why do 72 ppi images look good on a display but bad in a print?

Web resolution is at 72ppi.

Color photography and magazine printing is around 300ppi.

Why does a 5x7 at 72ppi viewed on a monitor look good whereas a 5x7 printed at 72ppi doesn't. A technical explanation from someone would be appreciated.

Thanks.

The simple answer is that monitors don't really "do" ppi.

Do you know what resolution is and what does 72dpi mean? That'd be a good starting point...

I also notice that you make a reference to 'web resolution'. Images on the web do not have resolution, they simply have a height and width expressed in pixels.

kkamin wrote in post #9534647
Web resolution is at 72ppi.

Huh? Perhaps your monitor has 72ppi, but I don't think you can generally state "web resolution" as any particular number. But yes, most folks' monitors have resolution between 72 and 100 pixels per inch

kkamin wrote in post #9534647
Color photography and magazine printing is around 300ppi.

Why does a 5x7 at 72ppi viewed on a monitor look good whereas a 5x7 printed at 72ppi doesn't. A technical explanation from someone would be appreciated.

Monitors just have lower ability to resolve dots than print does, and given that they generate images via light rather than by ink, the way we see them is different. But certainly if you get up close to a monitor, especially if its a 72ppi monitor, you can tell it's not as sharp as 300ppi print.

Dave

Web resolution is whatever is the resolution of the monitor displaying the web. However that doesn't invalidate your question because the usual resolution of modern monitors is in the 90 - 100 ppi range.

An image sent at a low ppi, be it 72 or 100, to be printed is first of all resampled by the rip/driver to (usually) 300 ppi. It is this uprezzing that lowers quality.

krb wrote in post #9534729
I also notice that you make a reference to 'web resolution'. Images on the web do not have resolution, they simply have a height and width expressed in pixels.

Okay, but most monitors currently hold 72ppi to 100ppi (I know there are monitors that have more ppi but forget about that, I don't have one and most of my clients don't have one yet). If I view a 4x6 or a 288x600 pixel image up to a 4x6 that was outputted at 72ppi and printed, the print would look soft and bad (especially at that small size). I don't understand the disparity of viewing x amount of dots in a space or x amount of pixels in an identical space.

Also 'web resolution' does exist. It is a term used in design, video production, photography etc. to describe an output going to a computer display.

Besides, that. Everyone who isn't contributing to an answer but picking out things like 'web resolution' to criticize are missing the point. You know what I mean. You correcting my terminology doesn't change the question.

This is the weakest part about forums. People just want to argue or engage in some inconsequential technical debate. Just contribute an answer or move on. Everyone knows what this simple question is. Thank you.

tzalman wrote in post #9534798
Web resolution is whatever is the resolution of the monitor displaying the web. However that doesn't invalidate your question because the usual resolution of modern monitors is in the 90 - 100 ppi range.

An image sent at a low ppi, be it 72 or 100, to be printed is first of all resampled by the rip/driver to (usually) 300 ppi. It is this uprezzing that lowers quality.

Thanks for the reply. So you are saying that printers print at 300 ppi and anything lower is rezzed up, and therefore causes the interpolated look? But why couldn't printers lay down 72 ppi and make it look good?

They can... If you print a web size image, at it's native size, it is just much smaller on the printed page, that's all.

In order to get an image to fill the page at full quality, it needs to be higher resolution than a 72dpi image.

That's why print designers need/use higher res images in their print ads, etc.. because if they use web images, they will turn into pixelated goo at full size on paper. They can be used, but they will just be much smaller in order to keep the quality acceptable.

kkamin wrote in post #9534896
Thanks for the reply. So you are saying that printers print at 300 ppi and anything lower is rezzed up, and therefore causes the interpolated look? But why couldn't printers lay down 72 ppi and make it look good?

Printers print at whatever dpi they were designed for. I think it's usually 250dpi for pro labs.

72 dpi is simply not enough information for a 4x6 print viewed at normal distances. It's the same idea as pixellation from not having enough pixels.

The human eye can resolve a certain amount from different distances, and for the viewing distance of a 4x6 (reading distance, basically), it can resolve around 250-300dpi, assuming 20/20 vision. As you print larger, the viewing distance increases, and the required dpi for an acceptable print slowly decreases.

