The layer object have the following extra variables (to be queried using get_misc_value):

image_xres, image_yres, image_colormap, image_guides, image_parasites, name, parasites, visible, active

 Supported options
([
"background":({r,g,b})||Image.Color object
"draw_all_layers":1,
Draw invisible layers as well

"draw_guides":1,
Draw the guides

"draw_selection":1,
Mark the selection using an overlay

"ignore_unknown_layer_modes":1
Do not asume 'Normal' for unknown layer modes.

"mark_layers":1,
Draw an outline around all (drawn) layers

"mark_layer_names":Image.Font object,
Write the name of all layers using the font object,

"mark_active_layer":1,
Draw an outline around the active layer
])

Returned structure reference

class GimpImage
{
int width;
int height;
int compression;
int type;
int tattoo_state;
float xres = 72.0;
float yres = 72.0;
int res_unit;
Image.Colortable colormap;
Image.Colortable meta_colormap;
array(Layer) layers = ({});
array(Channel) channels = ({});
array(Guide) guides = ({});
array(Parasite) parasites = ({});
array(Path) paths = ({});

Layer active_layer;
Channel active_channel;
Channel selection;
}

class Layer
{
string name;
int opacity;
int type;
int mode;
int tattoo;
mapping flags = ([]);
int width, height;
int xoffset, yoffset;
array (Parasite) parasites;
LayerMask mask;
Hierarchy image;
}

class Channel
{
string name;
int width;
int height;
int opacity;
int r, g, b;
int tattoo;
Hierarchy image_data;
object parent;
mapping flags = ([]);
array (Parasite) parasites;
}

class Hierarchy
{
Image.Image img;
Image.Image alpha;
int width;
int height;
int bpp;
}

class Parasite
{
string name;
int flags;
string data;
}


class Guide
{
int pos;
int vertical;
}

class Path
{
string name;
int ptype;
int tattoo;
int closed;
int state;
int locked;
array (PathPoint) points = ({});
}

class PathPoint
{
int type;
float x;
float y;
}

Structure reference

([
"width":int,
"height":int,
"type":int,
"properties":({
([
"type":int,
"data":string,
]),
...
}),
"layers":({
([
"name":string,
"width":int,
"height":int,
"type":type,
"properties":({
([
"type":int,
"data":string,
]),
...
}),
"mask":0 || ([
"name":string,
"width":int,
"height":int,
"properties":({
([
"type":int,
"data":string,
]),
...
}),
"image_data":([
"bpp":int,
"width":int,
"height":int,
"tiles":({
string,
...
}),
]),
]),
"image_data":([
"bpp":int,
"width":int,
"height":int,
"tiles":({
string,
...
}),
]),
]),
...
}),
"channels":({
"name":string,
"width":int,
"height":int,
"properties":({
([
"type":int,
"data":string,
]),
...
}),
"image_data":([
"bpp":int,
"width":int,
"height":int,
"tiles":({
string,
...
}),
]),
}),
])