Commons:图像指引

From Wikimedia Commons, the free media repository
Jump to navigation Jump to search
This page is a translated version of a page Commons:Image guidelines and the translation is 41% complete. Changes to the translation template, respectively the source language can be submitted through Commons:Image guidelines and have to be approved by a translation administrator.
Shortcuts
Creation on Commons

這些圖像指引是用在特色圖片候選優質圖片项目,用以選擇特色圖片優質圖片。至於最有價值圖片项目則是使用另一個準則。

  • 優質圖片評選應該要符合下列的要求,以及必需是由共享資源的用户所創建的。
  • 特色圖片候選應該要符合下列的要求,必需有一個「令人驚豔的因素」以及不論是否是由共享資源的用户所創建的。若是具有足夠多「令人驚豔的因素」和理由,特色圖片是允許在技術质量上未達目標。
  • 注意:一般來說最有价值图像候选並不像最有价值图像标准是以視覺上的质量來決定,由其特別的是它們在本質上具有歷史價值且無法再重現了。即使是它們有一些缺陷(例如顏色變樣、周邊暗角、灰塵等等),以精準的樣貌將它們呈現出他們原本被保存下來的模樣,這就是最好的做法了,只要它們保有適當的分辨率而保存了其中大部份的細節。

正常情況下,不應該會有多張特色圖片彼此之間很相似。特色圖片的排名的目的是為了辨別某個影像目前是否是最好裏面的其中一張,某個百分比之中很前面的一小部份。當整體的影像质量都提高的時候,有一些影像就從列表中去除。而優質圖片的排名的目的是為了辨別某個影像在它被創建的那個當下,共享資源的用户是否熟練地達到令人滿意的质量等級,這個辨別結果不會因後續有更新的進步而被消除。

一張圖像會向不同的人「敘說」不同的故事,並具有喚起他人情緒的角色,溫柔、發怒、慾望、厭惡、幸福、悲傷;好的攝影師不會被限制在只喚起令人愉快的感覺而已。 對於特色圖片來說,許多的投票者們都相信,一張技術平凡但主題非凡的圖片比一張技術非凡但主題平凡的圖片更有價值。其他的投票者們卻都同樣相信,每一張圖片都應該純粹地以它自身的特點來評判。例如,被技術上妥協的一張重要事件的照片,會因為它本身描述事件的重要性而得到一些支持,同時,也會有同樣多的反對者會因為它的技術质量原因而反對。

最重要的是,保持斯文。你正在評價的圖片是某個人的作品。避免使用一些字眼像是「看起來很糟」或是「我很討厭它」。若果你不認同,請三思而後行,並請說明原因。請記住,並不是每個人都有相同的英文掌握能力,請謹慎使用你的文字。

愉快地提名、愉快地評價、然後請記住...沒什麼是規則!

你的螢幕

在你評論別人的作品之前,建議你先校正你的螢幕。如果你沒做,你要牢記,你在太亮或是太暗的地方都可能無法看到細節。同時,一些螢幕可能對某個顏色調得過頭,以至於不在「中性」的顏色上。

查看下面的全黑底的圖片,你應該至少可以看到四個裏面其中的三個圓圈。如果你看到四個,那你的亮度就是被設定在高位,如果你看到三個,那很好,若是少於三個可識別,那亮度就是設定得太低了。

在一個可以gamma調整的螢幕上,當你從幾英呎遠看它,彩色圖片中的四個圓圈會被混入背景裏面。如果沒有,你可以調整gamma設定(從電腦裏面設定,不是從螢幕設定),一直到有混入。這或許「極其」難以達成,而且,有一點小小失誤也無傷大雅。未經校正的電腦螢幕通常會出現圓圈比背景暗的情形。

注意,在大多數的消費型液晶螢幕(桌機或平板)裏,視角會大大地影響看到的圖像--以一個靜止不動的頭的位置來看,正確地校正了螢幕的某個部份可能讓另一部份的螢幕變得不正確。點選一下這張圖以獲得更多的技術信息。

若是可能的話,建議使用螢幕校正器做校正。

另一件事也是很重要,你要確保你的網頁瀏覽器在顯示圖片時是在正確的分辨率。要確認這個,打開左邊的這個格子圖full 4000x2000 version。格子有8個方格的寬以及4個方格的高、其中每個方格都是邊長500個像素。在將它縮放到100%之後,你應該檢查它在現有的螢幕分辨率上,看起來是否合理。例如,如果你的螢幕是1920x1080,那在水平的寬度上,你應該調整到它只涵蓋4個方格,那就是2000個像素。由於捲動軸、選單等等因素,實際的可用的空間會略小於你螢幕的分辨率。

