Camera Profiling with Darktable-chart

Aloha and welcome to another episode of Weekly Edit Things have been getting a little busy around here

I wasn't able to get to an episode last week, but I've got a good one this week I'm looking at color profiling my camera A couple episodes ago I looked at making Base Curves, which basically tries to match your RAW image to your in-camera jpg in terms of the L Channel, the luminosity This week I'm using an it8 target, which is a color chart, and I'll use an application called darktable-chart to map the color patches on the RAW image out of my camera with the in-camera jpg There are a couple things we need to do in order to make this happen

You'll have to pay the money and get a good target There are some cheap ones out there and they have terrible reviews People say they just don't work Evidently the inks on this target are supposed to be such that they maintain their reference proportionality to each other under a variety of lighting conditions, but nonetheless, they recommend that you shoot this target in mid-day sunny conditions It was a little cloudy, and it's hard to get a sunny day around here, so we're doing this episode with the best I have

I've noticed that I get better results if I match the ISO My color profiling changes a little bit with ISO, so I'm going to take the time personally and shoot at different ISOs and make color mappings for each ISO, just like I did with base curves What we want to do is have a RAW and a jpg of our color target, so you'll have to change in your camera to do that And I want to have the white swatch down here be around an L92 So, I shot at a variety of exposures and then I'll use the Color Picker tool on Mean and look at the luminosity

This one is around 90 and I shot this one at 1/20th of a second This one here I shot at 1/15 second Let's see what the L value is on that one That's 98; that's a little hot I'm not going to use that one; I'll use the previous one

Now, notice my History is blank: SUPER-IMPORTANT So, we'll use this one and the matching jpg This is ISO 100 We'll generate a Color Lookup Table mapping that will match these two I'll label this when I'm done with the name of the camera body, so that profile is determinate, and the ISO

Then, when I'm done with this big project, I'll have made a value for each camera body and each ISO that I shoot at Maybe I'll break it up a little bit, but I want to have various values; I don't want to just have a couple Okay, I'll crop this I don't have to, but I find it easier to work in darktable-chart if this is cropped a bit first I don't need to worry about keystoning here; I can fix it later

I want to apply a similar crop to my jpg so I'll copy and paste this over all of these There we go Now there are two places I can set the Output Color Profile I'm going to want to do that because I was getting indeterminate results when I only set it at the Export function So, I'm setting this in Output Color Profile to Lab and I'm setting it in the Export Settings to Lab

So, File Format is pfm The reason we're converting this and the jpg to pfm is that's the file format the darktable-chart program wants to see the files in Profile is Lab; Intent is Image Settings I'll Export that one Then I'll take this jpg and set it up as Lab, and set its Export to Lab also

Okay, something I forgot to go over: there's an rc file associated with Darktable that requires an entry in order for that pfm output using the Lab color space to work properly That's located in config/darktable/darktablerc and it's this line right here: allow_lab_output=true If you put this line in this file while Darktable is open, then Darktable will over-write this rc file when Darktable closes That's how it stores whatever session options you set So, you need to make sure you close Darktable first, open this rc file, add that line, close it, and then you can open Darktable again

This part here, where I exported these as a pfm only worked because I had added that line previously This is the one I ended up buying I got this one in the little plastic case because I could include it in my camera bag I found that, if I took a shot of this and used it with my white-balance tool, I got pretty good results for adjusting my white balance So, it seemed like it was convenient to take with me

There's also an 18% grey card on the next page over, and it's all plastic, so that seemed like the best one Okay, I'm going to need this cht file What the cht file is, is it's information about what colors are located where on that Color Checker Passport

I'll include a link to this file in my webpage at weeklyeditcom Also, you can just look around the internet and get it Okay, now we'll open darktable-chart This has three tabs: Source Image, Reference Values, and then Process makes the mappings So, on the first tab there's two places: Image and Chart

And it's a little different on the Reference Values; you'll see Okay, so we made those pfm files This was the first one This was my RAW image Then I'm going to apply that chart file

See, it's just got these squares and it's got reference colors We grab the corner and align it so that the little squares inside the bigger squares only touch the colors that they're supposed to; they don't touch any of the edges That is pretty important If you need to, to get it to work, you can adjust the Size of the squares This is a little backwards: the lower you make this Size, the bigger the squares, and the larger the Size, the smaller the squares

You pretty much want to make the squares be as big as possible but not have them touch any of the edges That looks pretty good I'm good and safe there Then, on this next tab, Reference Values, here is where we align the jpg So, where it says Mode, we have to change this

We go to 'color chart image' Then this time we select the file on the right-hand side instead of the left So, under Reference Image, we'll pick the pfm of the jpg Then we have to align this one too There we go

