Camera1 + Camera2 = Lua

I recently used two cameras to take photos at a soccer game. One with a moderately zoom-y lens (80-200mm) the other with a more zoom-y lens (200-500mm).

When I was looking through the uploaded photos I noticed the time stamps of the two cameras didn’t line up. I’ve seen this before when I have some photos from my phone (which is very smart with time zones and daylight savings) and other photos from an SLR. (much less smart with time zones and daylight savings) Lightroom is very good about letting you select the photos from one camera and offsetting their capture times by a specific amount.

But this is where I made a strategic blunder! I adjusted camera 1 to match the clock of camera 2. Next I went to Lightroom to adjust the times of the camera1 photos. This would have been easy if I knew the delta between the clocks in the two cameras. Sadly I had just destroyed that evidence (by synching the camera clocks.)

So I tried estimating, which was close, but there were a few places where photos from both cameras now had the same capture time, and I was unable to judge from the content whether I needed to increase or decrease the compensation.

I was fairly confident that if I could present the capture times visually (as two data series in a graph) it would be obvious how much I’d need to shift one series to sync with the other series. If only I could extract all the time stamps from both sets of photos, and present them in a graph.

But how do I get all the time stamps of a set of photos in Lightroom? A bit of research taught me I would need to either buy or create a Lightroom plug-in. Being both stingy and keen to learn stuff like how to write a Lightroom plug in, I chose: create!

Martin Fowler has a very helpful page for people that want to create their first Lightroom plug-in. This page also has a line that rings true for me.

“As a programmer, I’m always looking for ways to spend several hours programming to save an hour’s work.”

Martin Fowler

I feel seen.

So I followed the basic arc of Martin’s Lightroom/Lua journey, and was able to extract the needed time stamp values.

For the curious among you, it looked something like this:

I was then able to clean it up and import it into Numbers. (And struggle to get Numbers to show a scatter plot where each series has its own X values. Not intuitive. Thank you YellowBox) And I created a graph like this:

I was definitely going to need to stretch it out, in order to be try out different offset values. Once I stretched it, I was able to shift the blue dots left so that the green dots all fell in gaps.

Of course, next time I’m in this situation I will remember to sync my cameras before I start. And as a fallback, if I do end up using un-synched cameras, I will be sure to fix the photo metadata before I sync the camera clocks.

And for any Lua fans out there, here’s my plug-in code.

local LrApplication = import 'LrApplication'
local LrLogger = import 'LrLogger'
local LrTasks = import 'LrTasks'

local myLogger = LrLogger( 'lightroomLogger' )
myLogger:enable( "logfile" )

local function log( message )
  myLogger:trace( message )
end

local catalog = LrApplication.activeCatalog()

local function findCandidates()
	return catalog:findPhotos {
	   searchDesc = {
			 criteria = "captureTime",
			 operation = "thisMonth",
			 value = 2024-08-04,
	   }
	} 
 end

local function showDates()
	LrTasks.startAsyncTask(function()
		local photos = findCandidates()
		for i, v in ipairs(photos) do 
			-- local prop = v:getRawMetadata("fileSize")
			local createTime = v:getRawMetadata("dateTime")
			local colourName = v:getRawMetadata("colorNameForLabel")
			local createTimeOriginal = v:getRawMetadata("dateTimeOriginal")
			local fileName = v:getRawMetadata("path")
			local result = "orig, " .. createTimeOriginal .. ", " .. createTime .. ", " .. colourName .. ", " .. fileName
			log(result)
		end
	end )
end

showDates()