Firefox已知在Windows電腦上會有問題,在主控板裏的顯示設定已經被設定為不是100%的比例。對大型螢幕,常見的預設值是125%(中等),如此導致Firefox對所有東西都過度放大了25%,造成顯示出來的圖像與真正的比起來較不銳利!要解決這個問題,你可以改變這個比例值為100%,或是前往about:config(在網址中打入),然後改變layout.css.devPixelsPerPx1.0

圖像頁面的要求

  1. 要有版權的狀態。圖像必需是在符合某個合適的許可證的前提下才能上傳到共享資源。完整的授權要求放在共享资源:许可协议
    1. 聯邦議會(澳洲國會)駁回:僅僅是以「GFDL」或是以合併後的「GFDL與NC-only」去授權圖像做為授權的要求,這對再次使用來說,是不切實際的。並且,因此衍生一個結果:別拿出「我們最好的作品」。
  2. 圖像應該要:
    1. 符合共享資源的方針與指引,這包括共享資源:可辨識的人物照片
    2. 有一個有意義的檔案名稱,要適當地歸類以及在檔案頁面裏有一個一種或多種語言的精確描述。(可以參見共享資源:語言方針)
    3. 在表達上,立場中立
  3. 圖像內不要有廣告、簽名、或其他浮水印。每一張圖的版權或來源的資訊都應該放在圖像的描述頁裏面,並且不得與圖像的內容相抵觸。

優質圖片和特色圖片的圖檔

議題/
常見的問題
指引 討論 示例
圖像的尺寸
  • 圖像應至少要有2百萬真實畫素(動畫、视频、SVG可以除外),例如是1600×1250。對於「隨手可得」的圖像,若是圖像可以從分辨率得到好處,評論者就有可能會要求更多。這條規則不包括:由電腦透過免費授權的軟體所產生、或建構的圖像。
  • 圖像不應縮減畫素採樣(縮減尺寸)以便表現出較好的品質。縮減畫素採樣會降低儲存在圖檔內的資訊數量。一個縮減畫素採樣的人物圖像倒是很明智的,否則,經過很誇張的放大之後,所有身體的細節都會被看到(例如:皮膚、牙齒),這可以視為是冒犯或是違反個人權利。然而,對於特色圖片來說,未經縮減畫素採樣的原始版本是比較好的。
      放在共享資源內的圖像,有可能會被用在其他場合,不是只出現在電腦螢幕裏而已。它們也有可能會用用在印刷品上,或是出現在有非常高分辨率的電腦螢幕裏。

      我們無法預見未來會使用什麼樣的裝置,所以每個人的最佳照片的分辨率應儘可能地提高,是很重要的。

JPEG失真壓縮
  • 太高壓縮等級
  • JPEG品質在相機內的設定或是儲存時太低
  • 看得到JPEG不自然的樣貌
  • 圖像不要使用太高的壓縮。
      在你的影像相機或是軟體裏設定高畫質。例如,設定相機內的JPEG畫質為「最佳」,或者,若是你的相機是可以將圖像儲存為RAW檔案,你可以稍後透過適當的軟體轉檔變成可上傳的JPEG檔。在你將你已完成的副本存檔準備上傳時,所使用的JPEG壓縮的畫質是在80%到90%之間,這由讓你滿意的檔案大小來決定。

      在多次編輯的過程中儲存圖像,若是你需要在不同的編輯軟體之間開啟圖像,請使用編輯軟體的原生檔案格式,或使用一個標準不失真的檔案格式,例如TIFF或是PNG。重覆地編輯再儲存一個JPEG圖像將會逐漸地失去畫質。

      不要使用一個比原來軟體還大幅度高畫質的軟體,來儲存編輯後的JPEG,如此只會增加圖檔的大小而不會增加畫質。

视频
  • 顏色视频
  • 亮度视频
  • 可見的細粒
  • 刮痕、灰塵、髒污
  • 斑點
  • 圖像在以全尺寸觀看時,不應含有會讓人分散注意力的视频
      想要降低视频,使用可實施的最低感光度(例如:ISO 200底片的顆粒情形就比ISO 1600低!)。

