Display, Printing, DPI and PPI

For Windows XP users:

One easy way to resize picture is by using XP Powertoys that allows you to right-click on the image icon to resize. It's fast and easy. And it is free. It is available from Microsoft's website.

Another option is powerful imagemagick software. For example to make a thumbnail (from the docs) use the convert program like ..

convert -size 120x120 cockatoo.jpg -resize 120x120 +profile "*" thumbnail.jpg

In this example, '-size 120x120' gives a hint to the JPEG decoder that the image is going to be downscaled to 120x120, allowing it to run faster by avoiding returning full-resolution images to ImageMagick for the subsequent resizing operation. The '-resize 120x120' specifies the desired dimensions of the output image. It will be scaled so its largest dimension is 120 pixels. The '+profile "*"' removes any ICM, EXIF, IPTC, or other profiles that might be present in the input and aren't needed in the thumbnail.

for more info check out http://www.imagemagick.org/

There are a variety of resizing tools available. The best known is Genuine Fractals (http://www.lizardtech.com/solutions/gf/). There is also PhotoZoom (formerly S-Spline, http://www.trulyphotomagic.com/shortcut/customer/home.php?cat=3&sub=serie.info} and Extensis pxl SmartScale (http://www.extensis.com/pxlsmartscale/index.html?ref=hp). Many people use Fred Miranda's Stair Inerpolation action or plugin (http://www.fredmiranda.com/software/). I do all of my printing through Qimage (http://www.ddisoftware.com/qimage/) which resizes the print as it spools it to the printer. Therefore, I do not have to resize the file before printing (great for file storage). Qimage comes with a host of other features. Some people do not like its interface. But it is only $44.95 and it comes with free upgrades for life. I recently compared each of these methods by resizing an image to 13x19. I cropped a 5x7 segment and printed a sample of each. I found Qimage to offer the best resizing of the five options. Chris Fuller

Another tool MS Photo Edit, which comes with MS-Office, can be used to resize the images too, although it's not a great tool. One comment regarding dpi for the printers, it's dots of inks, not the pixles of the images. It usually takes a lot of dots to get one pixle with perticular tone. Therefore, you do see better result if you use photo paper and higher dpi setting for the printer. However, this doesn't mean you are getting higher pxi in your print.

Another important operation besides resizing is image rotation, typically done just after pulling the images off your digicam, prior to archiving them. The JPEG format can be rotated without decompressing it, which means that the operation is fast, and there is no quality loss.

But not all programs are capable of doing that: many will decompress the JPEG to whatever internal format they use, rotate it, and then recompress it. One program that can do lossless JPEG rotation is IrfanView (the quick access key is J).

Another way to resize an image in Photoshop, which will help when sizing a series of images uniformly, is to use the crop tool. Select the crop tool and then, below the main menu, input the dimensions and dpi you desire. Then, you can simply crop the image by selecting the entire canvas and pressing enter. This will automatically resize your image, plus, until you clear or change the parameters, your crop tool will perform the same exact function on any other images you are working with.

Also, one trick that works reasonably well for upsizing an image without losing significant resolution is to use the Image Size dialog box, shown above, and change your measurement to percentage. Then, upsize the image to 110%. If you do this several times, you will notice that the resolution of the now larger image remains surprisingly consistent. I have used this and it works, however, no one seems to be able to explain why. Use 109% or 111% and it doesn’t work nearly as well... 110 seems to be a magic number in Photoshop. In fact, the book, Photoshop for Digital Photographers claims that you can upsize a thumbnail to a poster without ruing the image. I’m not sure you can take this trick that far, but it does work for at least doubling the size of an image, or making a web image of hi-enough resolution for printing.

jb

I'm not so sure about the dpi, and I would be glad to hear what people here say about my view.

IMHO: out of my workflow and considerations comes the one and only file that contains all the information available to me, as TIFF, or PNG at about half the size. For web use, no question that I have to resample it to the intended ppi screen size. But for printing, why worry? I feel that it would be best to leave it entirely to the designers of the driver, ie. printer. They have to put up with all sorts of files. If I pick some dpi by guesswork, the driver will have to re-process it either way all over again, with suboptimal results. My advantage of "no dpi" would be that I have the one and only original file ready for all imaginable purposes.

You see what I mean. Comments?

"Note that there are some programs which create JPEG files which the photo.net software for attached images doesn't understand. If you attach such an image to a forum post it will display as a link, not as an image, even if it's under 511 pixels wide. One program known to do this is Micrografx Picture Publisher 8.0. There may well be others."

