Even if you have not asked us to work on your images they may still appear differently in your review file from the way you sent them. This is because they will now have been properly prepared for commercial printing in the following ways:
Color conversion: Images produced in RGB (red, green, blue) format will be converted to CMYK (cyan, magenta, yellow, black). This will make colors appear darker, especially bright blues and greens. We will apply color management techniques to reduce the impact of the necessary conversion process.
Ink saturation: Dark images and solid backgrounds will be adjusted to reduce the ink saturation to within printing limits. If images are over-saturated then most printers will simply reject the files as ink will take too long to dry, show through the pages and cause paper to wrinkle.
Image enhancement: In order to ensure your images appear their best in print they may also have been lightened, enhanced or sharpened in Photoshop.