Preserved Topic: DPI (Page 1 of 1)

what's a good dpi to stick by? right now i usually just go with 172, but i'm wondering if i should go with more or what.

Edit: i also usually make my pictures bigger than i'm going to want them in the end and then shrink them when i'm done. is this a bad idea? i notice that sometimes it makes jaggies appear, but is there a way to get around that?



[This message has been edited by mantiS (edited 01-23-2002).]

Hmm..big question, but you haven't supplied the info needed to answer.

What are the images for? Print, Web, Reference? Will you be screen viewing them, making slides, printing expansions? What line per inch ratio is your printer using if it's for print...what's the colour depth...etc..etc...etc...

A good rule of thumb is to always make an image for web work at 72 dpi (as screen res won't read any higher than that, so if your res is higher it just means a bigger file that looks exactly the same.) However print images will always require knowledge of your printer or desired filesize to get a proper resolution for.

300-600 dpi used to be the industry guideline, but a better way to calculate is to go with twice the dots per inch that the printer will be using for output. So if your printer is printing at 150 lines per inch (LPI) then your image should be at or around 300 dpi. If it's a higher line count....do the math

As for making an image at a larger size, and then shrinking...well that can be helpful with paintings at times if you're planning on using them for screen presentation (interpolation seems to hide a lot of tiny massacres at times...heh) however if you're shrinking down significantly, you'll lose clarity and detail....ultimately "blurring" a lot of what you see. For "clear" tiny illustrations, it's usually best to work with very precise tools at the output size, and be quite detailed, to avoid all the blurriness and interpolation.

Hope it helps.

Peter

well it *is* going to be for the web, so i guess i shouldn't even bother making them over 72 DPI then. as for shrinking it, i usually make it about twice the size i'll eventually need it. i just do that so i can see everything better while i'm making it. also, i don't usually use fonts, and when i make my letters, it's just easier for me to make them big. well i'll try doing eveything on a smaller scale next pic i make.

thanks for your help.

-chris

sorry to double post, but actually, i did have another question. when i use lighting effects for something i'm going to use on the web, it looks fine when it's in photoshop. when i upload it and view it, however, there are what look like circles of colors instead of it fading smoothly. i usually save as .gif. does this happen because the web doesn't support all of those colors, or is it how i'm saving it?

My guess, mantis would be that you're not dithering your gifs properly and accounting for the numbers of colours. Gifs "band" colour and only support a maximum of 256 colours (which usually makes a chunky file size...but we'll go on)

Usually pieces that don't need transparency and need to have smooth grades in them are saved as jpeg files instead. If you check your dithering and number of colours when saving as a gif, you'll find the ability to properly optimize for web output.

I always go for the 72 DPI, but it's apparently not correct.

Dark G

quote:

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...72 dpi (as screen res won't read any higher than that, so if your res is higher it just means a bigger file that looks exactly the same.)

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Wayne Fulton, "Scantips"

quote:

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[...]We often hear that we should scan at 72 dpi for the video screen, like it's some kind of magic number. It's not. I know a few of the best sources tell us this, and I can't defend them, but it's very much less than the whole story. I believe an early Apple model described a 72 dpi monitor at one time, back before screen dimensions were adjustable, and we're stuck with it now, even without other evidence. There is nothing we can do with that number. For one thing, monitors vary today. [...] Some sources tell us "A computer screen displays images at 72 or 75 dpi."

They don't mean the image should be 72 dpi (unfortuneatey, some of them do). Video monitor specifications have no associated dpi number, and screens will simply show higher resolution scans as larger images (chapter 5). For example, there is no way you can fill a 800x600 pixel screen from a 6x4 inch photo if scanning at 72 dpi. It requires about 150 dpi. You will only get 432 x 288 pixels if scanning 6x4 inches at 72 dpi, and it will fill only about 1/4 of a 800x600 pixel screen. This is so very trivial to verify as true, but those that still parrot the false 72 dpi claim must not have ever bothered to look at the results they get. [...]

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Cheers



edit > UBB code

[This message has been edited by PunisherOlsen (edited 01-23-2002).]

