i want to put a website together of my photography. i would like to know what settings people use when scanning there images. what dpi? what width they set there images at etc. i am trying to cut a balance between a easily downloadable files and still showing detail. i know that there are huge variables in what i am asking you to help me with. but suggestions would be appreciated.

-- john molloy (ballyscanlon@hotmail.com), April 15, 2002

Answers

John,

For the web you want to size your images at 72dpi, then they will display at 'about' the size you intended depending on other peoples setups/monitors. If you have the disk space scan at the full native resolution of your scanner then downsample for saving as a jpeg for display. Do all your sharpening at full size, and any tonal adjustments in 16 bit mode if you can.

Larry

-- Larry Roohr (lrryr@attbi.com), April 15, 2002.

so is "sharpening" something you do to make up for something lost in the scanning process? or is it an add on?

-- john molloy (ballyscanlon@hotmail.com), April 15, 2002.

I try to scan at Max res (4000dpi, 14bit per channel), but need to buy a new hard drive because i am running out of space so now my originals are sometimes smaller. That way i only need to scan once for posting on the web or printing. Then, for posting on the web i normally try to resize so the "long" side of the 2:3 picture is about 600 pixels (and the short end is about 380-400 then... this is to allow people with 800x600 resolution monitors (the smallest one would have to deal with these days), to be able to view the picture in full screen mode whether or not it is a portrait or landscape image. the DPI doesn't matter if publishing as 8bit per channel JPG's for web use because all monitors care about is the pixel resolution. For the web I wouldn't save the image at a level of 12 jpg compression (in photoshop 6), but rather at 7 or 8 this substantially reduces the file sizes. In general a good goal is to keep images less then 50kb in size if at all possible so the modem users don't complain. Examples of these sizes of images are available here: http://www.photo.net/photodb/folder? folder_id=91748 I personally think this is a good balance of file size and image viewability.

-- Matthew Geddert (geddert@yahoo.com), April 15, 2002.

For the web you want to size your images at 72dpi,

Don't do this. DPI are irrelevant for screen presentation. Scan at a reasonably high resoluttion (like 1k) and then resize to something reasonable (like 600x400). Do not bother changing the dpi when you resize .

I usually target an end size of 600xwhatever for horizontal and 400xwhatever for vertical. This generally keeps your image size within typical browser window sizes.

Do all your sharpening at full size, and any tonal adjustments in 16 bit mode if you can.

Sharpen at your final size, not full size. If you sharpen the original scan (which I assume is what "full" meant), you will get artifacts when you resize. Also, always sharpen with Unsharp Mask, never with other sharpening options and never in the scanner software.

Also, for truly effective sharpening, read Dan Margulis' article on the web about sharpening. You do always need to sharpen a scan, it corrects for the loss of sharpness in the scanning process. It cannot correct for flatness issues with low cost transparency adapters.

I have found that it is far more effective to sharpen in LAB space. Convert from RGB to LAB, deselect the A and B channels, and sharpen only in the L channel. You can apply a very heavy amount of unsharp mask in the L channel without visible sharpening problems.

-- Jeff Spirer (jeff@spirer.com), April 15, 2002.

John,

Sharpening helps with most scans, and is also the most easily overdone step in the process and can add artifacts quite easily if overdone. Oversharpen and a quick look will tell you you've improved the image, a close look will reveal the problems. If done properly the effect will be subtle, and artifacts at a minimum. Also unsharp mask is the filter to use, as mentioned earlier.

Larry

-- Larry Roohr (lrryr@attbi.com), April 15, 2002.

The DPI setting controls two things - the size of the digital image when scanning (how much image data you extract from the original), and the size of the print when printing. Once digitized, it has no effect on displayed images, as noted by others - a pixel is a pixel. The "72 DPI" thing is a web myth dating back, it appears, to the resolution of the first Mac displays.

When scanning, you have a couple of options. One is to scan for web only, keeping the original size of the scan fairly small, and scan separately at a higher resolution for digital printing. I prefer to scan at high resolution, sized for the largest digital print I might make from the scan. Then, I do any retouching needed only once, saving the original scan in Photoshop format (PSD). Once saved as a .psd, I resize in steps, no more than a 50% reduction in size, pixel-wise, for each step, running unsharp mask at each step.