      若照片是在很獨特的環境下拍攝,無法再度重現,圖像倒是可以透過軟體的過濾讓它變得更好。

      若是你無法找到到合適的程式或設備,你可以在Commons:Graphics village pump裏面提問。

曝光
  • 過度曝光
  • 爆炸性白光
  • 曝光不足
  • 陰影處缺少細節
  • 考量環境的影響,圖像應該正確地、適當地曝光。
       在正確曝光的圖像中,有意義的細節會被保留下來。

      有一點要注意,曝光時間也許可以達到一個擁有創意的效果,所以,這條指引應該要經由了解圖像概念或意圖的人評估過。曝光涉及快門與光圈的結合,以一條色調曲線去渲染出整張圖像,那條曲線理想地可以表達出圖像內令人滿意的陰影細節及明亮細節。這稱為曝光寬容度。圖像可以處在那條色調曲線的下側(較低範圍)、中側 (中間範圍)、或上側(較高範圍)。數位相機(或數位圖像)比傳統底片擁有較窄的曝光寬容度。

      缺少陰影細節並非必然是一個負面的特色。事實上,它可以是想要的效果的一部份。火熱的大面積精彩處反而是一個讓人分心的效果。在你使用數位相機拍照時,請檢視顏色直方圖。在你挑戰環境時,你可能被迫去運用重疊多張不同曝光時間的照片ー這稱為高動態範圍成像(HDR)編織

Color
  • Quality images must have reasonable colors and shouldn’t be too bright. Note that this does not necessarily mean natural colors.

Color balance can be often corrected by editing programs.

 When taking Photographs in a RAW image format, it is possible to adjust the white-balance in post-production, i.e. on the computer, without any loss in quality.

Focus and depth of field
  • Improper focus
  • Undefined focus
  • Insufficient depth of field
  • Too deep depth of field
  • Every important object on the picture should be sharp, considering the idea of the image.
  • The overall image should have clearly defined focus, for example, the main subject is in focus and the foreground and background are out of focus, or else, the whole scene is in focus.

 Depth of field is often low intentionally. If in doubt, ask.

 "Depth of field" (DOF) refers to the area in focus in front of and beyond main subject. Depth of field is chosen according to the specific needs of every picture.

 Large or small DOF can add to or detract from the quality of the image. Low depth of field can be used to bring attention to the main subject, separating it from the general environment. High depth of field can be used to emphasize space. At a given subject distance, short focal length lenses (wide angles) yield larger DOF than longer focal length lenses (telephotos). Narrow apertures (high f-numbers) yield larger DOF than wide apertures (low f-numbers).

Motion Blur
  • Too long exposure: image has become blurred because of hand shaking or subject moving too fast.
  • Motion blur should have a purpose, most often to emphasize motion.

 "Movement control" refers to the manner in which motion is represented in the image.

 Motion can be frozen or blurred. Neither is better over the other by itself – it's representation that matters. Movement is relative within the objects of the image. For example, photographing a race car that appears frozen in relation to the background does not give us a sense of speed or motion, so technique dictates to represent the car in a frozen manner but with a blurred background, thus creating a sense of motion. This is called "panning". On the other hand, representing a basketball player in a high jump frozen in relation to everything else, due to the "unnatural" nature of the pose may well be a good photograph.

Lighting
  • Distracting reflections (usual problem with built-in flash)
  • Inappropriate vignetting
  • Distracting harsh shadows
  • Lens flares
  • Lighting should be appropriate for portraying the subject.

 Light is said to be the most important ingredient of a photograph, and quality images are expected to have it right. The quality of a shot may depend on conditions beyond the photographer’s control, like weather at outdoor shots or stage light.

 Contrary to general belief, front lighting is not usually the best light as it flattens the subject. Side lighting often gives a better “texture” to surfaces. The best daylight is often early morning or late afternoon, or on a slightly cloudy day.

 When photographing in strong light, you may want to soften the shadows by using “fill flash”.

Editing
  • Unnecessary or inappropriate use of artistic filters and effects. Editing programs have wonderful artistic filters and scripts. Unnecessary use of these, however, can be detrimental to the image.
  • Digital manipulation for the purpose of correcting flaws in an image is generally acceptable, provided it is limited, well-done, and not intended to deceive. Typical acceptable manipulations include cropping, perspective correction, sharpening/blurring, colour/exposure correction, and removal of distracting background elements.
  • Extensive manipulations must be clearly described in the image text, for example by means of the {{Retouched picture}} template. Unmentioned or misrepresented manipulations, or manipulations which cause the main subject to be misrepresented are never acceptable.