And most monitors have moved past 72dpi by now. A 15.4" laptop at 1280x800 (i.e. nothing special) has about 100dpi. 20" monitor at 1680x1050 also has about 100 dpi. I doubt many recent monitors or laptops are below 90dpi at this point.

72 dpi is just that 72 dots (pixels) per inch so at 300 dpi you have 300 pixels in the same area whereas the 72 dpi image only 72, with 300 giving it more detail. Newsprint is only at 150 to 200 dpi. Trying to print at a higher dpi on newsprint puts you in the danger of ink bleeding together since newsprint is so porous. Taking all of the into account billboards are only 15 dpi but since you're seeing them at such a greater distance it actually looks better then a 72 dpi printed piece up close.

Technically anything on a monitor is measured at ppi (pixels per inch) only actual printed material is dpi (dots per inch).

It's because LCD monitors displays images better and larger than print technology. As the OP said, a monitor can display an image very well at 5"x7" 100% view but those same pixels printed at 5x7 won't look good.

LCD screens can make larger pixels look better than a print can.

HappySnapper90 wrote in post #9537058
It's because LCD monitors displays images better and larger than print technology. As the OP said, a monitor can display an image very well at 5"x7" 100% view but those same pixels printed at 5x7 won't look good.

I totally disagree with that. If you have your monitor calibrated correctly when you send something to the press is will look as good as on screen. Anytime my prints don't look as good as it does on the screen, then it's time to calibrate the monitor. Which is one of the main reasons for press checks.

I will agree with you that a 5x7 100% view of the image printed out at 5x7 will not print out as good if you're looking at a 72ppi image on the screen. If you're working on an 5x7 image at 300ppi that will result in an image 1500 pixels x 2100 pixels but if you're working on an 5x7 image optimized for web at 72ppi that will result in an image at only 360 pixels x 504 pixels. They will print the same size but the image at 300ppi having 4.16 times as many pixels per inch will print at a higher quality, better looking image.

What a bunch of lame answers.
It's freakin' late for me, and what i wrote below isn't my best linear lecture by far, but I was compelled to try to get this info off because of responses like "thats the way it is."

Monitors display 72-75 pixels per inch. A pixel is the smallest "picture element", hence, the term.

Print output is dots per inch, dpi. Similarly, lpi is lines per inch. Printed halftones are measured in lpi. It takes a 2400 DPI imagesetter to produce a FULL RANGE of gray at 150 LPI.

Here's the math: (Resolution divided by the line screen) squared + 1 = number of grays that will be output (256 optimum, as in all the gray information in a photoshop channel).

BTW, You can tell even a 600 or 1200 DPI output device to generate ANY LPI you want, but you will get far less shades of gray. Banding will occur, but at the LPI you chose. A 1200 dpi imagesetter can only produce (if I recall correctly) a 106 LPI film doing 256 shades of gray.

Your answer is here somewhere. Offset printing an image at the standard 150 LPI (again, requiring a device that can do 2400 DPI to get a full range of tones), requires an image resolution (at 100% of usage size) of twice the line screen; everyone knows the famous 300 dpi. (Use the formulas above to prove this.) A good looking screen image (72 dpi) is roughly 4x too small.

Actually, of the 4 CMYK seps, the range of LPI per channel ranges from 120-150, at different angles, to avoid moire. The pattern of dots (or diamonds, or squares, or whatever the operator chooses) is called a rosette. Each photoshop channel can hold a max of 256 shades of gray — channels are just grayscale info with a color over it.

Line art is different. Since there is no halftoning involved, the art needs to have the SAME res as the output device. 2400 DPI output needs 2400 PPI line art.

If this thread is still going tomorrow, I'll try to be clearer when I wake up. The short of it is, there's no halftoning going on in your monitor. The difference in image presentation has to do with the halftoning process.

mcluckie wrote in post #9537265
Here's the math: (Resolution divided by the line screen) squared + 1 = number of grays that will be output (256 optimum, as in all the gray information in a photoshop channel).

I'll have to disagree on that, at least with commercial presses. In order to effectively utilize the entire range of available LPI in a halftone system, an image selected for printing generally must have 1.5 to 2 times as many samples per inch (SPI). For instance, if the target output device is capable of printing at 100 LPI, an optimal range for a source image would be 150 to 200 SPI. Using fewer SPI than this would not make full use of the printer's available LPI; using more SPI than this would exceed the capability of the printer, and would be effectively lost.