8000 Return sRGB from get_pixel_color instead of raw linear values by floraschouw · Pull Request #55 · gimp-mcp/gimp-mcp · GitHub
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Return sRGB from get_pixel_color instead of raw linear values #55

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Return sRGB from get_pixel_color instead of raw linear values #55

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40 changes: 38 additions & 2 deletions gimp-mcp-plugin.py
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,43 @@ def exec_and_get_results(command, context):
return output


# Gegl stores colour in linear light, so Gegl.Color.get_rgba() returns linear
# floats; scaling those by 255 yields linear values wearing an sRGB label, and
# #ff5733 reads back as (255, 24, 8).
#
# babl would convert this for us, but Babl.format() cannot be reached safely
# from here: if babl is not yet initialised it calls babl_fatal() -- "you must
# call babl_init first" -- which aborts the process at the C level and cannot
# be caught from Python. GIMP imports this file during its plug-in scan,
# before that initialisation, so touching babl here makes the whole plug-in
# vanish from the menu. The sRGB transfer function is exact for 8-bit output
# anyway: it round-trips all 256 levels and matches babl on every colour
# tested.


def _linear_to_srgb_u8(value):
"""One linear-light channel (0..1 float) -> 0-255 sRGB byte."""
if value <= 0.0:
return 0
if value <= 0.0031308:
encoded = value * 12.92
else:
encoded = 1.055 * (value ** (1.0 / 2.4)) - 0.055
return max(0, min(255, round(encoded * 255)))


def srgb_bytes_from_color(color):
"""Gegl.Color -> (r, g, b, a) as 0-255 sRGB values."""
red, green, blue, alpha = color.get_rgba()
return (
_linear_to_srgb_u8(red),
_linear_to_srgb_u8(green),
_linear_to_srgb_u8(blue),
# Alpha is stored linearly; it takes no transfer function.
max(0, min(255, round(alpha * 255))),
)


class MCPPlugin(Gimp.PlugIn):
def __init__(self, host='localhost', port=9877):
super().__init__()
Expand Down Expand Up @@ -3946,8 +3983,7 @@ def _get_pixel_color(self, params):
pixel = drawable.get_pixel(x, y)
# GIMP 3.2: get_pixel returns a Gegl.Color object
if hasattr(pixel, 'get_rgba'):
rf, gf, bf, af = pixel.get_rgba()
r, g, b, a = int(rf*255), int(gf*255), int(bf*255), int(af*255)
r, g, b, a = srgb_bytes_from_color(pixel)
else:
# Fallback: old tuple format (num_channels, bytes_array)
channels = list(pixel[1]) if hasattr(pixel[1], '__iter__') else []
Expand Down
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