Question about DPI and resizing

[rsn]

Hey guys, quick dummy question...I'm a photographer but I normally display my work online. I have recently thought about selling prints, and in the process have run into some confusion over resolution (which is ridiculous because I should know this very well already, but sadly need a little clarification).

If I increase the resolution but do NOT increase the dimensions, it shrinks the print size (ex - bump resolution from 180 to 300 dpi but adjust pixel dimensions back to 100% resulting in the print size losing about 4x4 inches). I assume this is a very stupid thing to do, right? Because the print size of the pictures would end up quite small and rather than preserving or enhancing the quality, it would ruin it if someone wanted a larger print.

I never enlarge images by pixel size alone due to obvious quality loss but if I increased the dimensions dramatically to match the DPI (for instance, set it to the highest resolution possible and accept whatever automatic increase in pixel dimensions that brings), would that be a mess or would it balance out and look all right?

Or am I just better off leaving the resolution and dimensions alone and assuming it'll look good printed in its natural state? Because the quality is very nice on screen but my concern is how it will as a photo print or on canvas of varying sizes (within reason; obviously I would not suggest printing a 12x9 image at 60" but a good quality image should be able to print at slightly larger sizes without noticeable loss). Any thoughts?

[LeviFiction]

So Pixel dimensions, for the most part are the "real" photograph on the computer. You delete any, you can't get them back. You try to add more it guesstimates and creates horribly globbly looking things with decreased contrast.

DPI (PPI) or Resolution is how many pixels (dots of color) will be placed within a physical inch once printed out.

Print Dimensions is the result of Pixels/DPI.

If I have 3000 pixels wide by 3000 pixels high, and a resolution of 300 DPI the resulting Print Dimensions will be 10" x 10"

=================

Because of this relationship you have do one of two things when making a larger print. You either have to increase the pixels, or decrease the resolution.

Resolution should be based on the viewing distance from the audience if possible. If the average viewer is going to be looking at the image at a distance of 2 feet you would use a DPI of 250-300 for a good quality. 3-feet maybe 200dpi. 5 feet 120-250 dpi and so on. A billboard for instance can have a dpi of 25 pixels per inch and have the exact same number of pixels that you're working with right now. It only looks so good because you're seeing it from so far away.

There will be those who disagree from experience and awesome. Better listen to them than me but this is my understanding from reading. In fact do a lot of research on recommended resolutions for sizes and viewing distances to get a real good idea of what you're aiming for.

So really consider your audience here before determining you need 300dpi resolution. And understand you have wiggle room it doesn't have to be an exact 300dpi.

If you intend traditional held in the hand distance for your images so a dpi of 250-300 but just don't have the pixels necessary you will have consider upscaling the photo. Now upscaling is generally frowned upon and for good reason. But if you can balance decreasing the resolution, and increasing the pixels the damage can be kept small. Still not recommended if you can avoid it. Because if the quality isn't there, it just isn't there. You can't force it out. You can disguise it, but you can't force it.

So get as close to the lower DPI level that you can without compromising quality, then start increasing the pixels slightly.

Otherwise go with a smaller sized print.

Eventually you'll get a camera with more pixels and you can start being freer with your imagery whereas right now you're struggling to make the pixels fit.

[hartpaul]

There was a good explanation with images by Lisa Snider King about "The Reality of Resizing images in Photoshop" in layers magazine some time back.
The original article has had the images removes but there is still a black and white pdf available (Google search that including the quotes). It looks like the person that has made that available printed out the original as black and white , and then scanned it and converted to a pdf.

http://www.unmc.edu/biochemistry/docs/R ... toshop.pdf

Another version is available here :
http://www.tfwm.com/0407_graphicsecrets
but without the images.
It is explained in terms of photoshop but has universal usage for most graphics programs.
Bit more searching and managed to locate full version here:
http://www.webdesign.org/photoshop/arti ... z1DcKxUbjE

[brucet]

Here's a non expert response! No facts or data to support my opinion just experience.

I shoot with a D7000. Use ASP and PSPx6 for all my work with 16bit tiffs.

I start and stay with 16bit tiffs and leave everything at 300ppi. Don't make any changes in PSPx6 even though I do do small resizes.
Print mostly A4. But often have printed by a pro lab 40"x30", approx, canvases.
My A4's are printed with QImage at 720ppi equivalent on an Epson 1410. QImage is an excellent print program. QImage will take control and give you the best outcome for any given file.

Now the point of my comment.

