[PD-dev] pd file format: color settings

[Roman Haefeli]

I assume, this is because a 24bit integer cannot be saved with full
precision with Pd, since Pd seems to strip off some bits when saving a
floating point value (or when printing or displaying it). If the color
would be encoded as RGB 8bpp, it would look different after saving and
restoring it. So a smaller range had to be used. 

When sending 'color' messages to the iemguis directly, the full 24bit
resolution can be used.

Roman



On Sat, 2010-02-13 at 18:32 -0500, Martin Peach wrote:
> Ah yes, in g_all_guis.c line 281:
> 
> void iemgui_all_colfromload(t_iemgui *iemgui, int *bflcol)
> {
>      if(bflcol[0] < 0)
>      {
>          bflcol[0] = -1 - bflcol[0];
>          iemgui->x_bcol = ((bflcol[0] & 0x3f000) << 6)|((bflcol[0] & 
> 0xfc0) << 4)|
>              ((bflcol[0] & 0x3f) << 2);
>      }
>      else
>      {
>          bflcol[0] = iemgui_modulo_color(bflcol[0]);
>          iemgui->x_bcol = iemgui_color_hex[bflcol[0]];
>      }
> 
> ...so if the colour is negative it's a negated (all bits flipped) 18-bit 
> rgb value and if it's positive it's an indexed colour from the iemgui 
> palette.
> 111111RRRRRRGGGGGGBBBBBB
> is bit-flipped to get:
> 000000rrrrrrggggggbbbbbb
> which is shifted into this:
> rrrrrr00gggggg00bbbbbb00
> so the 2 LSBs of each colour are set to 0. I don't know why.
> 
> Martin
> 
> Robert Schwarz wrote:
> > Thanks for the quick answer.
> > 
> > The concept of embedding three 8 bit components in one integer was clear
> > to me, but I think that pd doesn't really use all 8 bits for the colors.
> > Or maybe there is some issue with 2-complements or something.
> > 
> > For example, if I want to create three bang objects, in red (#ff0000),
> > green (#00ff00) and blue (#0000ff), your formula gives values of:
> > 16711680, 65280, 255 for the three colors.
> > 
> > But I insert them in a patch, like:
> > 
> > #N canvas 825 10 450 300 10;
> > #X obj 0 0 bng 15 200 50 0 target empty empty 0 0 0 8 16711680 0 0 ;
> > #X obj 0 15 bng 15 200 50 0 target empty empty 0 0 0 8 65280 0 0 ;
> > #X obj 0 30 bng 15 200 50 0 target empty empty 0 0 0 8 255 0 0 ;
> > 
> > I see the colors white, white, yellow.
> > 
> > Now, when I change the colors by hand, to really get red, blue and green
> > on the bang objects and save the file, it reads:
> > 
> > #N canvas 825 10 450 300 10;
> > #X obj 0 0 bng 15 200 50 0 target empty empty 0 0 0 8 -258049 -1 -1 ;
> > #X obj 0 15 bng 15 200 50 0 target empty empty 0 0 0 8 -4033 -1 -1 ;
> > #X obj 0 30 bng 15 200 50 0 target empty empty 0 0 0 8 -64 -1 -1 ;
> > 
> > So it uses negative numbers, and -64 means "full blue".
> > Now, when I re-open the same file and look at the properties of the blue
> > bang object, the color now reads: #0000fc instead of the #0000ff I
> > entered just before saving.
> > 
> > That's why I suspect some lower resolution going on. I tried to browse
> > this part in the sources, but all the GUI code confuses me.
> > 
> > For your interest, this patch results for colors of #040000, #000400 and
> > #000004 set by hand in the properties window:
> > 
> > #X obj 0 0 bng 15 200 50 0 target empty empty 0 0 0 8 -4097 -1 -1;
> > #X obj 0 15 bng 15 200 50 0 target empty empty 0 0 0 8 -65 -1 -1;
> > #X obj 0 30 bng 15 200 50 0 target empty empty 0 0 0 8 -2 -1 -1;
> > 
> > Setting colors to lower values, like #010000 results in getting them
> > rounded down to #000000.
> > 
> > So, the resolution is apparently 256/4 = 64 values, or 6 bits.
> > 
> > Indeed, if I replace the formula with:
> > 
> > color = (-([red]+1)/4*64*64) - (([green]+1)/4*64) - ([blue]+1)/4
> > 
> > I get the same values that Pure Data produces.
> > Hm, I might just have solved my problem.
> > 
> > It's still weird and some developer could check this our or change the
> > documentation.
> > 
> > Cheers, Robert
> > 
> > On 02/13/2010 11:08 PM, Martin Peach wrote:
> >> That formula should read:
> >>  color = ([red] * 65536) + ([green] * 256) + ([blue])
> >> In binary the idea is to shift the 8 'red' bits 16 to the left, then add
> >> 8 'green' bits shifted 8 bits, and finally 8 'blue' bits, so in all 24
> >> bits are occupied.
> >> Multiplying the blue value by -1 in the original formula has the effect
> >> of setting the 16 bits to the left of it to 1, so you get different
> >> shades of pure blue.
> >>
> >> Martin
> >>
> >> Robert Schwarz wrote:
> >>> Hi all,
> >>>
> >>> I recently tried writing patches in a text editor (or from scripts) and
> >>> had problems getting the color settings right, for bang elements.
> >>>
> >>> There is some documentation at
> >>> http://puredata.info/docs/developer/fileformat
> >>> with the explanation:
> >>>
> >>>> Color: Some graphical elements have color attributes. Per color only
> >>>> one signed integer value is stored that contains the three 8-bit
> >>>> color components (RGB). Formula to calculate color attribute values:
> >>>>
> >>>> color = ( [red] * -65536) + ( [green] * -256) + ( [blue] * -1)
> >>>>
> >>>> Where [red], [green], [blue] obviously represent the three color
> >>>> components, their values range from 0 to 255. They apply to the
> >>>> attributes [background color], [front color], [label color] of
> >>>> various elements.
> >>> I tried that, but it didn't work. Instead of showing the whole spectrum
> >>> I just got different shades of blue. Also, when I opened one of my
> >>> handwritten patches in PureData, looked at the color settings and saved,
> >>> the resulting numbers changed. I assume that some kind of rounding is
> >>> happening, and colors are actually saved in lower resolution.
> >>>
> >>> Do you have any ideas?
> >>>
> >>> Also, my application is a 13x13 button matrix, each triggering different
> >>> chords via MIDI. The buttons should be color coded. Obviously, it's too
> >>> much work setting all colors individually and I might want to create
> >>> several of these patches with different colors.
> >>> Maybe there is another obvious solution I didn't see.
> >>>
> >>> Any help is appreciated!
> >>>
> >>> (I'm using standard pd 0.42_5 on Arch Linux, but this shouldn't make a
> >>> difference.)
> >>>
> > 
> 
> 
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