Punisher: What is being discussed there is resolution in relation to measurable size (He's discussing graphic work done in physical inches and how at a higher scan res it would display larger on a screen)

72 dpi is a default measure of the pixels displayed in an inch on a typical PC screen at default settings. We use it as a standard since it keeps file sizes down while not truly effecting the screen based result. If people want to scan and print, that's a whole other kettle of fish.

When graphics are made specifically for web viewing on-screen, they should be measured in number of pixels (raster art, of course) as the "inch" is superfluous in these cases. If your image is set at an 800 pixel width, it will display 800 pixels wide on the screen, regardless of the resolution above 72. It will look smaller on screens that have higher resolutions etc. etc.

But it's still 800 pixels, displaying in the ballpark of 72 pixels for res. (we're ignoring apple's 96 pixel deal...shhhh...I said nada).

Test your the theory sans printer...no hard copies, just netware. Make an image at 800x600 pixels at 300 dpi, now resize it to 800x600 pixels at 72 dpi. view both on your screen.....see any appreciable differences?

Now check the file sizes....see a difference now?

[...]What is being discussed there is resolution in relation to measurable size (He's discussing graphic work done in physical inches and how at a higher scan res it would display larger on a screen)[...]

Erh, darn!

Wayne Fulton allmost made it as my new rolemodel

Cheers

I just replied in 'printing from ps'... but this seems more appropriate. In one of my books... it says that Mac monitors run at 72 dpi.... PC/windows based systems run at 96. <fwiw> <G>

....hehe

Cheers

DPI is "dots per inch", right? So, on Screen we could also say "Pixels per Inch".

Now if I have a 17"-Screen displaying 800x600 Pixels and YOU have a 17" Screen displaying 1024x768 px, how could we ever have the same DPI, be it 72 or 96 or whatever???



Beauty is only skin deep - ugliness goes to the bone.

Darkgarden, are you saying that the resolution would affect the file size?

It seems to me that the file size is only determined by the number of pixels. So if it is 600x800 at 300 dpi or 600x800 at 72 dpi would make no difference on the file size.

I create all my web images at 72, but I can't see what difference it would make if I decided to make them 100 instead. The number of pixels are still the same, and so is the size.

The only time the resolution would matter is when you print the image. And since most home printer want some 150-200 dpi, wouldn't it even make sense to save photos you display on the web in that resolution? That is, if you want people to print them out. (the difference will be that they will print out smaller, but with a better quality - less pixelated)

Or maybe I am just confusing things...

Confusing the issue completely...sorry ZOX.

I was fumbling when I mentioned file size, that's true. It tends to happen to me occasionally...heh.

The major difference that I wanted to deal with was file size itself...as in physical size when printed. The only reason to raise the resolution of a pic on a site is (as you mentioned) if you want people to be able to print it out.

You're correct that an 800x600 px graphic at 72 dpi would be basically the same byte weight as one at 800x600 px at 300 dpi...

HOWEVER, the file at 72 dpi will print out with a physical size of 8.33 x 11.11 inches....while the 300 dpi image will print out at 2.3 x 2 inches since the files have the same pixel count, but different pixel per inch counts.

Digging the problem? If you want the same file size at a print res, you'll get a tiny (but crisp) version of the image when printing.

So..it seems a bit pointless really.

one thing to also take in count is that if you are working in higher dpi.... its much easier to shrink something.. then it is to enlarge something

As long as we're on DPI, is there a difference between DPI and PPI? And what unit is used for "dots per inch" in halftone screens for print? Does a 300dpi TIFF really come out at 300 halftone dots per inch (barring any conversion by the printer), or are they two completely different measures?

From Sue Chastain at About.com's Graphic Software site:

Resolution is a measurement of the output quality of an image, usually in terms of samples, pixels, dots, or lines per inch. The terminology varies according to the intended output device. PPI (pixels per inch) refers to screen resolution, DPI (dots per inch) refers to print resolution, SPI (samples per inch) refers to scanning resolution, and LPI (lines per inch) refers to halftone resolution.

For further discussion on the topic, have a look here:
http://graphicdesign.about.com/library/weekly/aa070998.htm



[This message has been edited by Eggles (edited 01-27-2002).]