# Image Placement

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If you’re using ConTeXt for complex layout tasks, you need to calculate with image sizes. Often it makes sense to use Lua functions.

Beware, TeX calculates internally in "scaled points" (sp), 1 sp = 1/65536 pt.

## Measures in pure ConTeXt

You can get at a picture’s dimensions with one line of TeX code:

```\setupexternalfigures[location=default] % necessary to find pictures in tree
\getfiguredimensions[hacker.jpg]
```

This defines a bunch of variables:

## Calculations in Lua

```TEXpt = 65536 -- sp per pt
TEXptpi = 72.27 -- pt per inch

function sp2mm(n)
-- convert sp into mm
return math.floor(n * 35.28 / TEXpt)/100
end

function glue2num(glue)
-- convert TeX glue (e.g. skips) into dimensions(? or numbers)
return glue.width + (glue.stretch * glue.stretch_order) - (glue.shrink * glue.shrink_order)
end

function ImgSize(resolution)
local filename = figures.current().status.fullname -- current image
local pic = img.scan{filename = filename}
local picH = pic.ysize * TEXptpi * TEXpt / resolution  -- picture height in sp
local picW = pic.xsize * TEXptpi * TEXpt / resolution  -- picture width in sp
context("height=" .. picH .. ",width=" .. picW)
end
```

## Postponing

If you want to place full page images or similar content on distinct pages, try the postponing mechanism:

```\definemakeup[fullpage][
page=no,
doublesided=no,
% footerstate=empty,
pagestate=start,
]

\startpostponing[pagenumber]
\startfullpagemakeup
% use \setlayer & friends
\stopfullpagemakeup
\stoppostponing
```

The pagenumber argument can be absolute or relative, e.g. 23 or +2. Values like +0 or -1 might fit your usecase.

((WORK IN PROGRESS))