Image Size Box:
This is the Image Size box in PhotoShop. You will find some version of it in most image editing programs. Here is a brief description of what the sections mean:
Document Size refers to how big the image will print. If you are doing pictures for the web, you can ignore this.
Resolution. This is the box where you make that change.
Whether or not Resample is checked makes a big difference in what happens to the file.When it is off, the total number of pixels in the image remains unchanged (the Pixel Dimensions area at the top is grayed out).
So, resizing with Resample turned off means that the Resolution (pixels per inch) is affected when you change the image dimensions (inches). The total number of pixels in the image remains unchanged, so therefore, if you change the number of inches, it’s going to change the number of pixels per inch - since they have to be redivided among a new number of inches.
This is useful in dealing with an image from a digital camera that has large dimensions but is only 72ppi. Changing the Resolution to 300dpi (for printing purposes) without Resample turned on, will result in a reasonable sized photograph because the total number of pixels in the image is now divided by 300 instead of 72 which results in fewer inches. (You think this is confusing, you should see what I’m not telling you!)
Sometimes, this seesaw effect will not give you the size you want at the right Resolution. That is when you need to turn Resample on, and the software will add or subtract pixels to force it to fit. It tries to guess at the right color for these pixels based on the ones around it, and it does a pretty good job. There is some image degradation, but nothing you’re going to notice unless you are preparing graphics for high end printing.
Now, with this rudimentary understanding of what is going on, here is a rule-of-thumb reference for doing what you will most likely want to do without having to think about why you are doing it. We suggest you print this page and keep it near your computer.
When you download graphics from the web, you are pretty much stuck with what you get. Web files are purposefully made small and light so they will load quickly. The image will look fine onscreen, but enlarging it or printing it out will have very disappointing results. The good news is that when your own art is on the web at 72ppi, no one else can just take it and do greeting cards or t-shirts with it, because the image quality just won’t cut the mustard.
If you will change or edit these files or work with them in any way, and they are in JPEG format, change their format to TIFF. Leaving them as JPEG files means that every time you save a change, you throw away pixels from the file (more about that next time).
Graphics from a Digital Camera:
For Printing: You will want to change to resolution from72ppi to 300ppi. Uncheck Resample and change the Resolution to 300dpi. See what that does to your print size dimensions. If they are a size you can work with, you’re all set. If not, turn Resample on and set the dimensions as you want them, leaving the Resolution at 300ppi. Save the file as a TIFF.
For the Web: (See Below)
Graphics from your Scanner:
Photographs and Paintings: Scan them at 300dpi (that’s the term the scanner will use). If your scanning software has a choice of percents that you can scan at, choose one close to the final size you will want to use. For example, if you are scanning art that’s as big as the scanning bed and you only want to use it on greeting cards, scan at 50% or 25%. Conversely, if you are scanning something small which you want to use bigger, this is the time to enlarge it for best quality. You can resize in the computer but it’s better to do it as the piece is scanned.
Line Art: Many scanners will have a setting for Line Art which you should choose. Then scan at 600dpi. Line art needs a higher resolution to smooth the edges - since they are not blended into any other color.
If you need *really* clean line art, like for making rubber stamp plates etc., scan at 200% at 600dpi. Do all your clean-up on that file and then change the Resolution to 300dpi (with Resample turned off) which should give you a very clean file at the right size.
Graphics for the Web:
Web graphics have to be lean and mean for speed. The maximum resolution for browser display is 72ppi, so anything more is overkill that costs you in file size. The smaller the file size, the better, so keeping the width under 400 pixels is a good rule of thumb.
When your graphic is ready to be made “web-ready”, do this. With your source file open and any changes saved, select Image Size from the Image menu, and, with Resample turned on, *first* change the Resolution to 72ppi, then see what the pixel dimensions have changed to. Change the width to something reasonable below 400 pixels and notice that the height changes automatically, because you have Constrain Proportions checked. Click OK.
Your image is probably smaller on the screen. Choose Actual Pixels under the view menu to see what the image will actually look like on the web. Then, choose Save For Web under the File menu. A preview window will open where you can still play with image quality. When you are satisfied that you have the best balance between image quality and file size, click OK and name and save the file. You will then be back at your source file. Be sure to close it *without* saving the changes you made to the resolution, so it will be all set for next time you need it.
If you are not using PhotoShop 6.0 or newer (or Elements) and your software does not have Save For Web, you can choose Save As and select JPEG or GIF as the file format.
