Commercial portrait skin dual-frequency separation (Frequency Separation) microdermabrasion retouching: an advanced technique to preserve texture.

1. The fatal drawback of traditional microdermabrasion: Plastic Dummy (Plastic Skin)

In commercial advertisements, fashion blockbusters and high-end portrait photography, the most amateur way to retouch images is to directly use Gaussian blur, surface blur or mobile phone dermabrasion filters to forcefully apply:

1. Mixing of pore texture and light and dark color patches:

• The traditional fuzzy algorithm is a one-size-fits-all mathematical average: while smoothing away acne and spots, it also erases the most precious microscopic pores, furrows, micro villi and hair of human skin**;
• The skin loses all reflective details and becomes a flat texture like plasticine or plastic inflatable dolls, without the warmth and sense of luxury of real life.

2. The underlying mathematical and physical logic of dual-frequency separation: high-frequency and low-frequency decoupling

Digital images can be rigorously split into two independent layers in the spatial frequency domain:

1. Low Frequency - Color & Tone:

• Including the distribution of warm and cool colors in a large area of the picture, the direction of shadows, highlight contours and the uniformity of skin color;
• Determines the facial bone volume and three-dimensionality;

2. High Frequency - Texture & Fine Details:

• Contains high spatial frequency micro-texture details such as pores, tiny acne marks, fine lines at the corners of the eyes, eyelashes, beard stubble, etc.;
• There is no color information at all, appearing as a neutral gray outline relief in pure grayscale;

3. The power of decoupling:

• Repair uneven skin tone, dark circles and facial spots at the low-frequency layer without damaging surface pores!
• Use imitation stamps on the high-frequency layer to accurately remove pimples and pimples without destroying the underlying color and light-dark transition!

3. Photoshop dual-frequency separation action precise creation process (8-bit and 16-bit algorithm formulas)

1. Create base layer:

• Duplicate the background layer twice and rename it to Low_Frequency (low frequency) and High_Frequency (high frequency) respectively;

2. Process low frequency layer:

• Hide the high-frequency layer and select the low-frequency layer;
• Execute Filter -> Blur -> Gaussian Blur;
• The golden rule for setting blur radius: Zoom in to observe the skin and slowly increase the radius until the microscopic texture of the pores is just barely visible, but the outline of the facial features is still clearly discernible (usually between 3 and 8 pixels).

3. Processing high-frequency layers (extracting details):

• Turn on the high-frequency layer display and select it, execute the menu Image -> Apply Image (Apply Image);
• For 8-bit depth images (8-bit JPEG/TIFF):
• Layer selection: Low_Frequency;
• Blending mode: Subtract;
• Scale: 2;
• Offset: 128;
• (Principle: High frequency = current layer - low frequency layer + 128 neutral gray)
• For 16-bit depth images (16-bit Pro RAW):
• Layer selection: Low_Frequency;
• Check: Invert;
• Blending mode: Add;
• Scale: 2;
• Offset value (Offset): 0;

4. Hybrid Restore:

• Change the layer blending mode of the high-frequency layer to Linear Light;
• At this time, the picture appears in a complete form that is 100% identical to the original image, and the dual-band separation system is established!

4. Independent refinement of high and low frequency practical techniques

1. High-frequency layer detail purification (Texture Clean-up):

• Select the high-frequency layer and select Clone Stamp tool (Clone Stamp);
• The sample attributes are set to: Current Layer (Selecting "Current and Lower Layers" is strictly prohibited!);
• Opacity and Flow set to 100%, Hardness set to 70%;
• Hold down the Alt key to draw on healthy pore skin, and tap lightly to cover acne, closed pimples and peeling skin;
• Blemishes evaporate instantly, while the surrounding pore structure is seamless and absolutely realistic.

2. Low-frequency layer skin color light and shadow reshaping (Color Blending):

• Select the low-frequency layer and use the Mixer Brush tool;
• Settings are: Clean Brush, Wet 20%, Load 20%, Blend 20%, Flow 20%;
• Gently apply and spread along the highlights of the human facial muscles and bones;
• The original uneven cheek redness, blue eye bags, and mottled light spots are gently smoothed and resolved, making it transparent and even like a top makeup artist applying liquid foundation, while the high-frequency layer above still firmly locks the hair-level pore texture!

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