gcrimp@vcn.bc.ca writes:

I want to include full page images of a magazine article in a new document. A single scanned page comes in at about 3.5 MB as a png (saved directly to png from the scan). Any suggestions as to how I might reduce that?

Try Image->Mode->Indexed, and play with the number of colors to get it as small as you can manage while still looking good. Then save it, still using png format.

Full-color pngs are large, but indexed png can be quite small.

Cleaning up the noise from the scan, as you've been doing, can help it look good with a much smaller number of colors. Though it's worth trying the conversion to indexed before cleaning up the page; if the colors are similar, the indexed conversion might do a lot of that work for you. (It seldom seems to in my experience, but it always seems like it *should* ...)

...Akkana

Hi,

A single scanned page comes in at about 3.5 MB as a png (saved directly to png from the scan). Any suggestions as to how I might reduce that?

As already has been suggested: indexed instead of RGB. Another suggestion: reduce the image size - the smaller it is, the less space it needs (obviously).

I guess you already set the compression rate to 9 in the png save dialog?!

One idea I had was to lift the text off of the page and clean up the background. There is a lot of noise, mostly from information showing faintly through from the other side of the thin glossy paper. I spent a lot of time with the select by colour tool to lift the text off the page.

If it is only black and white text, try out the "Threshold" tool (in Image -> Color Tools). It also works on selections.

I
should add that I rescanned as an *.xcf format image to do this work.

Hm - I don't think this makes a difference, both xcf and png are lossless formats, so the pixels should be identical.

When
I saved to *.png, it was pretty much the same size as before (even a little bigger).

Hm. Strange.
Did you have any settings on the scanner different?

Wonderful! I knew about indexing in relation to GIFs. Didn't know PNG could to indexing. Is there anything more intelligent than trial and error for determining how few colours will do while preserving the quality of the page (there is a graphic on the page I am scanning that I would like to look decent).

You can do the indexing manually with the Posterize tool. I don't know if it matches any of the indexing options presented by the mode conversion, but it will reduce colors.

BTW, you should never use any dithering option when indexing an image intended to be saved as PNG - the compression gets better than there are large areas of one color.

HTH, Michael

Michael Schumacher (schumaml@gmx.de) wrote:

You can do the indexing manually with the Posterize tool. I don't know if it matches any of the indexing options presented by the mode conversion, but it will reduce colors.

No, it doesn't match any of the indexing options, it just reduces the numbers of shades per channel (Ok, postering with 6 levels is the same as indexing to the web palette without dithering, but thats it).

Bye, Simon

No, it doesn't match any of the indexing options, it just reduces the numbers of shades per channel (Ok, postering with 6 levels is the same as indexing to the web palette without dithering, but thats it).

Documentation can be really confusing sometimes :) http://docs.gimp.org/de/ch04s05s08.html

The english version has it correct, but doesn't give any further explanation.
http://docs.gimp.org/en/ch04s05s08.html

It should mention that this tool constructs a color cube, the 6x6x6 web palette example might be useful for this.

Michael