Legacy ImageMagick Discussions Archive

Hi,

I'm new in ImageMagic. Im trying to resize png file with this simple command

convert wlbn_120809_085727_609.png -resize 1000x resize_image.png

but result differs against original in colour and size too. Colour of the result image is more darker than original (i've tried also -quality, -colorspace functions)
Same problem i see in converting FIT, FITS to PNG or only displaying FIT, FITS. Displayed/converted FITS has more black and constrast places than original.

Im working with 8bit grayscale astrophotos of Sun surface and with imagemagick i want to optimize further photos processing.

Thank you for your advices. J.

what version of IM and platform are you using? grayscale images are now handled as linear rather than sRGB. but there was a transition so some versions of IM may have bugs.

does it happen without the resize?

can you post a link to one of your grayscale images?

otherwise perhaps try

convert grayscale.png -colorspace sRGB -resize ... result

r u really upsizing by 1000 times?

henrywho wrote:r u really upsizing by 1000 times?

No that is not 1000 times, it is 1000 pixels wide!!!!

For a 1000 times resize you would use 100000%

Or using IMv7 'magick' command you can use -resize '%[fx:w*1000]x' to DIY the calculation yourself!

That was my last update to IMv7 CLI. I have been snowed by 'life' since, but trying to get this into 'setting' arguments (like -size) as well as for 'operator' arguments such as the -resize.

OK what am i doing....?

Versions of software:

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$ uname -or
3.0.36-1-lts GNU/Linux
$ convert -version
Version: ImageMagick 6.7.8-1 2012-07-06 Q16 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2012 ImageMagick Studio LLC
Features:

Resizing sample PNG:

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$ identify original.png 
original.png PNG 744x1052 744x1052+0+0 8-bit DirectClass 33.5KB 0.000u 0:00.000
$ convert original.png -resize 50% original_resized.png
$ identify original_resized.png
original_resized.png PNG 372x526 372x526+0+0 8-bit PseudoClass 256c 7.39KB 0.000u 0:00.010

In resized image i see changes in gray colour. It is darker.

And same process of image with -resize 100% with same result:

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$ identify original.png 
original.png PNG 744x1052 744x1052+0+0 8-bit DirectClass 33.5KB 0.000u 0:00.000
$ convert original.png -resize 100% original_notresized.png
$ identify original_notresized.png
original_notresized.png PNG 744x1052 744x1052+0+0 8-bit PseudoClass 256c 15.3KB 0.000u 0:00.000

i think its not problem of -resize. Try:

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convert original.png original2.png

gets same result. -colospace RGB doesn't help.

You can download these sample images here:

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http://www.ulozto.net/xnDnuoh/pngimages-tar-gz

Documentation of convert -resize command is huge. I hope that you help me. I have another but similar issue about converting and displaying FITS, FIT images.

Thanks a lot. J.

With 6.7.8-9 Win64 DLL, gray images appear to be causing troubles again:

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convert rings_lg_orig.png -alpha off -colorspace RGB -filter RobidouxSharp -distort resize 50% -colorspace sRGB -alpha off +repage -quality 95% test1.png

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convert rings_lg_orig.png -alpha off -evaluate POW 2.2 -filter RobidouxSharp -distort resize 50% -gamma 2.2 -alpha off +repage -quality 95% test2.png

test1.png is noticeably lighter than it should be. Juray's original.png is not revealing this problem though.

http://www.imagemagick.org/Usage/resize ... g_orig.png

It works again by adding "-set colorspace sRGB".

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convert rings_lg_orig.png -alpha off -set colorspace sRGB -colorspace RGB -filter RobidouxSharp -distort resize 50% -colorspace sRGB -alpha off +repage -quality 95% test1b.png

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