Resizing cielab image - don't understand background color

[olafkarsten]

Hello, after messing around ...
in short: I need some help.
Goal: Resize input image, after that put it centered on a white canvas. Outputimage have to be in cielab colorspace and tif format, 8bit. Code of choice:

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convert -verbose rose: -colorspace lab -filter quadratic -resize 500x500\! -gravity center -crop 2200x1800+0+0\! -layers flatten -depth 8 -compress LZW rose.tif

Don't work. Background is something in the redish area. Whereas:

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convert -verbose rose: -filter quadratic -resize 500x500\! -gravity center -crop 2200x1800+0+0\! -layers flatten -colorspace lab -depth 8 -compress LZW rose.tif

works (note: colorspace conversion at the end). BUT we have found in our tests, that colorspace conversion to cielab before the resize operation gives us better results.

If you don't have an tif-viewer, use rose.JPG instead. Works, too.

Any help is really appreciated.

Thanx.

[fmw42]

IM does not process background colors, except in sRGB, as far as I know. Even if you specify HSL or other acceptable colors, they get converted to sRGB values.

Does this do what you want?

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convert -verbose rose: -colorspace lab -filter quadratic -resize 500x500\! \
-set colorspace LAB -colorspace sRGB \
-gravity center -background white -extent 2200x1800 -colorspace lab\
-depth 8 -compress LZW rose.tif

[olafkarsten]

Ah, I see. That information in the morning would have saved me a few grey hairs.

Thanks for the fast help. I think that works for a starting point. In our case (a script) it is possible, that the input image is bigger in size than the target canvas - therefore the variant with the crop. But i will play around a bit with your variant and hopefully find a way. In any case - as usual - i have learned something from your post. Thanks very much!!!

[fmw42]

Not really sure what you are trying to do. So hard to say. It looks like you just want to enlarge rose to 500x500 and then put in inside a (white) background of 2200x1800. -extent will do that for you. See slight reordering of my command above.

[olafkarsten]

It perfect fits the bill. I didn't now, that extend actually 'crops'. Works perfect in all test cases. Thanx again.

[olafkarsten]

For reference I link to another thread, where we did solve a similiar problem with colorspace and background setting:

viewtopic.php?f=1&t=25781

- Note: the cielab notation with percent sign (%).