Improving quality of image..dpi?

hi ppl…im new here, hope im in the right category… i want to print some images, but im confused by how big my size can be… i know there is resolution, that has direct impact on size, but also dpi, which as i understand has direct impact on quality of print… ive been reading about it in few sites and print stores online, but everyone has different opinion… my res,for example is 2000x3000. some say i can do 8"x11,but some say i can go bigger because i view it from a further distance.
im in to sound and music, and i know its all about the source, if my source is low quality file, converting it to hi quality would not help,u would actually hear the “flaws” better, so it will be even worse then the low q file! is it the same with image files? there r sites that let u convert res and even dpi… would it help or i will loose quality? my dpi is 72 and i know u need at least 300, any help would be greatly appreciated…even pointing me in the direction of other posts or sites,will be great…cheers

300 is only relevant for images printed using lithographic printing. Which is only really done for large amounts of prints for books/magazines/leaflets and all those things. It can be used for smaller print runs too and prints many different sizes.

300 DPI for print has arose from the simple equation of mulitplying the output devices LPI (Lines Per Inch) x 2 to get the best DPI for print and most printers would be set to at midrange 150 LPI.

However, newspapers use a lower LPI - which means even at 80 LPI the DPI would 160. And at 120 it would be 240.

This is still wrong though.
As the LPI should be multiplied by 1.41 - and I’m guessing someone at some point rounded up to 2 to make it easy to multiply.

All this is only relevant for things printed and viewed at arms length in a reading scenario.

The 1.41 comes from a halftone dot being rotated 45 degrees for print.

If a square is size 1 all around. Then the length from tip to tip is always 1.41.
Basic math.

You are right - the more you increase the resolution the more you see the flaws - as with your sound files

You’re printing digitally probably. So this will come as s surprise to you but for Litho print at 150x1.41 is only 211.5 DPI.
So that would be fine for LItho Print.

But in Digital it’s a bit more forgiving, due to different print methods, substrates (like papers), inks etc.

You could actually be perfectly fine at 150DPI or even lower.

It also depends on the content of the image.
On a persons face the flaws might be noticeable due to the way people can detect details in familar patterns.
However, in a foggy mountain scene, you probably wouldn’t see the flaws at all.

What’s the correct DPI?

Whatever the print vendor recommends.

cheers… thats a bit confusing… but i understand converting the res will not help, what about dpi? the print vendors go between 150 to 300, most recommend at least 150… if i convert it would it help? r they in ratio with each other? i.e f i have an image of 2000x3000 and 300dpi and i resize it to 4000x6000 that means my dpi will be 150 now (automatically)? ive tried a site of conversion but every time i resize the image it comes up as 96dpi, no matter if i resize it by 25% 50% or 100%…dont know why…

There’s no room for opinion on this. There’s factual information and misinformation.

First, I agree with @Smurf2. Both of us have been in this business for decades, and this subject is second nature to both of us. Unfortunately, the answers get a bit technical and are not especially intuitive, which I suppose is why so much misinformation abounds.

I’ll try to explain it a little differently than Smurf2 in the hopes that between the two of us, you’ll pick up on it. Really, though, we’re saying the same thing.

Some people use the term dpi (dots per inch), but the proper term is ppi (pixels per inch), so I’ll use ppi. In printed materials, resolution is expressed in terms of the number of pixels used to print a one-inch-long row of halftone dots. In printed material, resolution and ppi are, essentially, the same thing.

If you look at a magazine with a magnifying glass, you’ll see the photos are composed of small dots. These are halftone dots used in litho/offset printing. There are typically (but not always) 150 halftone dots printed per linear inch. This measurement of the number of halftone dots in a linear inch is the lpi (lines per inch). The rule of thumb is that two pixels are needed per halftone dot. In other words, if the lpi is 150 halftone dots per linear inch, 300 pixels are needed for optimum print quality.

In reality, 300 ppi is more than enough, but the extra pixels provide a bit of wiggle room in case the photo needs to be cropped or enlarged a bit.

In a newspaper, the lpi might only be 100 (100 halftone dots per linear inch), so following that same rule of thumb, the ppi resolution only needs to be 200 instead of 300 pixels per inch. A billboard seen from hundreds of feet away might only need a ppi resolution of 90 since the image only needs to look sharp from that distance.

