crop it like it's hot

For some reason I've created a new Fusion Macro. It's a tool to help match color levels across elements in a composite, and it goes by the catchy name of cropCompare.

cropCompare lets you define two zoomed-in windows on your image to enlarge, visually compare alongside one another, and even graph the values of. It's designed to assist in matching the black levels of two disparate elements in a comp, but it can be used for all kinds of image analyses.

Add the cropCompare node downstream of your comp and view it. You'll see four position controls and two little windows in the lower right of the image.

You have separate Show controls for Crops 1 and 2. For each Crop, you define its location and Sample Size and choose where on the image to overlay it and how big. Put them next to each other and maybe bump up the Gamma the Crops control to make sure your values are matching.

Or, to really make sure, turn on Do Graphs. You now have an RGB graph of the centerline of each Crop. Want to see those graphs unobstructed? Check Do Graphs and Only together.

For the graphs to look their best, please enable Fusion's HiQ mode.

Please give it a try and let us know what you think!

Download O-cropCompare_v2.2 (8kb .rar file)

utecmifpa pt2 — Fusion Usement

The last article was heavy on theory and light on practice. Fusion users, here's a more concrete how-to.

Let's say you have a shot with a Cineon plate, a linear EXR image, and a video-space (sRGB) JPEG. You want to comp them all up real nice in Fusion in linear color space, because you are S. M. R. T.

(to make this example less highly pathetical, get yerself a Cineon plate, a linear EXR image, and a video-space sRGB JPEG, if you don't already have some of your own)

OK, so lin is where you want these images to be, so you'll be looking to the *2lin Macros. We'll chose the straight gamma version of linear for our example.

The EXR is already linear, so it needs no help from us. Add it to your comp with a Loader and display it in a viewer.

It should look dark. Right click in the viewer and select Display LUT > Edit. Enter a Gamma of 2.2. Now the EXR should look correct.

What you have just done is implement a linear color workflow! Crazy.

Now add your JPEG. It has a gamma of 2.2 burned into it. It would look fine in that viewer if we hadn't set the gamma to 2,2. But we did. So let's add a Tools > Macros > eLin_vid2lin tool after the Loader to convert our vid image to linear space. The Macro will promote the image to float automatically in the process.

The only control in vid2lin is Gamma. This value refers to the inherent gamma of the input image. You'll very rarely need to change this from the default of 2.2.

Now the Cineon. Load that puppy into your comp. Fusion will, by default, try to Lin to Log the image for you right in the loader. Bypass this with the Bypass Log to Lin checkbox under the Format tab.

Displaying the log pixels under our 2.2 view LUT will make for a heinously bright image, so add a Tools > Macros > eLin_log2lin tool after the Loader.

There are two controls in eLin_log2lin — Conversion Gamma and Gamma. Both should match the view gamma, so again, you'll probably never mess with the default of 2.2. (The only reason these are two sliders instead of one is a silly omission of publishability in the Fusion Cineon Log tool. The two sliders should always have the same value.)

Now we have linear, log, and vid images all united in one linear color space, and a view LUT that makes them look correct.

Word. Comp away.

Now, when the time comes to output, you need to use the lin2* tools. Tools > Macros > eLin_lin2vid for video space output (such as TIFF, Targa, etc.), and Tools > Macros > eLin_lin2log for Cineon log.

eLin_lin2vid has one control, Gamma, and it really is as simple as a the gamma in a BC tool. Again, you'll very rarely set it to anything other than 2.2.

eLin_lin2log has the same dual sliders as log2lin. You'll never guess what they default to.

If you load a gamma 2.2 image, vid2lin it and then lin2vid it, it will roundtrip unharmed. Same with log and the log2lin/lin2log pair.

The “looks right” state of a Cineon log image (log2lin followed by a lin2vid or the 2.2 view LUT) is based on the standard Kodak conversion with a Dispamma of 1.7/2.2.

Try it. It's way less crazy than it sounds, it will make your work look better, and with the view LUT set to 2.2, you will always know that when things look right in your viewer, they are linear and happy.

Color correction in linear vs. gamma corrected space

A brief example of how simple color corrections behave differently in linear floating point space than in display-corrected space.

image 1

A big reason we color correct with gamma when working in clipped color spaces is that we want to avoid flattening out white parts of the image. This is a valid concern.

image 2

This image is color corrected by multiplying the channels against constant RGB values. This is probably the simplest way to color correct an image, and here the results are quite poor. Subtly poor in how the tonal range is made inconsistent across light and shadow, but profoundly poor in the flattening out of the highlights.

image 3

This image shows roughly the same color correction, but using gamma. Because gamma correction does not affect white, the correction looks much more pleasing. There is also a pronounced contrast change in the image, which some may also consider pleasing, but some may wonder how they could avoid.

Images 2 and 3 were CC'ed in video space, or the raw, uncorrected pixels that we both store and display.

The next two images are CC'ed in eLin. They have been converted to a linear color space and the detail in the blown out window has been preserved.

image 4

Here is a similar gamma correction to the one used in image 3. As in image 3, white remains untouched. But two problems have arisen. Firstly, the linear color space reacts even more abruptly in the contrast and tonal range than the video space image did. The shadows get blocked up and the saturation and contrast changes quite a bit with our adjustment.

but more insidiously, note the darkening layer that I have placed over the window. As with image 3, white remains untouched by the gamma adjustments, But above white we have done a very surprising thing — we have inverted our desired tint.

In this graph of the gamma, or power, function, it's easy to see why. As the gamma curve bends the midtones up and down, it remains pinned at white and pivots there, causing the values above white to go in the opposite direction. So as we gammaed down blue and green, we were pushing values in those channels above 1.0 through the roof!

The scary thing here is that you might not see it at first, and you would go on about your business until you layered something over your windows, or darkened them with some other operation.

image 5

Here we are back to our simple multiplying of the RGB channels, but now we are in linear space with overbrights. Note that we have tinted the image warm without blocking up the shadows, changing the saturation, or altering the contrast of the image. Note as well that the overbright areas react in a very lovely way to the CC.

It's true that when you compare 5 to 3, you may find that some of the “downsides” of the gamma correction in vid space are visually pleasing. The enhanced contrast and variation across the tonal range look a bit sexier than the clean and flat tinting in linear space. But it's important to be able to color correct at a very simple level without getting all this extra artifacting, and this is very challenging in vid space. But in linear floating point, it's no problem at all to add contrast in after a CC.

The other caveat is that we started with an image that had overbrights (an EXR file). Had we not had this extra information in the windows, image 5 would have the same clipped look as image 2.

It's not that you can't ever use gamma correction in linear floating point — you just have to be careful. I've found that in linear space, gamma should be the last thing you adjust, not the first, and this is very different than most peoples' current experience in clipped vid space.

Comparotron2000™:

Multiply in g2.2 clipped
Gamma in g2.2 clipped
Gamma in eLin/LFP
Multiply in eLin/LFP

Mack Row

A couple of Macros I created for Digital Fusion have been posted to eyeon’s new Macro page.

The flexibility of the Macro architecture is a big part of the success of Shake. I hope Fusion can gain a similar following.

And of course I’d love it if After Effects gained Macro functionality someday!