to Create Photos for E-Mailing and the Internet
INTRODUCTION: There are at least three different things involved. Even professional graphic artists and photographers get confused all the time, so I'll try to be as clear as I can. Here they are:
1.) Image size.
2.) File size.
3.) File type.
A photo has both an image size (how big it is on your screen, measured in pixels horizontally and vertically) and a file size (how much space it takes inside your computer's memory and how long it takes to download, measured in kB [kilobytes]). These are two very different things. These two sizes are only slightly related to each other, and they must both be correct. This is where 90% of the confusion lies.
Photos for e-mailing and the Internet must always be of a type called "JPEG," which are files that end in ".jpg" That's the easy part.
Here are the details:
Image size: Image size is absolute and measured in pixels. DPI (more at bottom of this page) has nothing to do with anything, so don't worry about it.
To fit most standard computer screens your photo should be not more than 400 pixels tall and not more than 750 pixels wide. Sure you can make it bigger, but most people will have to scroll around to see your photo, even if it fits on your screen. People like me have huge screens, but we must realize the most popular screen size today is only 800 x 600 pixels. Even people on huge screens usually keep their browser windows set to 800 pixels wide, even if we let them grow taller. When you consider all the borders to the sides and especially top and bottom, there are at best only 750 x 400 pixels left for our images.
Of course if you want to fit a couple of photos on a web page you have to make them smaller.
You usually set the image size in software like Photoshop, or in your digital camera under IMAGE SIZE.
If your digital camera has a 640 x 480 pixel mode just use that. If the image from your digital camera or scanner is bigger (most are) you will need a program like Photoshop to change the size of the image. Go to the image RESIZE command in whatever software you use and make sure RESAMPLE is checked (This will vary with the program.) Then set the height to 400 pixels. If your program reads inches and/or DPI, change the units to pixels.
If you send files straight from most cameras it will be way too big to fit anyone's screen, as well as take forever to download, unless you set the camera to 640 x 480 or smaller and the lowest QUALITY jpg setting.
Smaller images will load faster and allow you to put titles or whatever around them. Only really panoramic images will get anywhere near the 750 pixel wide limit; the 400 pixel tall limit is usually what limits you first. Most of the images in my galleries are 400 pixels tall. I add titles and navigation bars, so I probably ought to make them smaller, more like 350 pixels tall. The huge images I post are 750 pixels wide and however tall they wind up.
OK, if you are scanning from regular prints then it's perfectly OK to set your scanner to 100 or so DPI, since with a 4x6" print that will give 400 x 600 pixels. Just remember the important part is the 400 x 600 pixel result, and not the DPI setting which is just a way to get there.
Unlike paper prints that can be rotated from horizontal to vertical, computer screens are horizontal, period. Vertical photos on computers wind up with a lot of black on each side. You have to limit the long dimension of vertical photos so your friends don't have to scroll all over to see them.
Ignore the box in Photoshop on the bottom left of the image that can display another indication of image size. That is the file size of the image only while it is open inside of Photoshop. That number is used to help people ensure that they are not overloading their computer while working. It is not the size of your .jpg file, which is much smaller. (That's the reason for the .jpg format!)
File size: File size, measured in kiloBytes (kb) has nothing to do with how big the photo is on the screen. File size is how big the file is inside your computer and how much information needs to be transferred while e-mailing or uploading or downloading your photo.
The reason you care about this baloney is because it determines how long it takes your photos to download and upload. Bigger file sizes may look a little bit better, but take a lot longer to download. This is the hardest thing to understand for normal people since file sizes are usually hidden!
File size will vary all over the place, even for the same size image, depending on what is in the image and what level of quality you set when creating it. You only see file size when looking at detailed file listings in your computer, or sometimes in the process of saving the files in programs like Photoshop. It is this mysterious side that makes people wonder why some things take forever to download.
For all practical purposes, always try to keep your photos below 50 kB for Internet and e-mail. This takes about 15 seconds to download over the standard phone modems almost everyone has to use. You of course can make your files any size you want, and yes a 200 kb file may look a little bit better, but no one will wait for it to download. Make a good looking image of only 24 kB and it will load fast and your friends will love you.
Ideally make your files as small as you can so long as they still look OK.
The busier and more detailed the image, the more data you need to make it look OK. A silhouette of a bare tree filling the frame will need a bigger file size than a frame consisting of just blank sky.
