irradiation

Japanese: irradiation

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[Sharpness]
The sharpness of a photographic image depends on the performance of the camera lens and the film used to take the photograph, as well as the film development conditions and the printing conditions when making a positive from a negative. In order to improve the sharpness of the final photographic image, it is necessary to examine the entire system from shooting to finishing. In terms of the type of photosensitive material, films using low-sensitivity fine-grain emulsions generally produce images with high sharpness, and even with the same emulsion, the sharpness of the image can be increased by making the emulsion coating layer thinner and taking measures to prevent halation and irradiation (exposure to the edges of the normal image due to reflection and scattering inside the emulsion that has entered the photosensitive layer). A photographic image with high sharpness, or a sharp impression, means that the boundaries between light and dark in the image are clearly defined. When developing film, a method that creates an edge effect (a phenomenon in which the density is higher at the boundary between the high and low exposure areas of the emulsion film and lower at the low exposure area) is used, the contours of the image become clearer and the image becomes sharper.

From [Halation]

...The dyes in the antihalation layer are designed to be decolorized after development. Also, the light that enters the film can be scattered by the silver halide crystals in the photosensitive layer, a phenomenon called irradiation. [Tomoda Yoshitada]...

*Some terminology explanations that mention "irradiation" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

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［鮮鋭度］
　写真像の鮮鋭度は，撮影に用いるカメラのレンズの性能とフィルムの性能のほか，フィルムの現像条件とネガからポジを作る際の焼付け条件などによって異なり，最終的に得られる写真像の鮮鋭度を良くするには撮影から仕上りまでの全体のシステムについて吟味する必要がある。感光材料の品種については一般に低感度の微粒子乳剤を使ったフィルムは高鮮鋭度の画像を与え，また同一乳剤でも乳剤塗布層を薄くし，ハレーションやイラジエーションirradiation(感光層に入射した光の乳剤内部での反射･散乱によって，正規の像の周辺まで感光すること)を防ぐ対策を採れば画像の鮮鋭度が増す。写真の画像が高鮮鋭度を持つ，すなわちシャープな印象を与えるということは，画像の濃淡の境界が明確な状態であり，フィルムの現像の場合にエッジ効果(乳剤膜の高露光域と低露光域との境界で，濃度が，高露光域では一段と高く，逆に低露光域では低くなる現象)を起こすような方法を使うと，画像の輪郭が明瞭になって画像の鮮鋭度が増す。…