharpening you do will also be doubled (your 1px radius will effectively be a 2px). While this will work just fine, it makes it hard to develop a sharpening system where you can look at the screen and know it will look good on the print.

So I always resize to 360ppi and sharpen right before printing. I sometimes resize to 720ppi if my scan or image has enough pixels and the fine detail matters. But then I need to experiment with the sharpening a bit.

The other reason I have heard to resize before printing is to take advantage of the better resize algorithms in Photoshop, vs what's in the print driver. Personally I have tested this, and can see no difference, but my experiment wasn't very well setup (just a few prints).

[Preston]

So I always resize to 360ppi and sharpen right before printing. I sometimes resize to 720ppi if my scan or image has enough pixels and the fine detail matters. But then I need to experiment with the sharpening a bit.

This is exactly the workflow I use. Works quite well.

--P

[James Hilton]

Peter, Do we know this for sure finally? Is it written by Epson somewhere? I have heard so many opinions on this issue.

On the 3880 "Finest Detail" mode is 720 dpi, and normal is 360 dpi. Print a grid of lines on gloss paper and you can verify this using a scanner. I have tried it and could print a grid of black lines at 720 dpi without any problems, the same goes for printing at 360 dpi with Finest Detail off.

Printing grids of lines at various resolutions and looking at the ugly results of driver scaling is a great advert for always sending at 360 dpi for photos!