Color Temperature Blue (alternatively, Correct to Blue). A range of color correction filters used to raise a source's color temperature. Available from all four major gel manufacturers and also available in dichroic filters. Full CTB will convert 3200K to 5700K 1/2 CTB will convert 3200K to 4300K 1/4 CTB will convert 3200K to 3600K 1/8 CTB will convert 3200K to 3300K Some also offer 1/3, 2/3, and 3/4 varieties. For more, see the links and attachments to the wiki entry color temperature . Note that not all manufacturers' products are exactly equivalent.