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Picture Perfect Checklist

The following is a checklist to to help send the smallest possible pictures to a mailing list (yet still good enough quality for viewing on a computer screen), with some of the reasoning behind each item.

Note that when discussing "size" of images, this can mean one of two things. First is the actual dimensions of the image in pixels (dots on the screen), and second is the size of the electronic file that is generated when the image is saved. The second, the filesize, is influenced by the first, the size of the image in pixels, as well as the number of colours (variable from 2 to 256 when saving as a gif), the file type (is it a gif or a jpg, or some other format, most of which can't be seen by everyone on the net as gifs and jpgs are), and the compression ratio (variable factor when saving as a jpg).


1. check resolution
If you'll want to keep a copy of the file to print, save with as high a resolution as your scanner or printer (the lower resolution of the two, if different) will go. If you're only going to use the photo to view on-screen, then 72 dpi is plenty, since computer monitors don't usually display any higher resolution than 72 dpi.
2. check colour format
Most scanner software will let you scan in any of several colour modes: 2-colour (line drawing - black and white), greyscale, 8-bit (256-colour) or 24-bit (16 million-colour), among other options. Using the most appropriate one for your image will result in a cleaner (less smudging) look and smaller file.
3. check alignment
Is the image straight? Less editing (rotating) will be required if it is.
4. crop scan area
Most scanner software allows you to select rectangular areas (with the mouse) in the "Preview" step so that the file resulting from the scan doesn't include huge white areas or unwanted background areas.
save a backup file (as 24-bit .tiff, or in Adobe (.psd) or Corel (.cpt) formats if using those programs)
... just in case. It's good to have on hand if you want to try different things with the image.


CROP out unneeded background areas
Do this before re-sizing, so that you don't have to shrink down the main areas of the image too much (if this is going to be necessary at all). Select the area you wish to keep (using a rectangular selection tool), then look for the CROP command under the "Image" or "Edit" menu, and click.
RESIZE (unless it's a line drawing) to fit inside 620 (width) X 310 (height) PIXELS rectangle
In some software, this is called RESAMPLE. The reason for these dimensions is that many computers are sold with their monitors set to 640 X 480 resolution. This can be changed with most modern monitors and video cards, but many people don't bother or don't know how. This monitor resolution is the dimensions of the screen in the number of pixels of width and height. With a browser or other software open to view the images, even maximized to fill the screen, the window available for image viewing is restricted by the space taken up by the title and menu bars, scroll bars, etc. Any image larger than about 620 X 310 will most likely not fit into everyone's viewing window in its entirety.
FIDDLE with sharpness, colours, whatever else might be needed (there's always "UNDO" under "Edit")
This part is fun ... explore your menus to see what you can do.


check resolution
If saving a copy to send via email, make sure it's only at 72 dpi. If you want a copy to use for printing, save it first (under a different name, and as a .tiff or .psd or .cpt file) at the highest resolution you can get.
determine type of file
Photographs are always better saved as .jpgs. Paintings and art with a lot of gradient colours as well. Line drawings and cartoon-like images with a lot of solid colour areas make smaller, cleaner files saved as .gifs. Here are a couple of examples.
if .gif, determine bit-depth (number of colours) to save.
You are limited to 256 colours or less. Black-and-white line drawings should be 1-bit (2-colour mode) before saving as a .gif. If it was scanned as greyscale or full colour and you try to change to 2 colours, you may lose some detail, so 2-bit (4 colours), 3-bit (8 colours), or 4-bit (16 colours) is a good compromise. For cartoon-like images, 16 or 32 colours are often a good choice, unless you're sure there are fewer than that in the image. You actually have a choice (in most software) of any number of colours between 2 and 256. The fewer colours you set the image to, the smaller the resulting file will be. A 2-colour line-drawing gif can end up under 10 Kb in size! Experiment a little ... convert the image to a different bit-depth and study it. If you don't like it, you can click on Edit-Undo and try again.
if .jpg, set compression level
You can safely compress most images up to 45 or 50 percent without losing too much quality when viewed on screen, as long as you do it only once. Leave that compressed save until after the very final edit ... use other formats or uncompressed .jpg format for backups. Keep a backup (or your original scanned file) in that other format for future editing. An image that fits the pixel dimensions above can easily be made smaller than 30 Kb.

For those who are new to computers and electronic files: On a Windows PC, you can see your file size if you get familiar with Windows Explorer (Start menu under Programs), and view your file listings in "Detail" mode rather than "Large Icons." You can also see file details from the "Open" or "Save As... " dialog boxes ... there is a button at the top of the screen that enables you to change your view mode. This view gives you the name of the file, the date it was last saved, and the size in Kb.

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