My eyes see a final product/print that is hard to fault.
Provided you maintain the 300ppi/dpi 'standard' then you should always be ok. If you want to use a lower ppi/dpi then make a copy and down size it. Never down size your original.
I've read hundreds of posts about what you 'should' and 'shouldn't' do. I have no idea if what I'm doing is 'correct'. But I do know what I'm doing is satisfying galleries and museums.

I was paranoid about losing details. Do some test prints and make your own decisions.
The maths will only confuse you. And test print will give you the answer you are after.

regards

[Forriner]

I don't want to hijack this thread but I'm curious.
I have no problem understanding DPI / PPI. But I have always wondered how important the DPI value encoded into a file really is to the printer these days.
When I take my files to the printer, I order certain sizes. For example I can get one file printed at 10cm × 15cm and 20cm × 30cm. So the DPI resolution stated in the file means nothing to the guy and his process. Unless I want a print size that brings the actual print DPI down so low that he'd be out of business in a week because of lack of quality, then he warns me about it.
If I make an album the files fill the frames in the template.
Are there situations that the printer actually uses the DPI setting in the file to determine the print size? As in: If you want your 3000×4000 pixel file to print a 3 × 4 inch card, you're going to have to get the DPI value 1000 into the file. Or resample to 900 × 1200 and get 300 into the DPI field?
As I said, I'm just curious, but I've never encountered a situation where the DPI in the file is important, a deal breaker, while the question of changing DPI in the file comes up regularly. Is that a waste of time?

[rsn]

Thank you guys so much! This has all been very helpful. The problem for me is that so much of what I do is, as I said, intended for digital display and only recently have I realized that I have a lot of nature and landscape shots that should look great as framed and canvas prints. I just want to make sure I'm approaching it in the right way, since there's a big difference between digital and physical display. So this is a great start and I'll look through the links provided and do some trial and error from there

[brucet]

I'll get shot in the backside here by the technical experts but!
But the way I see it is as long as you keep your files and printing at their highest level then you should get great results. I would only ever consider reducing ppi/dpi for web based sites which impose limits. After all why else would you want to degrade what you have worked so hard for? (A file at 300ppi and printed at the highest dpi onto a 6x4 doesn't hurt anyone and gives a great result. I don't understand reducing any criteria when the printer will, if set correctly, print the highest dpi it can. Even on a 6x4).

Software and hardware developers have worked hard to produce products to give excellent results. Leave the technical stuff to them. You don't have to understand it. Nice if you do but it's not essential to understand the maths to get results. We spend a lot of money on high meg cameras and programs such as PSP to give us 'quality' results. Leave everything on the highest setting and sit back and enjoy the results. Besides come print time a printer is more than capable of highjacking your settings and printing the way it wants to anyway.

Remember rule one. Never degrade a file unless you really need to. And if all else fails read rule one again.

I would recommend anyone wanting to 'play' with printing output to have a hard look at QImage. It's a program designed to maximize print quality.

regards

[df]

I agree with Brucet. I was advised a few years ago that it was absolutely paramount to resize my images to match the dpi/dimensions that the printing service I was using. i.e. if the printer had a native dpi of 600 dpi then match that for the 4x6 I was printing. So I did a test and made files that size and also made files of the same images in the original size (no resizing). Specified to turn all color corrections off at the printers end, etc... Got the prints back, shuffled them, showed them to my wife and a few other people. Nobody could tell the difference, myself included.

The thought that you have to match dpi of the printer to dimensions of the print was more crucial in early computers where the drivers didn't have interpolation capabilities. Early printers that had interpolation capabilities sometimes had flaws. But, if you're printing on anything made in the last 20 years you're probably good. After all they use the same software routines that you find in most graphics programs like PSP.

[hartpaul]

After I read the last link in my previous post some time ago I recognised that image dpi has no meaning with regard to website or monitor appearance. It is the pixel dimensions that are important.
Some olde monitors displayed 72 pixels per inch and modern ones may be 96 pixels per inch or higher not to mention the greater variety of phones, smartphones and tablets. . When you place an image on a website you have no way of knowing what the viewers will be using.
This article debunks the myth about converting images to 72 pixels per inch for web and monitor display"
http://www.photoshopessentials.com/esse ... tion-myth/

I set all my images to 300 dpi (and do not change the pixel dimensions) and leave it at that. Should I wish to print the image out then the number of pixels in my image and the printer device will decide what maximum size I can print the image at photo quality. Should I wish to print the image at a smaller size then I can specify that or I can resize the image pixel dimensions .