| Les deux révisions précédentesRévision précédenteProchaine révision | Révision précédenteProchaine révisionLes deux révisions suivantes |
| issue153:krita [2020/02/11 08:24] – d52fr | issue153:krita [2020/02/11 08:53] – d52fr |
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| Au point où nous en sommes, notre image résultante : | Au point où nous en sommes, notre image résultante : |
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| | Si nous consultons notre nouvel histogramme, nous pouvons voir que la majeure partie de l'image a des couleurs réparties sur tout le spectre, alors que le ciel est toujours réduit à un seul pic aigu à droite. Ce dernier point ne présente pas de modification majeure par rapport à l'état original, alors que la partie principale est plus équilibrée qu'avant. |
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| **So far, our photo has progressed quite a bit in quality in comparison to the original. However, one aspect is lacking to give the scene a tad more realism: colors. These were lost during the initial photography, when the black-and-white negative was exposed. In a broad sense, the chemicals spread over the glass plate were sensitive only to the general light intensity falling on them. Information was lost concerning the exact wavelengths. In more recent color photographic film, several layers of sensitive chemicals inter-spaced with filters allow retaining information on separate colors on, at least, three different wavelengths. Thus, a (rather good) approximation of the scene’s original colors may be recomposed after processing, making positive copies and development. In our case, however, this color is completely lost to us. In digital terms, what we now see as a level of gray coded 200 on a range of 0 (black) to 255 (white) shows up as a light gray. It is possible that the original color in the scene was a light gray, with red, green and blue values of 200, 200 and 200 and with average intensity 200. But the original color could very well have been 250, 200 and 150, a light salmon color due to the presence of more red and less blue. It could also have been 150, 200 and 250, a light pastel blue, or any other variation of primary colors giving the same average intensity of 200.** | **So far, our photo has progressed quite a bit in quality in comparison to the original. However, one aspect is lacking to give the scene a tad more realism: colors. These were lost during the initial photography, when the black-and-white negative was exposed. In a broad sense, the chemicals spread over the glass plate were sensitive only to the general light intensity falling on them. Information was lost concerning the exact wavelengths. In more recent color photographic film, several layers of sensitive chemicals inter-spaced with filters allow retaining information on separate colors on, at least, three different wavelengths. Thus, a (rather good) approximation of the scene’s original colors may be recomposed after processing, making positive copies and development. In our case, however, this color is completely lost to us. In digital terms, what we now see as a level of gray coded 200 on a range of 0 (black) to 255 (white) shows up as a light gray. It is possible that the original color in the scene was a light gray, with red, green and blue values of 200, 200 and 200 and with average intensity 200. But the original color could very well have been 250, 200 and 150, a light salmon color due to the presence of more red and less blue. It could also have been 150, 200 and 250, a light pastel blue, or any other variation of primary colors giving the same average intensity of 200.** |
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| | Jusqu'ici, la qualité de notre photo a progressé un bon peu par rapport à l'original. Cependant, une aspect manque pourdonner à la scène un peu plus de réalisme ; les couleurs. Elles ont été perdues lors de la prise de vue, quand le négatif noir-et-blanc a été exposé. Au sens large, les émulsions chimiques sur le verre n'étaient sensibles qu'à la seule intensité de la lumière qui les atteignait. Les informations sur les longueurs d'ondes réelles ont été perdues. Dans des films photopgraphiques plus récents, plusieurs couches d'émulsions sensibles séparées par des filtres permettent de retenir ces informationssur les différentes couleurs pour, au moins, trois longueurs d'ondes différentes. Ainsi, une approximation (plutôt bonne) des couleurs de la scène originale peut être recomposée après traitement, en faisant des copies positives et un développement. Dans notre cas, cependant, ces couleurs sont complètement perdues pour nous. En termes numériques, ce que nous voyons maintenant comme une valeur de gris codée 200 sur une étendue allant de 0 (noir) à 255 (blanc) montre un gris clair. C'est possible que dans la scène originale, cette couleur était un gris clair, avec des valeurs de rouge, de vert et de bleu valant 200, 200 et 200 et une intensité moyenne de 200.Mais la couleur originale pourrait très bien être 250,200 et 150, un pastel bleu léger ou une autre variante de vcouleurs primaires dont l'intensité moyenne serait aussi de 200. |
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| **Our takeaway here, is that in order to colorize our image, we will need to add back the information that has been lost. Luckily, our experience as humans tells us that the sky should probably be blue, and the trees green. | **Our takeaway here, is that in order to colorize our image, we will need to add back the information that has been lost. Luckily, our experience as humans tells us that the sky should probably be blue, and the trees green. |
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| To finish up for today, let us add in Krita a new transparent layer. We will also need to convert the image from gray-scale to color. To do so, choose menu option “Image”, and “Convert image color space”. Set it to “RGB/Alpha”, i.e. three color channels (red, green and blue), plus an alpha (transparency) channel.** | To finish up for today, let us add in Krita a new transparent layer. We will also need to convert the image from gray-scale to color. To do so, choose menu option “Image”, and “Convert image color space”. Set it to “RGB/Alpha”, i.e. three color channels (red, green and blue), plus an alpha (transparency) channel.** |
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| | Notre conclusion ici, c'est que pour coloriser notre image, nous aurons besoin de lui redonner les informations qui ont été perdues. Heureusement, notre expérience d'êtres humains nous dit que le ciel sera probablement bleu et les arbres, verts. |
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| | Pour termeiner aujourd'hui, ajoutons dans Krit un nouveau calque transparent. Aurons aussi besoin de convertir l'image de l'échelle de gris en couleurs. pour ce faire, choisissez les options de menu « Image », puis « Convert image color space » (Convertir l'espace de couleurs de l'image). Réglez-le sur « RGB/Alpha », c'est-à-dire trois canaux de couleurs (rouge, vert et bleu), plus un canal alpha (transparence). |
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| **Now, with the airbrush at a low opacity setting (about 0.2 should give good results), and rather broad opening (perhaps in the range of 40 to 300 pixels, depending on overall image size), let us brush in some color. Unlike in the first part of this series, when we were covering up small defects, now we will need to proceed with wide open strokes giving coverage to large areas at once, but with little density. For our first attempt, we will be using just three colors --a light blue, a darker green, and a reddish brick pink-- and not worrying about complete coverage of each part of the scene.** | **Now, with the airbrush at a low opacity setting (about 0.2 should give good results), and rather broad opening (perhaps in the range of 40 to 300 pixels, depending on overall image size), let us brush in some color. Unlike in the first part of this series, when we were covering up small defects, now we will need to proceed with wide open strokes giving coverage to large areas at once, but with little density. For our first attempt, we will be using just three colors --a light blue, a darker green, and a reddish brick pink-- and not worrying about complete coverage of each part of the scene.** |
