PNG and saving transpareny

[klumy]

hello,

in IrfanView it is possible to set which colour should be transpareny if you save a PNG image, by clicking on the colour of the image.

Such a feature would be really useful for XNView.
I often use this feature because I use the image for Powerpoint. So the unuseful background of the image is transparent and can easily be integrated into powerpoint

[xnview]

in IrfanView it is possible to set which colour should be transpareny if you save a PNG image, by clicking on the colour of the image.

Such a feature would be really useful for XNView.
I often use this feature because I use the image for Powerpoint. So the unuseful background of the image is transparent and can easily be integrated into powerpoint

You can do that by editing colormap ("Image > Edit color map").

[klumy]

this feature is invisible here

[helmut]

this feature is invisible here

If your image is not a palette image (<=256 colours), you won't be able to edit the colour palette and set transparency in XnView.

I even think that it's not possible at all to set transparency for PNGs with more than 256 colours.

[klumy]

I don't think its dependable from the number of colours

I have some PNG with more than 256 colors created with IRfanView and they also support transparency

[xnview]

I don't think its dependable from the number of colours

I have some PNG with more than 256 colors created with IRfanView and they also support transparency

So you want to set the transparency for one color, and for a picture more than 256 colors?

[Drahken]

That is an official feature of PNGs. You can use alpha transparency on either a 256, a greyscale, or a truecolor PNG (although most progs only allow creating truecolor and greyscale PNGs with alpha transparency), and you can use single color transparency on a 256 color, a greyscale, or a truecolor PNG. In fact, one workaround for M$IE's crappy PNG support is to set a transparent color in the image AND set an alpha transparency. Decent browsers will show the image with the alpha transparency, and M$IE will fallback to single color transparency.
The problem is, I don't know how xnview would allow you to choose a single transparent color for PNGs with >256 colors, since such images don't have a "palette" (as such, all images have a palette).

As far as choosing the transparent color for 256 or less images, it works fine for me, I've used it several times.

[xnview]

That is an official feature of PNGs. You can use alpha transparency on either a 256, a greyscale, or a truecolor PNG (although most progs only allow creating truecolor and greyscale PNGs with alpha transparency), and you can use single color transparency on a 256 color, a greyscale, or a truecolor PNG. In fact, one workaround for M$IE's crappy PNG support is to set a transparent color in the image AND set an alpha transparency. Decent browsers will show the image with the alpha transparency, and M$IE will fallback to single color transparency.
The problem is, I don't know how xnview would allow you to choose a single transparent color for PNGs with >256 colors, since such images don't have a "palette" (as such, all images have a palette).

As far as choosing the transparent color for 256 or less images, it works fine for me, I've used it several times.

Currently single color for transparency on a 24bits picture is not possible

[Drahken]

Here's a quick demo I made if anyone wants to play around with it:
http://allspark.net/cypherswipe/trans-truecolor-png.png
Note: Not all browsers or viewers can handle this kind of transparency. Gecko based browsers such as netscape and firefox handle it fine, I'm pretty sure opera does too. FYI the big area in the middle is the transparent part.

[GeorgD]

Currently single color for transparency on a 24bits picture is not possible

Is this still (1.90beta2) the current state? I understood your post (Fri Oct 29, 2004 in http://newsgroup.xnview.com/viewtopic.php?t=561) differently *confused*

/Georg

[dma_k]

You can do that by editing colormap ("Image > Edit color map").

Thanks for the hint. First I wrongly tried to play with Options > Genral Write > PNG > Set the transparency value, then I learned how to use a Image > Edit color map, I finally understood that I need to use not more than 265 colors in order File > Export > PNG > Set transparency color button to get enabled

[Jaff]

Currently single color for transparency on a 24bits picture is not possible

That's not a problem. XN can generate a warning window to increase number of colors to RGBA (32bit) and continue to generate mask from the chosen color.

[MaxSt]

That's not a problem.

Incomplete support for PNG format *is* a problem for XnView.