Possible to set dpi for PNGs?

[Byron S.]

Is it possible to set the dpi that the PNGs are saved in, either when created in Impict or when converted from BMPs by H&M?

I reduce many of my screenshots by 75% in TNT. They look fine onscreen but when printed they are fuzzy. I have a hunch that setting the PNGs to be saved at 150+ dpi would make them sharper when printed. If so, this would save a tremendous amount of time authoring the help system since I wouldn't have to create two versions of each image; a reduced size image for online, and an original size image for print (as described in postings elsewhere in these H&M forums).

Thanks.

[Tim Green]

Byron,

To the best of my knowledge the dpi setting is simply an information tag that tells programs and devices how to interpret the image, it has no effect on their actual physical resolution. That's why you can change the dpi in Photoshop or Paintshop without doing any image conversion.

So if you were to change the dpi setting it would actually have no effect at all on your printout. In fact, the result would probably be that the images would print out at half size, because you would effectively be telling the printer to print 150 native pixels of the image in one inch. What is happening at the moment is that you are printing 72-75 native pixels of the image in one inch at a 150 dpi resolution, which means that the image is being scaled on the fly for printing, hence the fuzziness.

The bottom line is, if you want full-quality printouts at full size you need an image with a genuinely higher physical resolution, i.e. with more native pixels in it. No free lunch, unfortunately...

[Alexander Halser]

I have a hunch that setting the PNGs to be saved at 150+ dpi would make them sharper when printed

Wouldn't make any difference. Help & Manual, Impict and TNT save PNG images with 96 dpi which represents screen resolution. A printer should appropriately scale the image, but if you reduced the size before, it of course has less details than the original image.

You could do the opposite way and let Help & Manual reduce the screen shot for online help. So you would insert the full size pictures (and get a good print quality) and when you create HTML or HTML Help, Help & Manual ensures that the screen shots do not exceed a particular size. You can set this maximum width and height in Project | Properties -> HTML Layout -> Images. This is a global setting, of course and applies to screenshots only, that exceed this size.