Convert RGB to HSI (Hue, Saturation, Intensity) instantly — see the formula, the equivalent HSL/HSV values, and a live color preview, all in one place.
I = (R+G+B)/356.86%S = 1 - 3·min/(R+G+B)59.31%H = cos⁻¹(…), adjusted if B > G217.91°How It Works
HSI stands for Hue, Saturation, and Intensity, and it’s calculated from RGB using three separate formulas rather than one shared calculation like HSL and HSV use.
Step 1: Normalize RGB. Each R, G, and B value (0–255) is first divided by 255, giving three decimals between 0 and 1.
Step 2: Calculate Intensity. Intensity is simply the average of the three normalized channels:
I = (R + G + B) / 3
This is why HSI’s Intensity is sometimes called the simplest brightness measure of the three color-space models — it’s a flat average, with no weighting toward any single channel.
Step 3: Calculate Saturation. Saturation compares the smallest channel value to the total:
S = 1 − [3 / (R + G + B)] × min(R, G, B)
When R, G, and B are equal (any gray, including black and white), the minimum equals the average, so Saturation resolves to 0.
Step 4: Calculate Hue. Hue is the most complex part of the formula, since it’s derived from an inverse cosine:
θ = cos⁻¹ { 0.5 × [(R − G) + (R − B)] / √[(R − G)² + (R − G)(G − B)] }
The raw angle θ gives a value between 0° and 180°. A final conditional check determines the true hue: if B is less than or equal to G, Hue equals θ. If B is greater than G, Hue equals 360° − θ. This conditional is what allows Hue to cover the full 0°–360° color wheel instead of stopping at 180°.
Worked example: For RGB(59, 130, 246) — a mid blue — the normalized values are R = 0.231, G = 0.510, B = 0.965. This gives Intensity ≈ 56.9%, Saturation ≈ 59.3%, and Hue ≈ 217.9° (since B > G, the 360° − θ branch applies). The tool above shows this same breakdown live for whatever color is entered — toggle “Show the math” to see each step calculated with the current RGB values.
HSI vs RGB
HSI and RGB describe the same color using different logic: RGB defines a color by mixing red, green, and blue light, while HSI separates a color’s hue and colorfulness from its brightness.
HSI vs RGB. RGB is an additive color model built for how screens emit light — three channels combine directly to produce a pixel’s color. HSI instead isolates Intensity (brightness) as its own axis, so a design or vision algorithm can adjust or analyze brightness without touching the underlying hue or saturation. This separation is why RGB is the default format for displays and code, while HSI is more common in image processing and computer vision, where isolating brightness from color content simplifies tasks like skin-tone detection or shadow removal.
HSI vs HSL vs HSV. All three — HSI, HSL, and HSV — share the same Hue calculation, but their third component differs:
- HSI’s Intensity is a flat average of R, G, and B:
(R + G + B) / 3. - HSL’s Lightness is the average of only the max and min channel values:
(max + min) / 2. - HSV’s Value is simply the max channel value alone:
max(R, G, B).
Because of this, the same RGB input produces three different brightness numbers depending on the model — visible in the “Equivalent HSL” and “Equivalent HSV” values shown alongside the HSI result above. For RGB(59, 130, 246), Intensity comes out to roughly 57%, while Lightness is closer to 60% and Value reaches 96%, since Value is driven entirely by the single brightest channel (Blue at 246).
FAQ
What is the HSI color model?
HSI is a color model that represents a color using Hue (the color itself, 0°–360°), Saturation (colorfulness, 0–100%), and Intensity (average brightness, 0–100%), and it’s most often used in image processing and computer vision rather than in web or graphic design.
Is HSI the same as HSL?
No — HSI and HSL share the same Hue value but calculate brightness differently: HSI’s Intensity averages all three RGB channels, while HSL’s Lightness averages only the highest and lowest channel values, so the two models produce different brightness percentages for the same color.
What is HSI used for?
HSI is used mainly in computer vision and image-processing applications, such as skin-tone detection, medical imaging, and object segmentation, because separating Intensity from Hue and Saturation makes it easier to analyze color content independently of lighting conditions.
How do you calculate Hue in HSI?
Hue in HSI is calculated with an inverse cosine formula based on the differences between the R, G, and B channels, followed by a conditional check — if Blue is greater than Green, the result is subtracted from 360° to place the Hue correctly on the full color wheel.
Can I convert HSI back to RGB?
Not with this tool — this page converts RGB to HSI only. An HSI to RGB converter is planned as a companion tool; for now, use the RGB to HSI converter above to move in the RGB → HSI direction.