For any image you vary this with the QUALITY control in whatever software or camera you are using.. I use Photoshop's "save for web" command, which you get to at FILE > SAVE FOR WEB. In a digital camera you choose this in the QUALITY settings.
Digital cameras usually just let you choose high, medium and low (or fine, normal and basic) for the QUALITY setting. They don't tell you the file size in bytes. If you intend to e-mail images right from your camera, set quality to LOW and image size to 640 x 480 (or 320 x 240).
If you intend to pull the images into Photoshop to play with them before sending use whatever settings you want in your camera or scanner. You worry about all this when you're all doe with your image.
In Photoshop's "save for web" (ImageReady) program, I find setting the quality to about 30 - 40 gives me what I need for e-mail. I set this to 80 if I'm hitting my friends with cable modems. If I "save as" in Photoshop and set file type to .jpg then I find a quality setting of about 0 - 2 (out of 10) is about right.
The "Save for Web" command is preferred over "Save As" because it strips off unnecessary data (like notes) to allow the smallest file size.
B/W images I get better results instead by
Always look at the preview or "optimized" image and play with the quality setting to make the quality as low as you can while keeping an OK looking photo. You will save your friends all sorts of time downloading!
If and only if you know your friend has a high-speed connection (cable, DSL or most big offices and libraries) and you have one, too, then (and only then) you may wish to turn up the quality knob and send as big a file as you want. The image size should still not be any bigger since their screen doesn't change, however you may turn up the quality knob and increase the file size and improve the image a little. The BIG images on my galleries are usually about 350 kb, unlike the regular ones that are about 40 kb
If you really want to get into this (you shouldn't bother), the cleaner an image you start with the smaller a file you can create. Starting with super clean images from 4x5" cameras actually lets you make cleaner and smaller JPGs. Starting with grainy or noisy images (from 35mm film or another .jpg file) will require more bits of file size for the same quality final image. Why? Simple: all the grain or noise requires bits to be sent which otherwise could be used for improving the image; with a clean image no bits are wasted encoding or transmitting noise.
File type: Always use "JPEG," which are file names that end in ".jpg"
Those of us on Mac always need to remember to have our file names end in ".jpg," otherwise our less fortunate friends on Windows PCs can't see them. Photoshop's ImageReady program does this automatically, although the "Save As" command may let you forget.
Never send .TIF, .PSD, .BMP. .ZIP, .SIT or any other file types. Other file types are fine for their intended uses, but are way too big for e-mail or the Internet and will either take forever to download, or may completely kill your e-mail systems because they make files ten to a hundred times bigger than the same exact image in .jpg format. The reason not to use compressed formats like .ZIP is because they are much more difficult or impossible to open on another computer, and also since .jpg files are already compressed any further attempts to compress them usually result in even bigger files sizes. Another reason not to send any other file types is because except for JPG you'll need an advanced program like Photoshop just to see them. If your recipient doesn't have as fancy a setup as you do, he may not be able to see it.
The only exception to the JPG rule is the GIF format. GIF is sometimes better for logos, text images and graphics [not photos] that are mostly just a couple of flat colors. If you have an image like that you may want to try GIF format and see if you can get a better image with a smaller file size. It's still not for photos. Just use JPG.
DPI (dots per inch) has nothing to do with the Internet. Pixels (the "dots" in DPI) are all that matter since there are no inches on the Internet. Forget about talking in DPI, it only confuses things since you'll always have to do division and multiplication whenever you mean to say anything about pixels. DPI only relates to scanning and printing on paper when you have film or paper that is measured in inches. Old-time printers and graphics people usually talk about DPI since they are so used to working with tangible media. If you intend the photos you email to be printable then by all means set the DPI in the IMAGE SIZE box in a program like Photoshop to 72 or 100.
America Online (AOL): This is a really messed up service for photos. Attempts to send or receive more than one photo at a time in an e-mail to or from someone on AOL often gets screwed up. Just send one photo at a time and you should be OK.
When sending more than one photo at a time from an AOL e-mail what actually gets sent is a compressed archive file (usually a .sit or .zip file). If the recipient does not have AOL they will have to be pretty sharp to figure out how to decompress the archive and look at your photos. I hate it when this happens. Not only that, but the size of the compressed file is usually larger than the sum of the individual jpg images, since jpgs are already compressed as small as they can be.
When someone on AOL gets a bunch of .jpgs in a single e-mail sometimes they can see them, sometimes not. Try it with each friend and see!