[FFmpeg-user] Colorchart and colormap

[Paul B Mahol]

On Mon, Apr 25, 2022 at 9:16 PM Michael Koch <astroelectronic at t-online.de>
wrote:

> Hi,
>
> I have some remarks and questions about the new "colorchart" source and
> "colormap" filter.
>
> In "colorchart" is a small error in the yellow field. It should be 231,
> 199, 31.
> Source:
> https://www.xritephoto.com/documents/literature/en/ColorData-1p_EN.pdf
>
> "colorchart" is missing in the table of contents of the documentation.
>
> Could you please also add an option for the chinese version which has
> slightly different colors?
> Source: https://www.aliexpress.com/item/32738129067.html
> The RGB values are shown in the 5th picture. Code is below.
>
> In "colormap" I'd like to know how the color from the "source" image is
> calculated. If a real image of a ColorChecker is used, then the borders
> between the fields must somehow be excluded.
>

Center pixel of patch is picked, that is fastest way.
There is separate software for processing real world colorcharts.
(Dealing with geometric transformation and color averaging)


> Is the average color over the whole 64x64 field used? Or is only one
> pixel used, from the center of the 64x64 field? Or is it the average
> color over a smaller area, for example the central 24x24 pixels?
>
> Michael
>
>
>
> static const uint8_t ref_china_colors[][3] = {
>      { 115,  82,  69 }, // dark skin
>      { 204, 161, 141 }, // light skin
>      { 101, 134, 179 }, // blue sky
>      {  89, 109,  61 }, // foliage
>      { 141, 137, 194 }, // blue flower
>      { 132, 228, 208 }, // bluish green
>
>      { 249, 118,  35 }, // orange
>      {  80,  91, 182 }, // purple red
>      { 222,  91, 125 }, // moderate red
>      {  91,  63, 123 }, // purple
>      { 173, 232,  91 }, // yellow green
>      { 255, 164,  26 }, // orange yellow
>
>      {  44,  56, 142 }, // blue
>      {  74, 148,  81 }, // green
>      { 179,  42,  50 }, // red
>      { 250, 226,  21 }, // yellow
>      { 191,  81, 160 }, // magenta
>      {   6, 142, 172 }, // cyan
>
>      { 252, 252, 252 }, // white
>      { 230, 230, 230 }, // neutral 8
>      { 200, 200, 200 }, // neutral 65
>      { 143, 143, 142 }, // neutral 5
>      { 100, 100, 100 }, // neutral 35
>      {  50,  50,  50 }, // black
> };
>
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