Hi,

I've been reading about stuff from this forum ever since I got my m6 about a month ago. I was wondering what is the general rule regarding resolutions of scanned images for decent 8x10 print outs? Or perhaps somebody could direct me to a webpage that explains this whole thing. I think that 160 ppi is the general rule for web images. Is that right?

Thanks! Ken

-- Ken Kwok (kkwok@gostanford.com), September 15, 2001

Answers

I would not print anything at less than 250dpi (or 2000x2500 for an 8x10) and I usually go between 300-600dpi depending on the printer I use. But that's just me. I'm sure that others have a other ideas.

-- Josh Root (rootj@att.net), September 15, 2001.

Same as Josh: for inkjet prints up to 12x18 you need at least 200 pixels per inch in the final image size, and I use 250 as a standard.

If you are going to make really big prints (like 4x6 feet or something) you can often get away with the same total resolution (image file size) as a 12x18, because viewers will be standing further away from the picture.

Most computers only show 72-100 ppi on screen, so there is not much point in going higher than that for web or .pdf or presentation display (unless someone is going to 'zoom' in on the picture.). And a 72 ppi image will load about 4.5 times as fast as a 160 ppi version of the same image.

Frankly, back in the bad old days (1995) when I had sl-o-o-w computers, scanners, and 600 dpi printers, I did OK with 120 ppi images for print. But, as with most things computerized, more is better, so use the largest file size you can comfortably handle. It's very hard to see much difference once you get above 250 ppi, which at the largest viewing size on screen makes a 6.5" x 10" image look like a 23" x 35" blow-up.

-- Andy Piper (apidens@denver.infi.net), September 15, 2001.

Andy, I wonder about your screen resolution comment. As I understand it, the only thing that counts in screen display is the total pixel count, although some browsers will resize images to fit the screen. But in a screen display dpi x linear dimension = number of pixels in that dimension, and that is generally displayed at 100%, so increasing the dpi is neither here nor there.

Tell me if I'm wrong.

BTW, I'm still waiting for my yellow hasselblad replica.

-- rob (rob@robertappleby.com), September 15, 2001.

Output dpi is really a function of the printing engine. You generally want your output dpi to be about 1/4-1/5x the max resolution of your printer for best results. I use printers with 1440 dpi print capability, so I try to keep my print resolution files at 266 to 350 dpi.

For screen display, pixel count is all that really matters. Modern displays range from between 72 dpi to 125 dpi, but you have no control over what your viewers might have. The number of pixels in your image will affect the size of your image and ultimately how much detail it will display. Since there are those with as little as 640x480 pixels and up to 1600x1200 (or even more) on all kinds of sized displays, you have to compromise. I figure that the majority of viewers have between 800x600 and 1024x768 sized displays, so I size my web images to fit into a box 600 pixels wide and 510 pixels tall so that most everyone can see the whole image without scrolling.

-- Godfrey (ramarren@bayarea.net), September 15, 2001.

Okay this may throw the cat amongst the pidgeons. Before you consider what dpi you print for, what resolution are you scanning your images at? This is the first step in the chain.

Now consider the resolution of the film (assuming you are scanning 35mm neg/tranny). If you scan a 35mm frame, 100 ISO, at 4096 pixels across length wise, you should capture the resolution of the film itself. ie. the pixels are smaller than or equal to the size of the grain. Ideally you want the pixels to be smaller than the grain, so the higher the res the better... to a point, the rest is a waste of time.

dpi is concerned with real world units of measurement, but the image/ file still has the same amount of pixels across and down from the original scan. Lets take a a scan that resulted in 4096 pixels across the 35mm frame. Now change the dpi of that file and the only thing that changes is the physical size, ie the real world print size.

4096 @ 150 dpi = 27" x 18" printed image size " @ 250 " = 16" x 11" " " " " @ 300 " = 13" x 9" " @ 400 " = 10" x 7"

The amount of information within the file remains the same. The output size is only interpreted differently. The image is still only 4096 elephants across!! The printer is only ever goinig to print from the information it receives. Be sure to retain all of your resolution from the scan and then size it (inches, cm's) how you see fit, let the print dpi sort itself out.

I hope that has answered your question. I work in film visual effects and use Photoshop every day. We don't concern ourselves with dpi, only the amount of pixels across the frame, which we then print(film record) back onto film.

If I have not been clear with this explanation, please let me know and I will try to clarify it.

Regards

Wayne

-- Wayne Haag (wayne@wetafx.co.nz), September 16, 2001.

Rob: I can't tell you you're wrong OR right. My eyes cross when it comes to actually dealing with web software, so I have no idea to what extent images get resized by browsers and what (if anything) determines how they will look on screen.

What I DO know is that I upload my images to Photonet at the final size I want them to appear (e.g. 6" x 9") and at 72 dpi, and they show up the way I intended - Thank goodness!

-- Andy Piper (apidens@denver.infi.net), September 16, 2001.