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I have been ask to make a newsletter e-mailable. I tried to reduce the photos to reduce the files size, but it was still too big. I have tiff photos. In the printable version the photos are at 400 dpi. How low can I go on the dpi and still have them visually look good in a pdf to be sent in an emailed?

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  • I tried reducing all the photographs to 200 dpi and it was still too big. Should I try 72 dpi on all my tiff photographs? – David Feb 2 '17 at 0:10
  • You'd save a heck of a lot more space by converting them to .jpg too. Unless you're expecting your newsletter readers to actually print the pdfs, 72 dpi is 'screen resolution' for all but newer 4k screens & retinas. – Tetsujin Feb 2 '17 at 8:01
  • @David Changing dpi won't change anything with regard to file size. You've got to reduce the number of pixels to do that. It doesn't matter if you're set to 1 dpi or 10,000 dpi, a 3000 pixel by 2000 pixel image will be 6 MP. – Michael C Feb 2 '17 at 11:32
  • @David Please see the suggested duplicate. It fully explains your issue. – Michael C Feb 2 '17 at 11:33
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DPI is meaningless in an electronic image, it's a print specific value, see What does DPI mean?

In an electronic image, DPI is just metadata, a "hint" for the print. Specifically, changing that value has no effect on file size, only representation on paper or in a WYSIWYG page editing software.

What you care for for an email newsletter or website are the pixel dimensions (width x height) of the images. You have to decide how big it should look on a typical screen (eg. 1920x1080) and choose a size appropriate for that.

The smaller your image in pixels, the smaller the resulting file, at equal compression.

You can further reduce the file size by increasing compression, or converting to a different format (jpg), but how much compression is acceptable can only be judged visually for your specific images.

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  • When imported into a word processing or page setting application dpi can have meaning. The OP hasn't told us how he is creating the newsletter with embedded images. Please see Is there any practical difference between saving at 300ppi or 72ppi? for a fuller explanation. – Michael C Feb 2 '17 at 11:36
  • @MichaelClark: the question was about file size. dpi won't affect that. also, in a word processor dpi is also only a hint, you can always resize the image on the page. – ths Feb 2 '17 at 12:41
  • Dpi is more than a "hint" for such applications. It determines the default display size from within those applications until the user does something to alter the display size. As such, the dpi does have meaning. When the display size is altered by the user, that change is saved internally by the app by altering the instruction for the dpi at which the image should be displayed. – Michael C Feb 2 '17 at 12:50
  • @MichaelClark you seem to have a different definition of hint than I. I'd say the app sets the default according to the hint. Also, that an app changes the dpi of an image when resizing is an assumption i cannot follow. I just tried with ms word and saved a resized tiff from a doc, and the dpi was the same as before. what word does internally is opaque and thus irrelevant. – ths Feb 2 '17 at 12:55
  • But what it does internally is tell itself to ignore the dpi in the image file and use a dpi of xxx instead. – Michael C Feb 2 '17 at 13:02

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