How to save images for use in bloom

I wonder if someone could give me wisdom on the best way to save images for use in BLOOM?
Should they be tiff? png? jpeg? or does it depend how you’re going to use them?
Any other wisdom?


There are two considerations: size and quality.

Here are some facts:

  • TIFF is not viewable in browsers (including Bloom’s), so Bloom automatically converts it to PNG
  • PNG is “lossless”, so it’s never going to mean a reduction in quality. There are no “compression artifacts”.
  • JPG compression is “lossy” but that allows much more complex images per megabyte. JPG has a “quality” parameter that you can use to choose how lossy; at 100% quality, it is still lossy, but you might not notice. I normally find that I can drop the quality quite a bit before it becomes noticeable.
  • Knowledge of PNG vs JPG is so rare in Bloom’s user community that we have implemented some automatic conversions when it’s obvious that the image is in an inappropriate format:
    • Bloom converts jpg images that are a single color to png in order to use less memory and storage space. But it cannot restore the quality that was introduced by the inappropriate compression into jpeg.
    • Bloom converts photographs stored as pngs to jpegs, for the same reason.

Now back to your question, here are two rules of thumb:

  • When you use a scanner for something other than a photograph save as tiff or png. You can always go to jpg later; but once you use jpg, you are introducing compression artifacts, and you can’t undo those. So keep the originals for non-photographs in one of these lossless formats (tiff or png).
  • Use PNG for line art. Line art is pretty sensitive to compression artifacts, and png compresses it well. JPG will make the formerly crisp lines fuzzy.
  • Use JPG for photographs.
  • For color illustrations, it depends on the complexity. You can try both, zooming in to see the effects of various jpeg quality settings, while watching the size.
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Thank you so much. Very helpful!

The line drawings are in jpg format. How would I change them to png formats? Is there a way to make the files less heavy so that they don’t bog down the Bloom program?

To get back to a lossless png, you would need to make new originals, either from the original digital source, or by re-scanning the physical images as tiff or png.
If that is not possible, Bloom’s handling/converting your jpg to png should suffice. If you wanted to experiment, pretty much any image program would be able to “Save As” png from the jpg files, but I doubt it would make any difference to Bloom.

As I stated in your other post, we don’t expect image format to have noticeable implications for performance while using Bloom. If you would like us to look into why you may be having performance issues, please respond to the questions I posted there.