François Tarlier's Blog > CG Artist, Matchmover, VFX, Open Source topics, Computer Vision, and geek stuff !

This one should be pretty simple, but still all the shaders I have found on the Internet was based on conversion to HSL color space. Which could be actually useful if  you need some color balance control, but if you just want to control the saturation as fast as you can, it’s probably not the right approach.

Anyway here is a small shader which does the trick (Media Player Classic) :

http://www.pasteall.org/8891/c

The goal here was to understand how works the Exposure feature of Photoshop for my research on lift/gamma/gain

NB : I wouldn’t say I’m an 100% sure about how it works, but that’s how I understood it worked so far

Exposure :

I though exposure was more complicated than that (maybe it is) but the way I’m reproducing it, is only by adding a percentage of the pixel by himself. nothing more complicated than that.

Offset :

As seen in my previous post, the Offset is just an Add of a value. My first approach on it was saying Offset is controlling the luminance of it, so I guess the correct way would be to convert the pixel in the YCbCr color space, add a value to the Y channel, and reconverting back to RBG color space. But this is doing a lot of calculation for nothing, while adding just a value to the entire picture would probably do the same, and actually would correspond to the Lift (or Offset of the CDL).
Plus switching between color space makes you loose some tiny precision in the color.

Anyway, I’ll give the two solutions, please let me know if you think one is better than the other

Gamma :

As usual, power(1/gamma)

The right order :

If all this was actually all pretty simple, at least I learned one thing (obvious as well I must say). Don’t forget to do the operation in the right order. In my first try I had a small bug, and couldn’t have the same result in Photoshop & in my shader, because I was doing the offset before the exposure. Which is pretty silly, since if you do that, you are loosing all the dynamic range of your picture when you actually want to have as much information as you can for your exposure.

The order is Exposure -> Offset -> Gamma.

Formula :

output = ((input*exposure) + offset)^(1/gamma)

hum… looks a lot like the CDL formula doesn’t it ? Except exposure is a single float value between 0 and 20 ? (maybe more, maybe less depends of your picture)and the default value should be 1.The offset should be between -10 ? and 1 I think.

Shaders (HLSL in Media Player Classic) :

http://www.pasteall.org/8868/c

Here I’m giving the version with YCbCr conversion, but I’m pretty sure it is not doing anything more than the above one, except loosing information in conversion. But at least it shows the YCbCr conversion

http://www.pasteall.org/8869/c

Following my previous post “lift-gamma-gain color correction formula with blender compositing” I continue my research about all those formulas.

Comparison

I came to compare the ASC CDL (American Society of Cinematographers Color Decision List) formula to the Lift/Gamma/Gain formula I found on Blender.org

Here are the results :

Where the formula are :

• CDL : ((input*slope)+offset)^(1/gamma)
• Lift :  gain * (input + lift * (1 – input)^(1/gamma))

(slope = gain ; offset = lift)

You can see that CDL is able to burn (exposure) the white, while the Lift will keep the white unchanged as much as it can.
_dbr did a nice test for me in Shake and create a graph that really shows the differences

so in both formula by only changing Lift/Offset, you can see clearly that the lift keep the white unchanged while CDL push the black and white as well.

HLSL Shader in Media Player Classic

Yes, in Media Player Classic, you can write shaders compiled in runtime while you are watching your favourite TV Shows ^^ . Awesome !!!

hlsl code on Pasteall.org

Conclusion

So I guess CDL is much easier to use, but I believe that Lift could give you much control other the image. What would need Lift to be able to push the white as well would be an exposure parameter! (which is the goal of my next shader )

I’m currently taking a class at Fxphd called “DOP210 -DSLR Cinematography” with Stu Maschwitz (prolost) & Mike Seymour as mentors!
This is an awesome class if you have a Canon 5D or a Nikon D90 and want to make movies with it and post-production/grading as well!
Either if the class is talking about the two cameras, the focus is mainly on the 5D!
Stu had a really nice post on Prolost about setting the 5D called “Flatten Your 5D“. Those settings aim to get a neutral picture (low contrast, low sharpen, low saturation,…) which would give a better control in post-production for grading. Settings which he’s using in his class of course !
Since I own a D90, I thought I would give a try to port his 5D’s settings to the D90!
Here is what I have done :

I also turn off D-Lighting, but I’m not sure it is the right move. I’m not sure it is the best settings yet but it looks close though

Update : Also I recommend you to take a look at “Understanding and Optimizing the Nikon D90 D-Movie Mode Image“ on the DVXUser Forum, it give nice tips to trick your camera a bit

Here is a test I have done with those settings and Rebel CC on After Effects.

Mobile Version on Vimeo

I found out a nice Flash application which can help you to understand the concept of F-Stop, Shutter Speed and Exposure and how it affects your shoot.

You can try it on DryReading.com here : http://dryreading.com/camera/index.html

CameraDemo : Flash Application which let you play with ISO, F-stop, Exposure, ..

This is a new “SpareTime Project”, playing (and testing) with Microsoft PhotoSynth.

Photosynth creates an amazing new experience with nothing more than a bunch of photos. Creating a synth allows you to share the places and things you love using the cinematic quality of a movie, the control of a video game, and the mind-blowing detail of the real world.

Most likely all you have to do is to take hundreds of picture, load it in PhotoSynth and it will automaticly stitch it together in 3D space

This is my first attempt by taking picture of Montpellier Antigone. So far I tried to re-create the path of the entire Antigone. But I guess I didn’t took enought picutre (about 400 photos) so it couldn’t stitch some different part together.

You will need Silverlight to test it or PhotoSynth plugin for the DX version. (damn Microsoft … couldn’t use Flash like everybody >_<)

Related Link :

• SpareTime Project Page
• My Synth page of Montpellier Antigone

Last week-end was the FISE at Montpellier, so it was a good reason to go and shoot some photos and videos. I guess this could be a “Spare Time Project” as well. I did learn a lot by shooting sport photos ! It is way harder than what I thought. I did use some old optics on my D90 so, aperture, shutter, and so on totally manual, but it’s a really nice way to learn.

Basically this is what I learned :

• Think fast
• Set your camera when nothing happen
• keep your two eyes open (one in the camera, the other one on the field)
• understand what the riders are going/want to do
• always stay aware of what happen
• look every where
• know your gears !

all those things are quite common, and actually that what I mostly do every time I take a picture, but with, what I would call, high speed shooting those things are way more intense !!

FISE 2009 – a set on Flickr.

3 new pictures on Flickr

Love the woman, Love the camera !!!Wish I had the same … camera

Ok let’s be honest here, she is hot, pretty and all that stuff, but hey! would this movie look the same without the “Red One”?!? :p  I have seen videos from the last NAB that shows the second generation of Red camera coming soon. Which hopefuly will drop off the price of the first generation. For now my D90 will do ^^

Anyway just sit and watch my friends :

"Good Morning Megan Fox" Video by by Greg Williams on the Red One camera

From bed to bathing suit, spend a day with Transformers star Megan Fox in this film shot for Esquire by Greg Williams on the Red One camera.

The cover of the next Esquire was shoot with the Red camera as well, you can see it here with all the process and the Photographer background : http://www.esquire.com/the-side/video/megan-fox-images-0609

Rainbow @Mauriac (2), originally uploaded by François Tarlier.

rainbow after a storm @Mauriac.
The light was really strange, it was really looking like on the picture. so weird, so pretty. The sky was grey, just a small amout of light colored the scene and this green just popup like that !