I have a number of digital photo files in jpeg format, and want to downsize them from their current size of about 410 K to about 100 K, as the web page I am posting to is not able to take such large files. How do I go about doing this?
I am running Windows XP and have Adobe Photoshop.
Your help is appreciated.
Shrink 'em. That is, scale them down to a smaller size. Fewer dots, fewer K.
Increase the compression.
Save them “web ready” (without a thumbnail/preview). Those previews waste more space than you might think.
Or, mix ‘n’ match from the above.
Some apps will flat-out ask you when you save if you want to “Compress file size to ___”. GraphicConverter for Macintosh is one of these.
Change the resolution to 72 pixels per inch - that should be enough for the web, and should drastically reduce file size
Availl yourself of the following:
-Printer
-Scanner
-Scissors
Print out your images, then, using the scissors (exact-o blades are ok too) trim your picture. You can then scan your trimmed-images back into your computer and, lo and behold! you have smaller jpegs.
Alternatively, assuming you’re using a newer version of photoshop, you can simply select “save for web” from the file menu. You can easily adjust the compression rate and the interface will display the size after conversion.
If only there were a computer program that would let you do such a thing in a single step. You’d think it would be cropping up all over. 
Download Irfanview from Irfanview.com. It’s a free image converter that will allow you to open a JPEG then save it with higher compression.
A selection of free online image crunching tools is also available via Google.
I have a question about .jpgs in Photoshop, now that you mention it.
Every time I save a .jpg in Photoshop, by default it checks a box called “Save as Thumbnail.” So where the heck do all these thumbnails go after saving? I’ve never seen one.
Also, why do some people write uppercase file extensions for .JPG and .GIF while other use lowercase? Which is better? I’ve noticed that sometimes if your HTML is calling for a file with an uppercase file extension and you have saved it with lowercase, or vice versa, it won’t display. Who thought of this kloodge?
Resizing/recompressing existing jpegs can sometimes lead to unacceptable loss of detail - wherever possible (and especially with images you’re creating for yourself), work on the file in a non-lossy format (.bmp or .tif, for example), do all of your resizing/resampling/cropping, then save as a compressed jpg at the last minute.
Of course this isn’t always possible - many digital cameras store the images internally as jpegs now.
Since the OP specifies that he/she has Photoshop available, there’s no need to download any extra tools (free though they may be!). First, you can use the crop tool to cut down the image. This would be the best first step if the image shows more than you need it to. Otherwise, skip ahead to using the Image Size function. In recent versions on Photoshop, this is in the “Image” pulldown menu. Here you can adjust the number of pixels in the image. Fewer pixels means a smaller file sizen (compression aside). Last, you can use ‘Save for Web’ to save the file to a lower quality compression level to further decrease the size.
Sorry, but resolution on its own has no bearing on filesize whatsoever. Resolution is a relation between two quantities, in this case pixels and inches. Resolution alone doesn’t tell you anything, you have to know at least one of the other quantities.
Imagine if you asked someone how long a particular drive took them to complete, and they answered “55 miles per hour”. Did that answer your question? Obviously, you’d also have to know what the distance of the trip were to figure out the time it took. It’s the same with resolution. For 72 ppi to be meaningful in terms on file size, you’ve also got to know what the image size in inches is. Is that 72ppi at 3’x5’ or is it 72ppi at 8’x10’? A file that is 72 ppi at 8’x10’ will contain many more pixels and be a larger file.
But in fact, web browsers don’t care about image resolution at all. When you go into Photoshop’s Image Size tool, you can specify pixel size, real size, or resolution. All that matters on the web is the actual pixel dimensions, so there’s no math required. Make sure that the “Resample” and “Constrain Proportions” boxes are checked. Then just input a smaller pixel number for either height or width and click the “OK” button and you’ll be in business.
If you want to see the relationship between resolution and print size, uncheck the “Resample” box. You’ll notice that you can no longer change the pixel dimensions, because the resolution will only effect how large the file will print.
The thumbnail actually gets saved as part of the file itself. This will (very) slightly increase the file size too. I always leave that box checked unless i’m working with web graphics. Even then, it doesn’t make a huge difference, but every little bit counts to those using a modem!
HTML is case-insensitive. To an HTML document, picture.jpg and picture.JPG are the same file.
JavaScript, on the other hand, is case-sensitive, which means that picture.jpg and picture.JPG are interpreted as two different files. I’ve banged my head on a wall for hours trying to find out what was wrong with a simple mouseover - it was the capitalization in the file extension.
For this reason, you should always be consistent to avoid mix-ups like this.
