Hi Ben,
Thanks very much for the tips!
I tried op.background("#ffffff") and it doesn't work for our case.
After some research, I only added op.colorspace("sRGB") and it worked.
As you said, "alpha remove" doesn't seem to have done anything.
Best,
Ying
On Mon, Sep 14, 2020 at 4:23 PM Ben Heartland <b...@benheartland.com> wrote:
> Hi Ying,
>
> Because JPG can't handle transparency, the alpha channel will be removed
> anyway by the conversion, so adding a line to remove it explicitly is
> unlikely to change anything. I'm not familiar with ImageMagick, but from a
> general graphics point of view, there are two possible solutions:
>
> (1) convert to PNG instead of JPG (since PNG can handle transparency)
> (2) get ImageMagick to use white as the background fill (or whatever your
> chosen colour is)
>
> It seems that ImageMagickThumbnailFilter.java
> <https://github.com/DSpace/DSpace/blob/main/dspace-api/src/main/java/org/dspace/app/mediafilter/ImageMagickThumbnailFilter.java>
> can
> only produce JPGs, so option (2) would seem to be the way forward. Looking
> at the ImageMagick docs
> <http://im4java.sourceforge.net/api/org/im4java/core/IMOps.html#background(java.lang.String)>,
> my best guess at how to do this would be to do something like:
>
> Replace:
> if (flatten) {
> op.flatten();
> }
> with:
> if (flatten) {
> // First set the background colour: could also try using e.g.
> "white" or "rgb(255,255,255)"
> op.background("#ffffff")
> // Then flatten the image
> op.flatten();
> }
>
> Hopefully others more familiar with ImageMagick can correct any mistakes
> in my reasoning and/or syntax!
>
> Ben
>
> On Saturday, 12 September 2020 at 01:31:40 UTC+1 elsa...@gmail.com wrote:
>
>> Hi,
>>
>> We have some pdfs with transparent background. When using ImageMagick to
>> convert to jpg thumbnails, it has black background. I set
>> org.dspace.app.mediafilter.ImageMagickThumbnailFilter.flatten = true
>> in dspace.cfg, even add this line to ImageMagickThumbnailFilter.java in
>> getImageFile method.
>>
>> op.alpha("remove");
>>
>> Doesn't seem to work.
>>
>> We are on DSpace 6.3 and using ImageMagick 6.9.10-68, and GPL Ghostscript
>> 9.25 (2018-09-13) on redhat linux.
>>
>> Is there anyone knows how to solve this problem?
>>
>> Thanks,
>> Ying
>>
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