Re: Removing all "not essential" data from an image file.

Thanks for your quick reply Martin :o)

2010/4/27 Martin Weis <[email protected]>

> Hallo Eric!
>
> Eric Arrigo schrieb:
> > I was using pngcrush for years in order to reduce my websites images,
> > thinking that this would actually remove any unused bit of data.
> > Yesterday, I used the data uri kitchen on one of those pngcrushed images,
> > and I was puzzled to discover that the header still hold some text
> > information about the application that created the image.
> >
> > Is there a way to strip the image meta data with image-magick?
>
> converting to plain ppm and back usually does this kind of trick, if you
> you do not find an option for it.
>
> > Here is the data uri of the image:
> >
> data:image/png,%89PNG%0D%0A%1A%0A%00%00%00%0DIHDR%00%00%00%0C%00%00%00%0C%08%06%00%00%00Vu%5C%E7%00%00%00%19tEXtSoftware%00Adobe%20ImageReadyq%C9e%3C%00%00%01eIDAT(SURM%2BDa%14~%7F%0A%0B%0B%D24%92F%92%92D%92%B2%10%7F%40IR%16vR%B2%91dG%8C13%BE%BF%F2%B1%92%91%94%8F%C2J%B1%B1%B0%96%14w1S%F7%BC%EFe%8Es%9E%3B%D7%C7%5Bo%EF%E9%DC%E79%E79%CF%B9%C6%9F%2B%8BS*%E6%D1j%03%D3z%13%D3F3%D3f%0B%D3v%1B%DB%9Dv%B9%1Dxi%A5%DES%AC%018%15cw%DC%1F%02%FF%12%B7Z%7FI%BB%9DL%D9%84g(%5D%CBz%A3S%CC%BF%F0%E7C%86%ED~%F7%7Fp%A9%A3A%B5l%82%5Dn%08%C0%E2%C7sH%2C%BC%22%17%81%A3%8E%06%81%C8P%B0%3B%1BA2%B8%9A%60v%05%5C%97%1B%0C%C1k%8Dx%0DtK%97%1FIR9%B8%9Edw%3A%0C%82J%C4%D0%A2Bq%26j%A7%9A%83%BBY%10%F4h%17w9%1E%C6%92%A7t%8D%3A%C5%06l%91%E1%CEG%F1%C1%1E%F6%82%A4%95U%86%BE%C5%F7'%A6%A5j%A6L%9D%12B%9F%A1Y%AB%DD%CEpp3%85%D8%9D%0Cpp%9FD%EC%2FV%C2Mc%F7%BA%60%DD%D7%DB%23%B3%CD%B3%3D%EAc%7B%D0S%22O%B3%BB%18C%AC8%3FY%253%C8%06%FFY%A7n%E8%80%AAYdhe%7F%A1%82%FD%F9r%25x%06%BF%86l%10n%C9%2C%20%E9nd%40%D5%8C%C5.%C7%01V%EC7%84i
> %!
> >  BC%B3%D8%CC%F1W%00%00%00%00IEND%AEB%60%82
> >
> > You may see some information about Adobe ImageReady that take almost 10%
> of
> > the image size and that I would like to remove (i tried "-max 0" in
> pngcrush
> > to limit the IDAT size, but it seems this information is not into the
> IDAT
> > chunk).
>
> minimum is 1:
>       -max maximum_IDAT_size
>                 Set the maximum idat size to be used when creating the
> compression buffer.[1 through 524288]
>
>
I tried "1" but it seems I was wrong when thinking that IDAT was the "Extra
data"... It is the size of some "used for compression" data, and if I use
the value "1", the file size augment by more than 800% :o)


> ...and there are some more text related options, did you try these?
>

After upgrading my old pngcrush to version 1.7.9, I found a new option -rem.
This is not very clear which chunk I am supposed to remove, but "-rem text"
seems to do what I wanted.

I appologize for this off topic subject, but if someone knows a way to
obtain the same result with image-magick, I am still very interested.

(Funily, converting the png to PPM and bac to PNG and cruching it with "-rem
text" gives a slightly bigger file that crushing the original png with "-rem
text" (18 extra bytes)).

Eric



>
> > While I am in questions, would it be any way to have Image-Magick do
> > pngcrush's job (especially the -reduce -brute options) so I don't need to
> > use two sets of tools?
>
> sorry, I do not know.
>
> Martin
>
>


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