https://forums.adobe.com/people/Per+Berntsen wrote 1/ Why would I need to use Photoshop (Elements?) not Lightroom to downgrade to 8-bit? (also - will Lightroom handle dpi reduction?) Lightroom cannot convert a file from 16-bit to 8-bit, because it never changes the original. (the image you see on screen is a preview created by Lightroom) All the edits you do in Lightroom are parametric - i.e. they are written as text to the catalog, and they are applied to the preview, but not to the original. When you export a file, a copy of the file is created, and the edits you have done are applied to the new file, and in the export dialog you can resize the file, and also set the bit depth to 8-bit or 16.bit. So if you want to convert all your tiffs to 8-bit, the best way to do this is to use Photoshop. You can create an action to do this, including using LZW compression, and run the action on the folders with the tiffs. Like I said before, I would back up all the (16-bit) files first, and at least keep them until you are sure that there has been no problems with the conversion. Once you have converted, you can't convert back to 16-bit. (well you can, but it's pointless,since all the 16-bit info will be gone, and there will no improvement in quality) 2/ Is ZIP or LZW still the most effective lossless compression? (btw I confirm that LZW on 16 bit increases filsize!) ZIP is most effective with 16-bit, LZW is most effective with 8-bit. A few words about dpi and ppi. Dpi means dots per inch, and is used exclusively for printers. It describes how many ink dots the printer can print per inch. Ppi means pixels per inch, and is also used for printing, but it describes how many image pixels are used to print one inch. There is a relationship between pixel dimensions, printed dimension and ppi - if you want to print an 8 x 10" image at 300 ppi, you will need a certain number of pixels in the image. How many? 2400 x 3000, because 8x300 = 2400 and 10x300 = 3000. Ppi is also used to describe the resolution of a scanner (some people prefer to use spi - samples per inch - each sample becomes an image pixel). You know that your scanner has a resolution of 5400 ppi, and you can then calculate the pixel dimensions. You are scanning 35mm film, which is roughly 1 x 1½", and when you multiply the ppi with the dimensions, you get 5400 x 8100 pixels. If you were to print the full image at 300 ppi, the print size would be 18 (5400:300) by 27 (8100:300) inches. Good points, thankyou - and yes I get what you mean about dpi and ppi.
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