A key concept here is viewing distance and the required sharpness at that viewing distance. For something held in one’s hands at read from 18 inches away, 150 lpi with a resolution of 300 ppi is typical. Since the viewing distance of a billboard is much further away, the ppi resolution can be correspondingly lower.

With that in mind, digital printing has become popular in recent years as the technology has developed. Unlike the halftone dots of litho/offset printing that I just described, digital printing doesn’t use halftone dots. Instead, the ink is sprayed onto paper (or other material). This is very similar to the inkjet color printers many people have in their homes, but the quality is much higher.

Short-run print jobs (when there are fewer than, for example, a thousand copies being printed), digital printing is typically used. For larger jobs, litho printing becomes less expensive.

Fortunately, the 300 ppi resolution rule of thumb is still more or less applicable to high-quality digital printing, even though there are no halftone dots. For something typically seen from 18 inches away, 245–300 ppi will work out great (if not a bit overkill). A poster intended to be viewed from, say, no closer than three feet away, the resolution, like with the billboard, can be lower. Printing a poster at 150 ppi would work just fine (unless there is a bunch of small text reversed out of the image or embedded directly into the image, in which case, I’d want the resolution to be higher).

That 2000x3000 pixels isn’t resolution; that’s the size of the image. The resolution would be how many of those pixels are used per linear inch when printed. If we use the 300 ppi rule of thumb, (math required here), that image has enough pixels to print at approximately 6.5 x 10 inches. As I said previously, though, 300 ppi is just a rule of thumb, and a resolution of 250 ppi will work just as well, so at 250 ppi, you have enough pixels at that resolution to print an 8 x 12-inch image.

However, if the image is printed on a poster designed to be viewed from a minimum of, say, two or three feet, you can likely get by with 150 ppi, which would enable that 2000x3000 pixel image to print at approximately 13 x 20 inches.

Yes, it’s very much the same thing.

If you’ve understood what we’ve said, so far, you’ll realize this question makes no sense. The 72 ppi is only meaningful if you print the file using 72 pixels per linear inch. What’s relevant is the pixel dimensions of the image. Using your 2000x3000 pixel image, at 72 ppi, that image would print at approximately 28 x 42 inches, which would be very blurry at anything less than a couple of hundred feet away. As I mentioned, at 300 ppi, that exact same 2000x3000-pixel image would print at 6.5 x 10 inches.

I don’t know anything about the websites you mention. However, as you mentioned, if they sample up the data to, say 4000x6000 pixels to achieve a higher resolution, that’s sort of pointless.

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Sorry if it’s confusing.

Typically the 300 only really applies to a certain print method which you likely won’t be using. And it only really applies to things read at arms length like leaflets brochures booklets books etc.

Posters don’t require that much and yours most likely will be printed digitally.

And posters are viewed at a distance so you don’t need to be so high with the resolution.

If the content is a face or faces really low resolution will be obvious.
For non recognisable objects like foggy scenes it likely won’t.

So there’s some variables to consider in terms of ‘getawayability’.

If your image is 2000x4000 @ 72ppi
Your size is inches is just a division.

2000/72 = 27.71
4000/72 = 55.55

Size is 27.51 inches x 55.5 inches

As you reduce the size the 72 increases.

So at 13.75 in x 27.75 in(roughly)
Would mean you still have 2000x4000 pixels
But packed more densly into 150 PPI (pixels per inch)

72 PPI wouldn’t be good for print, except maybe newpapers and billboards.

Billboards I’ve printed as low as 30ppi.

Posters should be fine at 150 or higher

And books brochures etc around 240 to 300 PPI.

Sorry for using dpi and PPI so loosely

thanks guys…i think i got it, the relation between the two… the ppi is the quality factor, at least for the printing stage, when you set up the scan or the camera.res is the size of the image. so an image with high res size, but low ppi ,can have same printing size end result, with another image that have low res size but high ppi… just-b simplified it more ,but smurf2 gave me the formula that eluded me… i was dividing the ppi by 2 and multiplying the res. .but res stay the same, the size will be doubled after the division of the new ppi factor… that was tricky for my brain :wink: explaining and simplifying is a good ability to have guys… thanks again…

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