Question from Dave: I have pictures in iPhoto that I want to reduce in size without losing the clarity or any of the picture. How do I do that?
Jason answers: If you want your digital photos to be smaller in file size so that you can email them or have them take up less space on your hard drive, you have to lose information in the image to make them smaller. There is no getting around this.
I assume that your photos are JPEGs. JPEGs are already “compressed”. This means that when the picture was taken, an algorithm was run on the picture to remove information that shouldn’t be recognized by the human eye. Depending on what quality you want, the algorithm will remove or keep more data. When you take real life photos, there are millions of colors that can be described by the computer. Some of these colors are very close and by taking close color values and making them the same value, you make a smaller file without losing clarity since less information is needed to describe all the colors in the photo.
In summary, you can reduce the file size of your photos by opening them up in a photo editing program like Photoshop or even Preview and resaving them as a lower quality JPEG until you get an acceptable image. It is a trial and error thing. In iPhoto, if you select File->Export, then you can choose a Low, Medium, High or Maximum quality image. If you open the file with Preview and choose File->Save As JPEG, you will get a little slider to go from least to best.