How to determine and/or change the color depth of a file

[arti...@adobeforums.com]

Am new to using Illustrator CS3.

I'd like to upload some image files to an online digital printing company. They specify that image files should be sRGB, and should be JPG or TIFF. Okay, I figured out how to export my sRGB files as TIFF files.

This company also specifies that image files should be 8-bit, not 16-bit.

Dumb question: How do I determine if my images are 8-bit? If they aren't, how do I change them to 8-bit?

I gather that 8-bit refers to "color depth," but beyond that, I'm lost. Thanks for any help.

[Scott Falkner]

TIFF and JPEG images exported from Illustrator are 8-bit. You can open such images in Photoshop and look at the image's title bar.

[arti...@adobeforums.com]

Very helpful, Scott. Thanks.

I don't have easy access to Photoshop.

Scott or anyone, is there any way to verify within Illustrator how many bits of color-depth an image has?

And are the designations of 8-bit, 16-bit, etc., something that apply only or mainly to raster images, and not to vector?

Thanks.

[Scott Falkner]

bit depth refers to the amount of information in a pixel in raster data. Illustrator files can contain raster data, but I believe Illustrator does not support 16-bit images.

Generally it is not something worth worrying about. 16-bit is usually used only for scanning or raw digital imaging. The 16-bit raw image is opened in Photoshop, edited, and converted to the appropriate device profile (usually from RGB to press-specific CMYK) then reduced to 8-bit. Since all edits tend to destroy information and gradually limit the palette in the image, the more data one starts with, the better the image retains the colour information wanted.

8-bit images contain 256 values (2^8) for each RGB component of each pixel. 256^3 = 16,777,216 possible colours. 16 bit images have a spectrum of 281,462,092,005,375. That's 281 million million and change.

[Scott Falkner]

Back up a bit. What type of file are you sending the printer? You should be using PDF. If they won't accept PDF hang up the phone and never call them again.

[arti...@adobeforums.com]

<What type of file are you sending the printer? You should be using PDF.>

Please elaborate. Thanks for your help, Scott.

[Scott Falkner]

File > Save As. Choose PDF. If the following dialogue choose Press Ready.

Biting my tongue.