[Gambas-user] About Image.Pixel

[Bruce Steers]

On Tue, 15 Aug 2023 at 12:13, Bruce Steers <bsteers4 at gmail.com> wrote:

>
>
> On Mon, 14 Aug 2023 at 23:37, Bruce Steers <bsteers4 at gmail.com> wrote:
>
>>
>>
>> On Mon, 14 Aug 2023, 21:19 Fabien Bodard, <gambas.fr at gmail.com> wrote:
>>
>>> Hi,
>>>
>>> Dim hImg As New Image(1, 1, Color.red)
>>> dim a as Integer[]
>>>
>>> a = hImg.Pixels
>>>   Print a[0]
>>>   Print hImg[0, 0]
>>>
>>> result :
>>> -65536
>>> 16711680
>>>
>>>
>>> Why ?
>>>
>>> --
>>> Fabien Bodard
>>>
>>
>> According to wiki Image[x,y] returns a "colour"
>> Image.pixels[n] will be from an array of "32 bits integers"
>>
>> I don't understand it but seems could be a difference?
>>
>>
>> Respects
>> BruceS
>>
>
>
> I think i figured it out..
> I noticed the warning on the wiki Color page..
> http://gambaswiki.org/wiki/comp/gb.qt4/color
>
> In Gambas, the alpha color component is inverted in comparison to standard
> color coding. In other words, an alpha component of zero is fully opaque,
> and an alpha component of 255 is fully transparent
>
>
> So I used this code that converts to hex values...
>
> Public Sub Form_Open()
>
>   Dim hImg As New Image(1, 1, Color.red)
>
>   Dim aInt As Integer[]
>
>   Print "red = "; Color.Red
>   aInt = hImg.Pixels
>
>   Print aInt[0]
>   Print hImg[0, 0]
>
> Dim A, R, G, B As String
>
> A = Hex(Lsr(aInt[0], 24) And &HFF, 2)
> R = Hex(Lsr(aInt[0], 16) And &HFF, 2)
> G = Hex(Lsr(aInt[0], 8) And &HFF, 2)
> B = Hex(aInt[0] And &HFF, 2)
> Print A, R, G, B
>
> A = Hex(255 - Lsr(hImg[0, 0], 24) And &HFF, 2)  ' Note this line uses 255-
> as wiki says Alpha values in gambas are reversed
> R = Hex(Lsr(hImg[0, 0], 16) And &HFF, 2)
> G = Hex(Lsr(hImg[0, 0], 8) And &HFF, 2)
> B = Hex(hImg[0, 0] And &HFF, 2)
>
> Print A, R, G, B
>
> End
>
>
> results..
> red = 16711680
> -65536
> 16711680
> FF      FF      00      00
> FF      FF      00      00
>
> Note for the Image[n,n] array i use 255- on the alpha value to reverse it.
> It seems the Pixels[] array does not reverse the alpha value but the
> Image[] array does
>
> I have no idea how to convert the 1st 32bit alpha part as a color integers
> all i have is that Hex conversion but i think i found the problem.
>

Aah so after Benoits advise i guess we should create image like this...

  Dim hImg As New Image(1, 1, Color.red)
  hImg.Format = "BGRA"

But that is only a guess ;)
Thankfully Benoit is here :)

Happy holiday Ben, er Ascention day is it?
My IDE started singing this morning lol :)

Respects
BruceS
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