A part of post-processing includes HDR and tonemappings. Some like using strong HDR effects for images shared online, but the possibilities of such techniques are often used in a way that means that images have little resemblance with reality. On the other side, some subjects such as church interiors often require further editing work and the combination of multiple images to avoid over- or underexposure. In such cases, extensive post-processing can even be desirable if done with appropriate care.

Composition
  • Unbalanced composition
  • Unclear subject
  • Non-existent subject
  • Too tight crop
  • Too busy
  • The arrangement of the elements within the image should support depiction of the subject, not distract from it.
    Foreground and background objects should not be distracting.

 The subject should not be cropped, unless it is only a specific part of the subject that is of interest. Foreground and background objects should not be distracting. Objects in front of the subject shouldn't hide important elements and background elements shouldn't spoil the composition (for example that the streetlight doesn't "stand" on someone's head).

 The Golden Ratio and Rule of Thirds are common guidelines for composition that have been inherited from painting. Centering the subject is often considered a negative practice. Subjects of interest are placed in one of the "interest points", where horizontal and vertical lines intersect (4 interest points are created). Horizons are almost never placed in the middle, for they "cut" the image in half. They are placed either in the upper or lower horizontal line. The main idea here is NOT to center the subject without a very good reason (such as symmetry).

Distortions
  • Tilt
  • Perspective distortion
  • Barrel distortion
  • Images should not be unintentionally tilted.
    Images of architecture should usually be rectilinear.
    Perspective distortion should either have a purpose or be insignificant.

 The human brain is a sensitive detector capable of spotting even a small tilt. Falling trees, towers and inclined water surfaces rarely improve landscape photography.

 Tilt can be easily corrected in almost any photo editing software. Various more complicated distortions can be adjusted in programs such as hugin and Panorama Tools. If you don't have access to suitable programs or don't understand them, ask at the Commons:Graphics village pump and someone may be able to process the image.

Stitched images, panoramas

  • Height
    • Guideline: Panoramic images need to have a minimum height of 800px.
  • Stitching
    • Common problems: Stitching artifacts. Colors or luminance are not consistent across the image. Horizon line sinusoidal or even more complicated shape.
    • Guideline: Getting a good panorama ready takes time. Recent releases of programs like hugin and Enblend make simple errors like bad alignment and ghosts at blurred seam lines less common than they used to be, but parallax errors and more intricate quality problems still occur. Two examples:
The ingredient photos were taken with a camera not in panorama mode, and camera-bundled software was used for the top stitch. One notices that the left part is darker, due to the camera exposing each photo individually. This could be dealt with by adjusting brightness before stitching.
More subtle errors are at the right of the castle, where there appear to be two vertical bands in the sky. Look where these bands touch the hill, at the middle one the stitching program misaligned, producing a ghost. Also, the program feathers the transitions. While this avoids a visible edge, one can see that in such feathering region, image noise is reduced, which makes these parts stand out from the rest of the image.
The bottom image shows that using different software, the photos can be stitched without such errors.
  • Lighting
    • Common problem: different exposure in different images, leading to overexposure or visible differences in brightness and posterisation.
    • Guideline: Even when photos are taken with the camera in panorama mode, unless one chooses an overall exposure for all images to handle the brightest part of the brightest image, then blown highlights are likely.
Ciemniak panorama.jpg
If possible, set for underexposure, as well as panorama mode. Expected advances in software based exposure correction may soon make panorama construction viable from a photo series not shot in panoramic mode. Until then, use the brightest part of your panoramic scene to set the in-camera exposure when shooting.
Some software provides blending algorithms that make the seamline invisible. But if the brightness of the original photos differs significantly, one still notices a transition in between photos. A few minor misalignments notwithstanding, this is what the top photo shows.
Some programs incorporate brightness adjustment for the photos, but the algorithm has to be designed carefully otherwise one can end up with posterisation effects like the purple and light blue patches in the clouds on the left in the bottom image.
  • Vignetting
    • Blending-only programs can do away with seam lines and smooth structure using feathered overblending, but to correct lens vignetting one needs a radius-dependent brightness correction.
Deliberately strong vignetting
The left image shows a technically acceptable stitch, except for the vignetting effect which has been strongly exaggerated. Good stitching programs incorporate vignetting correction. Make sure to incorporate good vignetting correction. Pre-processing the input images is less elegant, but one can obtain good results. In the sky can be seen three bright areas, separated by two darker bands. These correspond to the middles and the sides of the three original images. Although programs like Enblend remove visible seam lines, they do not remove vignetting effects. In the sequence hugin-enblend it is at the hugin stage where vignetting has to be corrected, either inside a recent hugin version or as already corrected input.
On the right is a more subtle example of vignetting, most visible in the sky, where one can see three bright areas from left to right separated by two darker bands. These correspond to the middle and the sides/corners of the three original images.
See in the photo below how the sky brightness spans the spectrum without being burnt out, but still the sky brightness has a wavy structure, most noticeable in the left part.
Tatra Mountains Panorama 01.jpg
  • Camera positioning
For the left stitch, the photographer captured the bottom part of the church, then stepped left and took a photo of the top part. The seam line is visible in the windows just below the clock, and one sees shifts in different directions in the middle and on the tower structures. Stitching software is not meant to cope with such parallax error as the problem here is located behind the camera, and the way out in this case was the availability of matching photos, albeit from a different perspective, to create the image on the right.
  • Image alignment
Proper alignment of images is a crucial first step and has been achieved in this view taken in the Western Scottish Highlands. But the exposure differs between images and cameras have vignetting, both make seamlines visible. And as these photos have been aligned regarding the distant features, some parallax errors can be seen at seamlines in the foreground. There exists software that makes such seams disappear and the parallax errors can be concealed by choosing a suitable seamline.
  • Composition
    • Common problems: Panoramas frequently lack a central focal point. If taken within urban settings, much of the scene may be uninteresting with unattractive features such as rubbish bins and light poles almost impossible to avoid.

