why it will change the color

[trymoremore]

the color of background changed from white to black. how to prevent it?

[romainmenke]

is the white background actually transparant? Guetzli doesn't support images with transparency.

[trymoremore]

@romainmenke thank you very much. and whether there is no way to compression images with transparency in guetzli?

[robryk]

There is no transparency support in JPEGs as they are supported by most viewers.

[Algae666]

Is it at least possible to create a setting which allows changing the transparency flattening color (say, from the default black to white instead)?

[Algae666]

When I changed the BlendOnBlack function in guetzli.cc to this:

inline uint8_t BlendOnWhite(const uint8_t val, const uint8_t alpha) { if (alpha < 1) return 255 - ((static_cast(val) * static_cast(alpha) + 128) / 255); return val; }

I got my source image on white background (this is for an image with transparency either fully on or fully off... if there were some blending at the edges, this would probably not suffice).

[LongBu]

Hi there,

Is there any intention to allow alpha channel support/preservation (eg correlation from the original image to the prospective target image) for *.pngs in the future?

Thanks!

[istvan-ujjmeszaros]

Please modify Guetzli to use white color for flattening instead of black. Black has no use in any circumstances.