The key to unsharp masking without introducing artifacts is to adjust the degree of sharpening (radius and % in Photoshop) to an appropriate level for the size of each image. For large scans (20MB - 60MB) I often use a radius between 1.6 and 2.4 and an amount of 50%-65%. That reduces in stages to a radius of around 0.4 for a 600x400 size image. A light touch is far better than a heavy hand when sharpening.

Another tip is to save as JPEG only at the final stage when the image is down to the size you want for display. JPEG compression throws away image data, so you don't want to compress an already-compressed image. The ideal is to have the "large" version of the image around 60-70 KB in file size, balancing between size and image quality.

Scanned from an 8x10 print at 300 DPI, and reduced in Photoshop:

-- Ralph Barker (rbarker@pacbell.net), April 15, 2002.

The 72dpi was indeed the screen resolution of the Mac, PC's were 92 or so, not a myth at all. I'm sitting in front of my 17" monitor, 14" across at 1024 pixels, divide that out and guess what, 73dpi. So it's just a rule of thumb thats worked for me, no more. When I size for the web I set the dpi to 72, set the width with constrain proportions on and let it resample. I do all my adjustments at full resolution, including sharpening, get the image the way I want it, then downsize. Different strokes.

By the way, for quality sharpening without a lot of fuss I'd recomend Ultra Sharpen Pro, do a web search. It's about $25 and was well worth it to me. Or if you do a search on sharpening you'll come across techniques to do the same thing manually, or write your own action.

Good luck,

Larry

-- Larry Roohr (lrryr@attbi.com), April 15, 2002.

Larry,

Here's an interesting experiment for you. Take the original file for an image that you already resized, change the DPI to 4000 in Photoshop, set the pixel dimension as you normally would to the reduced size, and let it resample. Then, compare the result with the image you previously resized, both with respect to the pixel dimensions and the resulting file size. Both files should be the same size, and display exactly the same. Or, do the same sort of thing with an existing image - simply change the DPI setting. The image will display the same, and still be the same size in terms of KB.

Unless the application is configured to use DPI as part of the resizing process, it's just data that is carried in the file header for eventual use when printing the file. The "myth" that I referred to is that setting the DPI of a digitized image has some effect on its display. The display is based on the number of pixels in the image file and the configuration of the monitor and graphics card displaying it.

-- Ralph Barker (rbarker@pacbell.net), April 15, 2002.

Every time I have to scan slides I learn something new. I use Vuescan, which has the most impenetrable interface of any application in recent memory, but which always brings home the bacon. One thing I figured out just now is to set the brightness control to less than 1 - I now set it to 0.9 - which stops high contast areas (white against a very dark background, for instance) from flaring out, and white/black point to 0 each. These settings get me very rich, clean scans. I also use the generic colour slide setting in the colour tab. I always scan at 2700 dpi and resize to whatever's convenient, and am very careful of over sharpening (usually around 50%, 0.7, 1). I never try to second guess my scanner's colour rendition by playing with it on-screen, but I do use the midtone or highlight droppers in levels to set a neutral tone or white point if the overall lighting has a strong cast - like the picture of the girl in the cave I posted on the 35 summilux thread - although you can't always get rid of it all, but just enough to make it less annoying.

The dpi thing is really only relevant to print - a monitor just displays the pixels, so you don't need to worry about it. But if you're using Acrobat, then dpi does come into it, as the system will then interpret your screen as a 72 dpi printer. And no doubt there are other quirks out there I don't know about.

All of this is just my own approach, and as I said, every time i do a major scan job I find out something new. I do recommend vuescan, just wish Ed Hamrick would get someone to design his interface for him.

-- rob (rob@robertappleby.com), April 15, 2002.

Final point re: sharpening: high res monitors can mislead you about the results of sharpening and image quality overall, because the pixels are so small. I have a 15" UXGA+ monitor on my laptop which has a 1600x1200 resolution, and things always look good on it, but often look crap on an internet café CRT monitor set to 800x600. On the other hand, IME laptop screens give much better colour straight out of the box than CRT's.

Basically, the whole thing's a minefield. After about two years of fiddling around you'll begin to have an idea of the issues and how to resolve them to your own taste (if you're a slow learner like me), and that will still be very different from what other people do. Good luck!

-- rob (rob@robertappleby.com), April 16, 2002.

I agree with most of what's already here (except the self-contradictory parts!!)

RE size: I 'size' stuff to 9.9 inches x 6.5 inches and 72 dpi and it works - they come out roughly 10 inches long on my posts. But anyway 600-700 pixels along the longest side is the high end for quality/fast download - and 350-400 pixels (roughly 5.5 inches) along the longest side is about the low end if you want an image with some quality to it.