I'm double-checking all my squares Look at them and make sure none of them — like, see, this one is on the edge and that one is on the edge, but they look okay Then I go to Process: 'patches with gray ramp' There we go I like this one: SAT1SAT8 'number of final patches' – I did not get good results at 24; I thought 48 was much better And then 'process', and it goes And now 'export' We'll save these

and they save them as 'styles' Now we can go into Darktable Under Styles in the Lighttable view, Import, and there we are There's our style Now we'll apply that style to an image This one was shot at 100 ISO

Okay, so we click on the image and we double-click on the style Alternatively, you can open the image and go down here and select the style, and it will apply it See what it applied here? It applied a color lookup table entry and a Tone Curve entry Let's look at the jpgs right next to it Here's the jpg, okay, and here's the RAW with the changes made

It looks pretty good It looks kindof close; it's not perfect The L Channel looks like it could use a little work, but the colors are close, and it's a lot better than the original RAW There's the original RAW and the jpg, and here's with the changes So, here's what we can do

We can come over here to Color Look Up Table and we can say 'store new preset' I'll call it my camera body name and the ISO Then it will auto-apply this each time Oops – one change there: only RAW images There we go There's also an entry here under Tone Curve, and I would do the same thing: I would set a pre-set and tell it to auto-apply

You can see this one didn't use the Base Curve, because the Base Curve is specifically set (off) and it makes the changes in the Tone Curve instead Okay, that was at 100 ISO; let's find one at 3200 ISO, because I said I wanted to do these for various ISOs This should go a lot quicker Now, we're looking for the white here to be around 92, so I take my Color Picker and I check it That one's at 73; that's not even close

Okay, this one was shot at 1/1000 second and this one at 1/800, this one at a 1/640 Oh, that's better; it's up to 87 This next one here was shot at 1/500 second Let's see that one These are generally going to run around +1 to +2 on your exposure

That one's at 95; I think that's fine Let's use that one Don't forget: we've got to go in here and change our Output Color Profile to Lab, and same thing with the adjacent jpg We'll take these two and make a pfm So: PFM; Lab; Image Settings: go! Okay

Now we'll change this pfm image to this new one we just did I know this is silly, but you've got to re-select this If you don't, at least on my version, it won't give you this option at the end to 'process' So, I re-select it, and then re-align it I make those squares a little bigger by pulling this slider down Make sure I'm not over the edge anywhere; this is a little close, so I'll pull this end up a little

Check all your squares Make sure they're all good Okay, we're good Now we go on to the second one, which is the one we made from the jpg, and then align this again We'll make these squares a little bigger too

Are they all good? Everything's good? Oh, that one's close; let's pull that up a little Okay, we're good everywhere Then we go to Process: SAT1SAT8; 48; hit 'process' and then 'export' Okay Now we'll come in here in Darktable Go to Styles; Import, and our new style should be there This is the one for 3200 ISO so we'll apply it to this image here which was shot at 3200 ISO Then when we look at it and the jpg, they look pretty close too

Here was our original and that's the jpg Here's with the changes made, and there's the jpg; that's pretty close too But, I have found that I can get even closer The way I can get even closer is by applying the custom Base Curves that I built in a previous episode, before I export this RAW as a pfm So, let's give that a shot

I want to warn you, it specifically says that you're not supposed to do this in the Darktable manual But I get better results, and I'm interested in results, so that's what I'm going to do We'll change this back to RGB and we're going to apply the Base Curve to this that's appropriate for 3200 I think 5000 is probably the right one Okay

Now, this is important: you've got to re-check your L level after the Base Curve And look: we're up at 99 Not good! Okay, so we've got to go back to one that had a faster shutter speed because we're applying the Base Curve now So, the previous one was shot at 1/640 second Let's apply that Base Curve again and check it

97: we're still way up there So, let's go way back to this one Here we are: 1/1000 second Apply our Base Curve and check it: 92; that's pretty close So, we're going to take this one, we're going to change the Color Output to Lab

We're going to go to the next image, which is the corresponding jpg; we're going to change it to Lab We're going to take this two, export them as pfms There we go: Bingo! Go into this program, and we'll knock this thing out Source Image There we go

Oh, I forgot: I've got to re-import this Otherwise, I will just be wasting my time Don't forget: what's different with this one is we started by applying the Base Curve image to it I'm checking all of my squares Okay, now the corresponding jpg to this one

I'm checking all my squares to make sure they're exclusively on the color I want Okay, that all looks good Now: Process There we go, and 'process' and 'export' Now we will take the shot I took at 3200 ISO and apply that style to it So, we'll need to import it and we need to apply it by double-clicking on it

Now, this time, remember we added the Base Curve before we exported it as a pmf, so we need to re-add that Base Curve to complete the calculations here There we go That's the jpg and that's the RAW with the Base Curve applied first They are very, very close Wow, that was a lot

Everybody, have a great week You can refer to the show notes, and I'll try to include relevant information there See you all later Bye