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<p>Hi Tobias,</p>
<p><br>
</p>
<p>oops, I mistook the depth with the number of bits per channel. Sorry and many thanks for your explanations!</p>
<p><br>
</p>
<p>How would one fix the upscaling issue? <span style="font-size: 12pt;">Form>>#</span><span style="font-size: 12pt;">colormapIfNeededFor: returns nil in example 3, the comment in Color>>#colorMapIfNeededFrom:to: states this task is delegated to BitBlt. Is
this comment wrong or is the defect in the primitive called that is in BitBlt>>#copyBits?</span></p>
<p><span style="font-size: 12pt;"><br>
</span></p>
<p><span style="font-size: 12pt;">Best,</span></p>
<p><span style="font-size: 12pt;">Christoph</span></p>
<br>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>Von:</b> Squeak-dev <squeak-dev-bounces@lists.squeakfoundation.org> im Auftrag von Tobias Pape <Das.Linux@gmx.de><br>
<b>Gesendet:</b> Montag, 9. September 2019 14:56 Uhr<br>
<b>An:</b> The general-purpose Squeak developers list<br>
<b>Betreff:</b> Re: [squeak-dev] Bug in Form>>#asFormOfDepth:?</font>
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<div class="PlainText">Hi Christoph,<br>
<br>
> On 09.09.2019, at 13:25, Thiede, Christoph <Christoph.Thiede@student.hpi.uni-potsdam.de> wrote:<br>
> <br>
> Hi all,<br>
> <br>
> consider the following example (print it):<br>
> <br>
> "Example 1"<br>
> f := Form extent: 1 asPoint depth: 1.<br>
> f colorAt: 0 @ 0 put: Color red.<br>
> g := f asFormOfDepth: 2.<br>
> g colorAt: 0 @ 0<br>
> <br>
> Expected output: Color red.<br>
> Actual output: Color black!<br>
<br>
No, Forms of depth 1 are black and white, and of depth2 are gray.<br>
<br>
> <br>
> Other examples:<br>
> <br>
> "Example 2"<br>
> f := Form extent: 1 asPoint depth: 1.<br>
> f colorAt: 0 @ 0 put: Color red.<br>
> g := f asFormOfDepth: 32.<br>
> g colorAt: 0 @ 0 "--> (Color r: 0.0 g: 0.0 b: 0.004)"<br>
<br>
yes, because you go from black/white to 32bit. I would have expected r0g0b0, but there might some rounding go on.<br>
<br>
> <br>
> "Example 3"<br>
> f := Form extent: 1 asPoint depth: 16.<br>
> f colorAt: 0 @ 0 put: Color red.<br>
> g := f asFormOfDepth: 32.<br>
> g colorAt: 0 @ 0 "--> (Color r: 0.973 g: 0.0 b: 0.0)"<br>
<br>
<br>
<br>
Something's wonky here!<br>
If we do <br>
<br>
(((Form extent: 1 asPoint depth: 16)<br>
colorAt: 0 @ 0 put: Color red)<br>
asFormOfDepth: 32)<br>
pixelValueAt: 0@0<br>
<br>
we get <br>
4294443008 (aka 0xFFF80000) which is a 32bit value.<br>
But the meaning is <br>
<br>
11111111 11111000 00000000 00000000<br>
^ alpha ^ r ^ g ^ b<br>
<br>
which means that the r component is not "upscaled" during the #asFormOfDepth: process o.O (see PS)<br>
<br>
<br>
<br>
<br>
> <br>
> I am not familiar with color depths, but afaik Color red could be stored exactly using only 1 bit? Do I misunderstand the concept or is this really a bad output?<br>
<br>
No, the first bit depth to support red is 4 bit.<br>
<br>
Have a look at Color class>>colorFromPixelValue: p depth: d<br>
<br>
BTW: You can use a ColorForm to work with your own palette, so that you can have for example a 1-bit form with 1=yellow & 0=red…<br>
<br>
<br>
Best regards<br>
-Tobias<br>
<br>
> <br>
> (I came across to this when performing #collectColors: on an 8 bit ColorForm loaded from disk, which did not work as expected.)<br>
> <br>
> Best,<br>
> Christoph<br>
<br>
PS: PS:<br>
Color red is r:1.0 g:0.0 b:0.0 but stored in a different fashion:<br>
<br>
Color comment:<br>
"<br>
Think of Color's instance variables as:<br>
r amount of red, a Float between 0.0 and 1.0.<br>
g amount of green, a Float between 0.0 and 1.0.<br>
b amount of blue, a Float between 0.0 and 1.0.<br>
(But, in fact, the three are encoded as values from 0 to 1023 and combined in a single integer, rgb. The user does not need to know this.)<br>
"<br>
that means "Color red" is stored as 0x3FF00000 or, <br>
<br>
1111111111 0000000000 0000000000<br>
^ red ^ green ^ blue<br>
<br>
that makes 10 bit per component.<br>
<br>
However, in the 16 bit form we have only 5 bit per component, so, <br>
<br>
f := Form extent: 1 asPoint depth: 16.<br>
f colorAt: 0 @ 0 put: Color red.<br>
f pixelValueAt: 0@0.<br>
<br>
yields 0x7C00 aka<br>
<br>
11111 00000 00000<br>
^ r ^ g ^ b<br>
<br>
<br>
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