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Chapter 1 — fondamental
Pixel and Resolution in Underwater Photography
Understand what a pixel is, how resolution affects your underwater photos, and why more megapixels don't always mean a better image.
What is a pixel?
A pixel (short for picture element) is the smallest unit of a digital image. It is a single point, usually square, that contains color and brightness information.
Imagine a mosaic: each tile is a pixel. Assemble millions of these colored tiles, and you get a photograph. The perception of a continuous image is an illusion created by the small size of pixels and our eye's ability to combine them.
Key definition: A pixel encodes a color value (via the RGB model) and brightness. It is the combination of millions of pixels that recreates the visual richness of a scene.
Underwater Application
Underwater, each pixel counts more. Light scattering reduces the overall contrast of the image, which means that the individual quality of each pixel (its signal-to-noise ratio) is even more critical than on land. A sensor with larger pixels will capture more light in the dark conditions of the depths.
Resolution: The number of bricks
The resolution of a digital image corresponds to the total number of pixels it contains. It is expressed as width x height (for example, 6000 x 4000 pixels) or in megapixels. The higher the resolution, the more detail the image can reproduce.A 6000 x 4000 pixel sensor produces 24 million pixels, or 24 megapixels (MP). High resolution allows for cropping without noticeable loss of quality, a valuable advantage in underwater photography where it's not always possible to frame perfectly.
| Resolution | Megapixels | Typical Use | Cropping Possible |
|---|---|---|---|
| 4000 x 3000 | 12 MP | Social media, web | Limited |
| 6000 x 4000 | 24 MP | A3 print, moderate cropping | Comfortable |
| 8000 x 6000 | 48 MP | Large format print, intensive cropping | Important |
| 12000 x 8000 | 96 MP | Advertising, gallery, archiving | Extreme |
Key Takeaways: Resolution is important but not sufficient. A 200-megapixel sensor with poor optics is worthless. The entire optical system determines the final quality.
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Frequently asked questions
Combien de megapixels faut-il pour la photo sous-marine ?
Pour la majorite des usages (web, reseaux sociaux, tirages A3), 20 megapixels suffisent largement. Au-dela, l'avantage est principalement le recadrage en post-production, utile pour les sujets difficiles a approcher sous l'eau.
Quelle est la difference entre resolution et qualite d'image ?
La resolution indique le nombre de pixels, tandis que la qualite depend aussi de la taille des pixels, du traitement numerique, de l'objectif et des conditions de prise de vue.
Pourquoi mes photos sous-marines semblent-elles floues malgre une haute resolution ?
Le flou sous-marin provient generalement de la diffusion par les particules, d'une mise au point faussee par la refraction, ou de vibrations dues au courant. Se rapprocher du sujet est la meilleure solution.