How does the TIFF format compress images?

Question

When we choose "File> Save As" to save an image to a TIFF file, a TIFF Options dialogue box appears with 4 image compression options( None, LZW, Zip, Jpeg). What is this for? Does the TIFF format compress images? Are they destructive to the image quality? THANK YOU

Answer 1

If you select no compression, it will take up too much space, guaranteed.  TIFF lets you pick any compression method supported by your program and the viewing program.  Some are lossy, some are lossless.  Most TIFFs tend to be compressed in LZW or ZIP, both of which are lossless.  You can also choose to compress your TIFF using JPEG compression, which is lossy, but I can't imagine why you would do this instead of simply saving as a JPEG file, which is more likely to be properly opened in browsers than a JPEG-compressed TIFF file.
And in response to one of the previous posts, not all compression throws away details from your file.  Only lossy compression (e.g., JPEG, or in the music area MP3) throws away data.  The lossless compression techniques simply encode the data in fewer bits if possible.  (One important fact not relevant to the web, where you will use 8-bit-per-channel files:  If your photos are 16-bit-per-channel, don't save in LZW compressed format; they will actually become larger than the uncompressed image.)  For a simplified example, if there is a series of 16 pixels of solid white, a losslessly compressed image will have code that says, in effect, 16 pixels of (255,255,255) using an abbreviated code instead of simply listing (255,255,255) sixteen times.  It builds up a directory of byte combinations and can use just a few bytes to refer to many bytes of image data.  Because the coding and decoding is exact, there is no change in the image data when it's opened.
JPEG is a lossy compression technique that doesn't actually record pixel values at all.  It uses formulas to specify averages and changes within regions.  In effect, it records the fact that a given group of pixels has values centered on X color, and that the upper left is much pinker and the lower right is much greener than the average.  When you pick the degree of quality for JPEG compression, you tell it how small to make the comparison cells.  As you can imagine, if the image has text, tree branches, or other highly contrasty subject matter, this will cause serious weirdness if the comparison cells aren't very small (i.e., you don't have the quality set to max).