BUG converting to png with resize - Filesize

[zaratol]

Hi,

all converts are done in Windows:
Version: ImageMagick 6.6.9-4 2011-04-01 Q16

i did convert a rather simple tif file to a png File:
convert input.tif -resize 400x400 png32:output.png

http://home.arcor.de/durius.obsidian/input.tif is 1,8 MB, http://home.arcor.de/durius.obsidian/output.png is 700 kb, which is way to much after this kind of resize.
So i did first a resize to tif:

convert input.tif -resize 400x400 tifout.tif
http://home.arcor.de/durius.obsidian/tifout.tif 104 kb thats more like it. so what will happen when i convert this file to png

convert tifout.tif png32:firsttif.png
http://home.arcor.de/durius.obsidian/firsttif.png 60 kb, yeah

Of course i can do that in one commandline via pipe, but something is wrong here

[fmw42]

try adding -strip to your command

convert input.tif -strip -resize 400x400 input1.png
identify input1.png
input1.png PNG 400x400 400x400+0+0 8-bit DirectClass 50.2KB 0.000u 0:00.010

[zaratol]

I would like to preserve profile Information.

if i do it via tif first the final png ist still only 60kb WITH profile

or do i miss something?

[anthony]

Do it at least once. It will let you see how much of that image size really is a 'constant sized' profile.

[glennrp]

Your output png contains a "tiff profile" that is 1.4MB, compressed to
a little under 700kb and stored in a zTXt chunk. If you don't want to
lose that profile, then that's probably the best we can do. Apparently
the profile got lost in the tif-to-tif conversion.

Run "identify -verbose" on your files to
see what's happening.

When you convert the second tif to png there are some
profiles, but the big "tiff" one is gone.

[zaratol]

The Subimage in tag 37724?

I was wondering about that warning message, espacialy since i did create the most simple image.

Regarding the Information here: http://www.awaresystems.be/imaging/tiff ... edata.html this is some kind Image Source Data only used by Adobe photoshop

id did a quick search in the Forum after this tag, it seems ImageMagick does not know/care about this tag. I would guess it is only a recent addition of how Photoshop cs4/5 writes tif Images.
Normaly unknown Tags are discarded, this happens in the tif to tif conversion (i tried tif to jpg conversion, the tag is also discarded)

Since i do not know what is saved in this tag i would suggest that a png conversion discards unknown tif tags - standard ImageMagick behaviour.
I even tried convert input.tif -resize 400x400 +profile "8BIM" png32:output.png no change in filesize.

Should i open a sperated thread about the tag 37724? If i search after this tag here i find 3 Pages worth of Post, is there no better way to handle this Tag?

[glennrp]

That would be the job of the TIFF decoder to discard the unknown data, not the PNG encoder's.
Yes, there is a small 8bim profile in there as well, but discarding that does not get rid of the
unknown profile.

[zaratol]

@Glennrp: I agree this should be done in the TIFF decoder if teh data is not usable.
In thread: viewtopic.php?f=3&t=18557 magick states:

We could add an option to ignore a tag but it is not currently supported.

(problem with the same Tag) So i guess this not an option right now.

Perhaps i should clarify what i want to preserve:

• XMP
  IPTC
  ICC/ICM Color Profiles

right now i run with this command line:

convert input.tif +profile "!XMP, !IPTC, !ICC, *" -resize 400x400 output.png

this seems to do the trick, still it would be better if such non usable data would be handled directly.