ICC profiles - never used what have I been missing?

Question

Up until now I have never used separate icc profiles but have had to download all new drivers from epson to run my scanner and printer on new Intel Mac OSX 10.6. therefore it has given me the option to download the profiles.
Any advise for using them, can you turn them off - will i never want to turn them off?
What do they do exactly?
I may sound daft to many but unless I ask I dont learn, many thanks in advance.

Answer 1

Good advice so far and it is good that you ask these questions.
You asked earlier about your Epson printouts matching a print shop. It helps to understand color management as a communication chain. In the case of images, this is an ideal workflow:
1. Digital image is captured in RAW
2. Photographer converts RAW data into an RGB image. The result is referred to as a source image. It should have an embedded RGB profile, for example Adobe RGB 1998. To see if it has an embedded profile, look at the document title in the window.  If you don't see # at the end, the image has a profile, which is good. If you do see #, you have a broken image, and it's up to you to get the derailed train back on track. If the image looks good to you (on a properly calibrated and profiled monitor) tagging an untagged image is an easy task. Edit: Assign Profile, and select your working RGB.
3. The source image gets converted to the printer's CMYK color space, also represented by an ICC profile. This should be supplied by the printer. You do have the option of leaving the image RGB and letting Quark do the conversion when you output. Quark color management is somewhat more complicated to setup than InDesign CM, let me know if you have questions.
4. To soft proof how the image will look on press, first calibrate and profile your monitor with the proper hardware and software. Then open the RGB image in Photoshop. View: Proof Setup: Custom, and select the CMYK profile supplied by the printer. The colors may shift some but that is to be expected, a CMYK color space is usually much smaller than most RGB color spaces.
5. To proof an image on your Epson that will closely match the press, you can calibrate and profile your Epson (best) or use the canned factory profile corresponding to the paper loaded in the Epson. This profile is actually an RGB profile (the printer is not RGB but the profile that describes it is). Open the RGB image. In the print dialog under Color Management, choose "Proof." Color Handling, "Photoshop Manages Colors." Printer profile, select the Epson profile. Proof Setup, select the CMYK profile supplied by printer. Check "Simulate Paper Color"
When you print, print Photoshop will perform two conversions behind the scenes. First your RGB image goes to the CMYK color space. Then the CMYK image is converted to the Epson profile using an Absolute Colorimetric rendering intent.
Unfortunately I don't believe Quark has the ability to perform two conversions on output. So if you need to proof a Quark page it's a matter of conversion to the printer's CMYK when you export the PDF. Then you can print the CMYK PDF to your Epson from Acrobat, using Acrobat Color Management and selecting the appropriate Epson profile.