image alpha

[murko81]

thank you allot!!
this is working really good!
another question:


if i create a png (4ex in fireworks) with an alpha (4ex 60) and then i close and re-open the image.. the program is able to recognize the fact that the image has an alpha value = 60;
is it possible to do the same thing with qt ? 'cause now when i re-open the image with the viewer i made it reads the initial alpha value as 255

[jpn]

if i create a png (4ex in fireworks) with an alpha (4ex 60) and then i close and re-open the image.. the program is able to recognize the fact that the image has an alpha value = 60;
is it possible to do the same thing with qt ? 'cause now when i re-open the image with the viewer i made it reads the initial alpha value as 255

The image you are showing is created dynamically at run time. You would have to save it back to a file to keep the changes, see QImage::save().

[wysota]

if i create a png (4ex in fireworks) with an alpha (4ex 60) and then i close and re-open the image.. the program is able to recognize the fact that the image has an alpha value = 60;
is it possible to do the same thing with qt ? 'cause now when i re-open the image with the viewer i made it reads the initial alpha value as 255

Qt handles alpha just fine. If you feed it with an image which already has an alpha channel, it will display it correctly without the 'hack' we did here.

[murko81]

of course i save the file before re-opening and of course qt handles fine the alpha channel, maybe i didn't wrote it good (i apologize4my english ).
The fact is:
1- I create an image with a commercial editor and i give to that image an alpha value, and i save it: myfolder/myimage.png , and then i close everything.
2- if i reopen that image with the same commercial editor, it is able to recognize the right alpha value (not only displaying the image in the proper way but also writing it correctly in between the properties of the image)
3-instead if i reopen the image with my self made editor, i am able to display the image correctly but into the properties the alpha value is recognized as the maximum (255)

so the question was: how can i read the rigth alpha value? 'cause if a commercial editor is able to do that maybe i can also:-)

thank you in advance!

[wysota]

3-instead if i reopen the image with my self made editor, i am able to display the image correctly but into the properties the alpha value is recognized as the maximum (255)

so the question was: how can i read the rigth alpha value?

And how do you read the alpha value now? This question is really tricky, as alpha is not a single value but a bitmap.

[murko81]

:-) yes it's not a single value but starting from the fact that in fireworks it shows me it like an unique value i thought that fireworks changes all the alpha values to the same value.. so reading one of them from one single pixel it was enough.. maybe it's not the right way to get it but this is how i did it and this is how i get back always a value = 255;

[wysota]

Attached code shows how to do it properly and attached image shows an example result. Image on the left is the actual image whether image on the right is a bitmap of the alpha channel.