DI (DIGITAL INTERMEDIATE)

Color correction process is done during post production using digital color colorecting software. The term D.I stands for ‘digital intermediate’ which was coined few years back when filming or capturing images done by motion picture film. It was scanned to a digital medium and color corrected then recorded to an intermediate film stock and then it would be processed back to a negative to make prints that would go to theatres.

But now films are shot using digital camera, post processed digitally and presented to theatres again in a digital platform. There is no need for a intermediate but the term Digital intermediate (D.I) still stayed on which should be understood in today’s workflow as ‘Digital color correction’.

Digital Intermediate is a process of color correction done after final editing is performed. For Cinematographers, a software-based non-linear color grading is one of the more exciting, creative capabilities to have emerged from the recent advances in digital technology.

Images are capable of being manipulated to an almost infinite degree in the new digital color correction.

Today’s digital cinema camera images are designed to achieve image quality and color reproduction later through digital color correction. Therefore, DI plays a very important role during the final stages of a film production.

Digital color correction programme is done by a group of technicians comprising of a colorist, conformist and CG.experts.

After final editing is done with EDL, reference video, and complete full resolution rushes of the film is given to the D.I work station.

Conformist will first examine the recorded images in the hard disk and with EDL he will confirm the images to DI time line as per editing order. This process takes around four to five working days.

Then, colorist starts digital color correction programme.

Most of the digital grading facilities are set up like a mini-cinema hall, so that the digital image is displayed on both the computer monitor and projected on the screen. The screen projection allows both the color timer and the cinematographer to make interactive changes and immediately visualize the impact of those changes in an environment that will closely resemble that of the final projection.

However in order for a digital grading solution to be successful, it must be possible to accurately calibrate it. For example, reds displayed in the RGB video color space standard on most monitors look completely different after having been printed to film.

Modern digital grading provides accurate calibration tools that are easy to set up. Facilities with their own color calibration technologies can customize the system to meet their specific needs. Basic calibration commences with the linearization of the display device to avoid distortion of the film color look up tables (LUTs) that will later be applied. This is done using a light sensitive device to measure the intensity of various gray patches that are either displayed on the monitor or projected on a screen.

A correctional LUT is produced that ensures that the display intensity responds linearly to the values of the image – i.e. that the CRT or projector intensity increases in proportion to the color values of the digital image.

Apart from the projector, DI work station is equipped with ‘USER INTERFACE MONITOR’ and COLOR PANEL.

There are different color correction softwares used for Digital film making.

• Lustre
• Scratch Assimilate
• Base light
• Davinci Resolve
• Quantel
• Color

Digital Color correction involves three main stages for motion picture.

• PRIMARY GRADE
• SECONDARY GRADE
• FINAL GRADE

Primary grading:

Primary grade is applied to the whole image and typically used to match the shot or create an overall ‘look’.  Primary colour correction affects the whole image utilizing control over intensities of red, green, blue, gamma (mid tones), shadows (blacks) and highlights (whites) of the entire frame.

The first act familiar with the colorist should be a primary adjustment, cleaning up the shots before grading. If a shot is overexposed / underexposed or if the white balance is wrong, colorist should fix that shot as good as possible within the exposure range. Colorist fix the white balance perfectly by looking to RGB parade and make all the channels equal.

For example: If blue channel is lower than the red and green, then blue channel will be increased with the tools in the software. Usually, it is done by using a simple curve effect with separate red, green and blue channels.
If it is overexposed or underexposed, looking at the waveform or RGB parade, channels are adjusted to bring back or to restore the lost information.
For example, if red channel’s parade is going above the top limit, red channel in a curve effect is taken to bring as much back as possible by pulling the top point of the curve down along the right side. The same is done for underexposed, but now the lowest point in the curve is pushed upwards along the left side.

Most important act by the colorist is to look for ‘Black level’ in the shot. Black level refers to the deepest, darker shadow portion of the image. Adjustments are made by picking the darker area of the image and bring proper black level. If not, the image will appear with ‘milky effect’ or with grains.

The primary color correction is done to make the scene look as neutral as possible.

Secondary Grading :

After primary grading is done, secondary color correction begins and it is the most important stage to alter the image look just as the DOP would have imagined for the film.

Secondary grade, color saturation, brightness, hue, luminance are all emphasized with different color correction tools like

• curve grade,
• masks,
• power windows,
• mattes,
• hue shift,
• motion tracking etc.

In this process many possibilities such as altering sky color & details, day for night, a portion of frame black & white /color, soft skin rendition are performed.

For example: If you want to only alter the skin tone of the artist in a shot, then place a key on the skin tones. By selecting the skins tones and adjust the key until to get a clean selection with only the skin tones. Then start to create the look of the skin that is exactly needed or manipulated. Sometimes it needs to change the hue to make it more correct if the tones are too red or too yellow. Further adjustments like softening, to make it look cleaner or adding contrasts to bring more depth and less flat can be done.
It is all up to the creativity of the DOP on how the product should look.

Final Grading :