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What is LOG?

Converting the amount of exposure numerically with the sense and feeling of a natural human touch.“Linear”only expresses the absolute degree of brightness in integer LOG provides the ability to convert the exposure level numerically in a way that’s more pleasing and closely matches human vision.The most beneficial point of using a LOG image is to maximize the wide dynamic range that cameras may have while fully maintain the reading accuracy for dark areas and maximizing the information in highlights over 100% At the same time, it enables a user to create a unique and bold Look image.

LOG image basic lesson

Hi, everybody. This is Uchida from TVLogic.
On the following pages, I would like to provide some lessons about motion picture production using LOG images.

These are some of the topics:

  • First of the all, what is a LOG image?

  • I want to produce motion pictures using LOG images, but do can I do it?

  • I am producing motion pictures using LOG images, but how can I improve the efficiency and quality of the process?

I hope to answer these questions and solve your problems.

INDEX

※The contents of this lesson are subject to change.

Distinctive FUJIFILM LOG application

Lesson 4: Why do LOG images look dull?

Hi, everyone. I'm Mitsuhiro Uchida from TVLogic. In the last lesson, using the concepts,
"Scene referred images" and "Output referred images",
I explained the following:"Most image signals are scene referred images when they are produced. After some conversions are done, they become output referred images", "Output images are displayed on the corresponding display directly."

I hope you understand from these concepts:
"Scene referred images are not produced with the intent to view on a display."

In this lesson, I will explain about "Why do LOG image look dull?" and unfold the concept: "Some conversions".

What are

What is the

Well, what are "some conversions" that are able to change scene referred images to output referred images?
What kind of conversion will make scene referred images into output referred images?

Let's take a look at the example of movies shot on film.

Original scene→Negative films (Negative concentration)=Scene referred images Printing→Some conversions Positive films→Output referred images

In motion picture films, "Some conversions" are done during the printing process.

To achieve better quality of images, improvement of both negative and positive films for movies was done continuously in the motion picture production industry.
The know-how to project high quality images onto a screen is crystallized in the printing process (some conversions).
This includes characteristics of each negative film, film processing, characteristics of each positive film, and other elements.
All of them are consolidated and the positive release print for the motion picture is made.


In the motion picture production industry, more than 100-years of know-how are crystallized into the characteristics of the negative and positive films, and print processing that will be used. And all of them contribute to making high quality images.

What is

What are "some conversions" that are done during the printing process of movies digitally shot in current image production?

A few examples of "some conversions" that are done during image production currently:

  1. ① Displaying through film previewing LUT with grading software.
    Film previewing LUT is "Some conversions" in this case.
    Normally, in this case, the film printing process does this conversion; therefore, here this conversion is "film color reproduction done by digital emulation."

  1. ② Shooting video gamma, and outputting image signals from cameras.
    Video gamma is "Some conversions" in this case. Usually, this process means only scene referred images are converted and adjusted using only the gradation characteristics of monitors; therefore, it doesn't lead to preferable image reproduction.

  1. ③ Previewing LOG images with onset grading. In this case, "Onset grading" is "Some conversions.
    "The DIT is viewing and evaluating the images and processing them with color adjustments so that they will more closely resemble the final images.

Let's analyze and look into the elements of

Those were some examples of "Some conversions". Now, let's analyze and look into the elements that make up "Some conversions".

Now I see: many conversions have been done to make scene referred images into output referred images.

We can categorize the elements that we call "Some conversions" into the following categories:

①Gray scale conversion ②Color conversion ③Device dependent conversion

"Some conversions" are combinations of these ①②③.
We call this combined conversion "Rendering".

I will summarize each conversion as follows.

①Gray scale conversion Images have finite dynamic range in the original scene.By capturing images with the sensor of the camera, the dynamic range will be narrowed down; however, cinema cameras nowadays have very broad dynamic range. On the other hand, the dynamic range of the displays has limitations; therefore, we need to limit (compress) the range of the image.Also, outdoor brightness during daytime is very high. It is impossible to reproduce the absolute value of that brightness.When we reproduce images with display brightness lower than the original, we feel the contrast (gradation) is poor.Then, some adjustments are done to alter the gradation and reproduce the images as close as possible to the original contrast of the scene.
②Color conversion Basically, it is important to reproduce the original color, but the conversion that is preferable when viewed in the display is done.For instance, in reproduction of the original color, memory colors are preferable, such as human skin color, blue sky, and green in nature. However, depending on the scene, significant color correction might have to be done to depict the emotion of the scene and characters.
③Device dependent conversion The last part of conversion is a process of converting into signals that can be output on the displays.This aims to convert into the code values that can be input to the display. After being pre-processed, adjustments to constrain the image into the dynamic range of displays or color reproduction range, primary color conversion, white point conversion, and gamma conversion, etc. are done. Lastly, it will be converted into integer code values, such as 10 bit.

By the way, we should talk a little about ACES standard.
The ACES standard was established to standardize the color control of digital image production.
As a matter of fact, this structure utilizes the concept of scene referred images, rendering, and output referred images.

ACES standard

The above diagram I often use when I explain the ACES standard.
This can be summarized by saying that from cameras to ACES is scene referred, then RRT is for rendering, and all further processes are output referred.
By categorizing and separating these three processes, it enables a highly flexible workflow that does not depend on the devices being used.
In a future lesson, I will further explain about the ACES standard separately.

In our next lesson, I will analyze and explain about Sony's F55 SLOG3 in complete detail. Please join us!

Mr. Uchida's profile

He refers to himself as an expert problem solver in image system designs. Starting his career with consumer photos, Mr. Uchida was involved in designing systems using LOG images since 1995 predating the release of Cineon. Currently, he devotes himself enthusiastically to creating solutions which maximize a camera's full feature set with ease.

Distinctive FUJIFILM LOG application
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