Re: Compositing transparent png over image using Magick++ GraphicsMagick API

Thanks for the quick response.
I'm not trying to create transparent jpeg, I'm trying to compose
transparent png onto an image, so that only non-transparent pixels are
composed.
For example, when I execute this from command line:
gm compose watermark.png source.jpg destination.jpg
I get the desired effect. Only non-transparent pixels from png image are
composed to destination image.
What I'm interested in is how to achive this with magick++ api?
Should I create an empty image with type TrueColorMatteType first and than
compose both source and watermark images on that image instead of composing
directly to source image?

Dragan


On Tue, Jan 28, 2014 at 7:11 PM, <[email protected]> wrote:

> The JPEG format does not support transparency. Try saving as png instead.
>
>
> On Tuesday, 28 January 2014, Dragan Jotanovic <[email protected]> wrote:
>
>>  Hello,
>>
>> I am trying to compose png watermark with transparency using Magick++
>> API, but after saving, image the transparency is lost.
>>
>> The code I use is:
>>
>> Image source("source.jpg");Image watermark("watermark.png");
>> source.composite(watermark, 0, 0, DissolveCompositeOp);
>> source.write("destination.jpg");
>>
>>  I tried explicitly setting image type (of both source and watermark) to
>> TrueColorMatteType, but no change, transparent color is still black
>> instead of transparent.
>>
>> Does anyone know what else needs to be done in order to preserve
>> transparency after composition?
>>
>>
>> Dragan
>>
>
>
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