There are - Picture Window Pro is one of them. It took me some time to figure out, but now I use PS Elements to resize on those rare occasions when I need to include in-line attachments.

There have been several threads on photo.net about this, but it is good to have a single article which clarifies much of the confusion surrounding pixels and image size.

The concept that increasing size by increments of 110% has been raised before, but there is by no means agreement that it actually provides any benefit. See: Can enlarge w- Photoshop 110% with great results (http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=005d5j).

I agree that the difference using lots of small increments vs. one big increment makes very little difference in most cases. I've seen all sorts of "tricks" suggested. For example I've seen statements, as above, that upsizing by 110% is "magic" and 109% and 111% don't work as well.

I'm not sure I believe most of these statements. My own experience suggest that the program you use and the algorithm you pick makes significantly more difference than the step size you use.

There's certainly an advantage in using bicubic over linear interpolation for photographic images for example. Going to an algorithm like Lanczos can improve things a little, but really all of the upsizing algorithms have problems. If the information isn't there in the first place, it's essentially impossible to accurately recreate it.

Genuine fractals is works in a somewhat different way. Sometimes it works, sometimes it creates something that looks more like a watercolor painting than a photograph when you look closely at an image.

The bottom line is that there is no single "best" (or least worse)solution for upsizing images.

This thread has answered a lot of my questions about re-sizing (I'm new to digital imaging). Could someone tell me what happens to the original image when you re-size? Is it preserved ?, does the re-sized file ask for a new name? Can I always go back to the original large (maybe RAW) file for same image quality even if I've altered it from re-sizing and other changes? Please give examples, they help a lot. I currently use Elements but will soon be getting PS. Thanks, Bob.

I've tried Irfranview for resize images but my experience is color loss specially when going from 1800 to 768 or 192 pixels. I' ve got better results using Photoshop 6.0 and taking advantage of automated tools (batch and scripting) and saving images as web. In this link is La Papa

On Robert Nancarrow’s question about saving your resized image: you can always revert to your raw image, but you will have to reapply any processing parameters you used to make the tiff or jpg. Raw files are your “negatives.” You cannot save changes to them; you can only export a copy with the applied changes in a different file format. The Raw file itself will not be changed.

When you resize or make any other alterations to an image in Photoshop (or another program) it’s advisable to save those changes under a new file name. Once you overwrite a file with new information, your old info is gone (or at least very difficult to recover). In other words, if I am in Photoshop working on a file called abc.jpg and I increase its size by 200 percent then save it, abc.jpg will always appear 200 percent larger than it was before the changes were made. So, when I know that I am about to alter an image, I’ll resave it with a different name – in this example, I would save it as “abc_2.jpg.” (I usually “Save As,” before I do anything else, because otherwise you run the risk of hitting “Save” by accident and overwriting the original). Then, only when I am sure that the original is less desirable than the new version, will I permanently delete or alter a file.

Hope that helps

jb

A couple of things. first PPI: Many browsers only understand 72ppi images, they will balk at all other resolutions and the image won't display, so if you are formatting for the web it is best to assume that at least some people won't be able to view other resolutions and save as 72ppi, Second Photoshop: Use save for web under the file menu if saving in photoshop 7.0 or better and intending to post to a web site, that automatically formats for 72ppi. The other reason for doing this is simply that photoshop puts extra info in the XML meta info for jpg images, save for web doesn't do that and many browsers balk at the extra info. I just tried the 110% and managed to get an image up to almost double, after that it was unusable.

As far as I know most, if not all, browsers and operating systems ignore the dpi setting, so whether it's set at 7 dpi, 72dpi or 720 dpi - or even 7200dpi - makes absolutely no difference at all.

Thank God that the author puts to rest this silly 72dpi figure that people bandy about, not realizing that for screen viewing, it makes no difference. The scan tips web site also makes this clear. Thank you for making this clear...

First time that I ever understood to some extent what these terms mean.

I'm late to the party on this, but thought I should add an observation I made a few weeks ago. When dropping images into a MS Outlook message, they appeared larger (and fuzzier) on the screen than they had in Photoshop Elements. In this case, the DPI setting did make a difference (I realize Outlook isn't exactly "web", but many people might assume it is). Elements defaulted to 72 DPI, but Outlook wants to see images at 96 DPI in order to maintain the same size. Changing the DPI to 96 before resizing the original images gave me the results I was looking for.

The other parameter that is affected by DPI in Photoshop is the size of any text you add to the image. It seems that the text size in points is tied in to DPI setting for the image. I imagine that once you save the image, everything is locked together,and the relative size of the text can't change.