RE sharpening; like they said - do it ALMOST last (see next section) and do it gently - you just want to restore some of the edge crispness that was lost in scanning and resizing. I use Unsharp Mask/135%/.3 pixel radius for final web images. I've never tried the LAB channel sharpening myself - but it is how the scanning people do it here at the newspaper.

One last warning - be very careful to NEVER run an image through the .jpg process more than once - i.e. don't keep opening it and resaving it and reopening it etc.et.c once it's become a .jpg. JPEG compression loses data and creates artifacts, and every time you use it you creat new artifacts on top of the old artifacts. JPEG an image ONLY once you are absolutely completely finished with all alterations - think of JPEG as the brown paper wrapping you put on ONLY when you're ready to ship.

The same with GIF.fing or any other compression technique for the web - do it last and do it only once.

-- Andy Piper (apidens@denver.infi.net), April 16, 2002.

Hi Ralph,

" The "myth" that I referred to is that setting the DPI of a digitized image has some effect on its display."

Oh, ok, Your right about that. But what's missing is that part of the goal here is to minimize file size for download, to send a bigger file than nescessary and have the browser downsize/interpolate for display isnt good economy, if you size at the target screen resolution you've maximised quality and minimized filesize. 72 dpi is going to be about right for most displays. Lots of ways to skin a cat.

-- Larry Roohr (lrryr@attbi.com), April 16, 2002.

But what's missing is that part of the goal here is to minimize file size for download, to send a bigger file than nescessary and have the browser downsize/interpolate for display isnt good economy, if you size at the target screen resolution you've maximised quality and minimized filesize

This just is NOT true, as was stated several times above. As someone pointed out, the dpi info is part of the header. I have scanned at 4000 dpi, resized to 600x400, and gotten the same size file as resetting the dpi to 72 and the size to 600x400. It's irrelevant.

-- Jeff Spirer (jeff@spirer.com), April 16, 2002.

"This just is NOT true, as was stated several times above. As someone pointed out, the dpi info is part of the header. I have scanned at 4000 dpi, resized to 600x400, and gotten the same size file as resetting the dpi to 72 and the size to 600x400. It's irrelevant."

Of course you'd get the same size doing that. On my screen your 400x600 image will display at 5.5" wide by 8.3" tall at it's native resolution. Thats fine if thats the size you intend. If you send that same file and size it to 4x6 for instance, you've sent a file almost twice as big as it needs to be because my browser/video card will downsize it to that for a smaller display. Wasted bandwidth.

Hmm, but you know I've never considered what happens with jpeg compression to this reasoning. Nice bucket o worms heh?

-- Larry Roohr (lrryr@attbi.com), April 16, 2002.

Larry, unless you have a very exotic video card/driver, a 400x600 pixel image will display at 400x600 pixels regardless of the dpi. The only exception I'm aware of is when using an impagination program like Pagemaker, because it thinks in terms of print resolution. I really do think Jeff's right here, at least it certainly corresponds to my experience on a range of machines.

-- rob (rob@robertappleby.com), April 16, 2002.

Larry, unless you have a very exotic video card/driver, a 400x600 pixel image will display at 400x600 pixels regardless of the dpi.

Exactly. Believe me, I understand this. I am doing professional scanning (for pay) right now, among other things. The DPI setting does not affect display, nor does it affect file size for a fixed pixel dimension.

-- Jeff Spirer (jeff@spirer.com), April 16, 2002.

I dont think we disagree, let me restate what I've been trying to say.

For the case where pixels are displayed at the display native resolution: I believe most displays are set at around 72dpi (measure the size of your display and divide it by the number of pixels in your driver setting), so I prefer to set an image to 72dpi, then set the size in inches I desire it to be displayed at, and resize that way, the resulting pixel dimentions will end up matching closely in size, on most monitors, to the inch dimensions I input in the resize box, 5x7 will be about that, and 2x3 will be about that, it's just how I prefer to do it. This is because most displays end up at around 72dpi when people set them for comfortable viewing, IMO.

For applications that will resize on the fly (Word does this, for instance) having larger pixel dimentions than is necessary (the application downsizes) is wasting space/time etc. Best to match the pixel count to the desired display size. Re-reading I see that I misunderstood Ralph somehow and thought he was talking about this case, my mistake.

-- Larry Roohr (lrryr@attbi.com), April 16, 2002.