The Free ExtraTiff Windows 32-bit Photoshop-compatible plugin and ExtraTiff Windows 64-bit Photoshop-compatible plugin extend the ability of Photoshop to include composite 1, 2, and 4 bit/pixel, CMYK+Spots/Alphas, PhotoInk, Hex, and CMYKOGV TIFF formats, commonly used for halftoning in the Graphic Arts industry. v9.44 and later include support for selecting an image from TIFFs with multiple IFDs. (Click the appropriate link and choose "Extract", "Open With", or “Save Link As...” to save the plugin to your computer) They work with all 32/64-bit Windows Photoshop versions from 6.0 to CS2022. The Win32 version cannot support BigTIFF format > ~3Bn pixels x colors.

Installation consists of nothing more than downloading the plugin .ZIP file, extracting ExtraTiff.8bi and adding it to a folder. This will usually be something like :
C:\Program Files\Adobe\Adobe Photoshop CS\Plug-Ins\File Formats
or
C:\Program Files (x86)\Adobe\Adobe Photoshop CS\Plug-Ins\File Formats

You can check the path on your system by going through the Start menu as if you were going to run Photoshop, but instead of left-clicking it, use the right mouse button, and choose Properties from the popup menu. The "Start In" section tells you where to look for the Plug-ins\File Formats folder. Once you've added ExtraTiff.8bi, to the correct folder, Photoshop's File/Open As... dialog will include the ExtraTiff option.
Note that the current version 10.04 does not create thumbnails for large images,
because it proved to be too time-consuming when using File.. open.

Thanks are due (in no particular order) to the following, who have all contributed to the free source files used in the creation of this plugin. None of them have endorsed my work, nor are they are in any way responsible for any use or misuse I have made of their generosity :