Enigma42 - when I scan a pic, it asks me both for the size and the resolution. The lower the resolution, the lower the file size. So, if I’m scanning stuff for the web, I use 72 dpi and that definitely produces an image whose filesize is much lower than if I had scanned at 300 dpi. Question is, how does dpi convert to ppi - or am I talking apples and oranges here?
Am totally non-technical - all I know I picked up only when I absolutely needed to know - so please forgive any non-understanding of basics, and as we have a habit of saying here - “please kindly explain” 
This is not a “kloodge.” This is the proper operation of an Operating system that distinguishes between upper and lower case in file names. Windows (and DOS before it) do not distinguish between upper and lower and lower case - they treat “FILENAME.EXT” the same as “filename.ext” Unix type systems do distinguish upper and lower case - “FILENAME.EXT” is not the same as “filename.ext” It is completely with in the standards to have filenames that vary only in the capitalization.
You normally get into trouble when you create html stuff using some Windows software and transfer the completed stuff to a Unix type web server. The windows software has no trouble finding your files with mixed up capitalization (because they look the same to Windows,) but the webserver can’t find it because your mixed up capitalization looks likes different files to the operating system.
Simplest is to always use lowercase for the whole filename and the extension - you’ll never have trouble if you always name your files by a simple rule.
This is not a design flaw or bug in Unix. It is simply the designed-in filenaming convention.
Windows (and DOS) actually have to do a little jumping through hoops to be able to ignore upper and lower case differences. They first must convert the filenames to all upper case when comparing filenames. This is a bit of a historical hang over from the first days of DOS. Way back then, some home computers only had uppercase - the IBM PC had upper and lower case, but not all others did.
When you do a scan, you select an area in the preview - basically telling the scan software “start here and make a scan X inches by Y inches.” Then you specify the scan resolution. X inches at 72 dots per inch by Y inches at 72 dots per inch. If you change the resolution here, you change how many dots the scanner reads per inch, and you do get files of different sizes.
When you already have the image, changing the dpi doesn’t change the number of dots you’ve already got. For most programs, the dpi information is only used when they go to print to set the size it should come out on paper. Think of it as using a magnifying glass - a smaller dpi number gives you a bigger image (magnifying) and a larger number gives you a smaller image (shrinking.)
For most programs, you’ll need to use something like “scale image” to actually change the number of pixels in the image. This will actually eliminate pixels to make the image smaller - or interpolate (mathematically create) pixels to make the image larger.
Some programs don’t wotk this way, though. Some of them will actually scale the image when you change the DPI setting.
I don’t use Photoshop, so I can’t tell you what it does. From the one or two times I have used it in the past, I only remember it being a pain to actually get it to do what I wanted.
I’m used to the GIMP, and it gives you both options in one window - scale image and change DPI. Since it also shows you the finished print sizes, file sizes, and pixel numbers as you change things it is pretty clear what does what.
I, personally, always use lowercase file extensions. I mean, why on earth would I even want to use uppercase?
But for no intelligible reason, Photoshop ( <–idiot) defaults uppercase file extensions. I have to manually retype them in lowercase.
Urk.
Some image programs save it that way by default. Pain in the ass.
In Photoshop, do the “Save for web” option. It gives you a lot of parameters to tweak, and the resulting file sizes are TINY.
Irfanview is very neat, but won’t do tiny file sizes like Adobe Photoshop can.
Tip for people that don’t have Adobe: never use MS Photo Editor to reduce a file’s size in terms of dimension. It always makes them totally distorted. Use MS Photo Editor to touch up and fiddle around by all means, but then reduce the size useing Irfanview.
This is simply untrue, however, the majority of web servers on the market are configured to interpret URLs (in general) and file extensions (in specific) as case insensitive.
In so far as the whole DPI debate is concerned, changing resolution by itself (as mentioned already) will not affect your file size. If you decrease your resolution though, you will notice that the dimensions of your file get larger. So, if you decrease resolution while maintaining the same dimensions, you will reduce filesize.
Other things you can do:
-Crop your image to trim off dead space.
-Save your image with a more agressive compression setting.
-Save your image with no preview.
-Try saving your image in a different file format. (jpgs are good for photographic images, gifs are good for line art or images with large blocks of flat color)
If your images are ~400k, then I’m guessing they are fairly large, so your best bet would be to reduce the dimensions and scale back the resolution to 72dpi. That should bring you down to 100k without too much difficulty provided you are using a compression setting of 7-9. As was already mentioned, use photoshop’s “Save for the web” (Ctrl + Alt + Shift + S) and play around until you get the size, compression, filesize and image quality you want.