Color space

Different color spaces cover different colors and yield different rendering.

Different color spaces exist, which determine how the colors in an image are stored and displayed. sRGB is most common and compatible, while other color spaces, notably Adobe RGB, allow more colors but are less compatible, and must be correctly supported by users' computers.

Simplest is to use sRGB, which is usually default on Windows and Linux, but must be selected when saving files on Mac (prior to OS X 10.6). For further options, read on.

Please see “sRGB Correct ColorSpace Tutorial for the Internet” by Gary Ballard for illustration of problems of mismatched color spaces.

Guidelines

Images should either be in sRGB (either untagged, or specifically tagged as sRGB), or, if in another color space, explicitly tagged as such. Tagging means either including an Exif tag with the name of the color space (options are "sRGB", "Adobe RGB", and "other"), or including an ICC profile, which explicitly specifies the color space. Including an embedded profile is safer, as Exif tags are not always respected by web browsers. Untagged non-sRGB images ("mystery meat") will not render correctly on the vast majority of computers.

For most Windows and Linux users, sRGB is default unless changed, and untagged images will generally be sRGB. However, Mac users should take care that their images are exported in sRGB, and not "Generic RGB" or "Apple RGB".

Best color spaces are sRGB or, optionally, Adobe RGB, which is wider, as these are standard color spaces and hence easiest to support and for other editors to use. If using a non-sRGB color space – say for greater color range – consider making an sRGB version of the image for greater compatibility.

Technical details

It is safest to use sRGB: which is the default on most computers, including Windows and Mac OS X 10.6 and later. Images in other color spaces will not render correctly at all in many web browsers; color profile support is included and enabled by default in Safari, and in Firefox 3.5, but not in all browsers.

Untagged non-sRGB images will not render correctly except by chance. Notably, untagged Mac images prior to OS X 10.6 used a different color space (Apple RGB prior to OS X, "Generic RGB" in OS X prior to 10.6), which notably included a gamma of 1.8, rather than 2.2; these images thus appearing dark when viewed on non-Mac computer that assumes sRGB (with gamma of 2.2).

Location

It is recommended to geocode images by using {{Location}} and/or {{Object location}} templates.

If the location is difficult to obtain (eg. in the wilderness areas), you may have the choice of giving the general location (to 3 decimal places or fewer, as appropriate), use {{Location estimated}} or simply mentioning a nearby geographical feature (eg. valley, river, mountain range) or a settlement that would help to identify the location.

Photos that can't or shouldn't be geocoded include those which would show the locations of endangered plants and animals, military installations, studio photos or locations that should be hidden to respect rights of privacy. To communicate this in the image, you may wish to use {{Location withheld}} template.

Exif

See Commons:Exif for help on using and editing Exif metadata.