Okay, I admit it. The title to this blog sounds pretty boring. However, this is pretty important stuff. Apart from getting a compelling composition in camera, controlling tonal contrast during post-processing is perhaps the most important part of creating a successful image. So, read on!
First, what does tonal contrast mean from a photography perspective? It is simply the magnitude of the difference between the light and dark areas of the image. To see this visually, let’s look at the histogram… a tool found in your post-processing software that can help you control contrast more effectively. In Adobe Lightroom, you can make the histogram visible by making sure the word Histogram is checked under the Window menu. Whatever software you use, it should have the option to view a histogram.
Identical tones in your image are reflected in the vertical movement of the graph, while differences in tones are reflected in the left to right movement. An overall darker image results in a histogram concentrated on the left, while a lighter image results in concentration on the right. The following should make this clear…
The image below is just a gray box. Every pixel is filled with the same tone… middle gray, which is exactly halfway between pure black and pure white. This zero contrast image results in a histogram that is made up of a single column right in the middle.
Now, look at the next image. As expected, the histogram has two columns at the edges… the left representing the black pixels and the right representing the white pixels. All of the pixels are concentrated in two tones.
Lastly, here is an image with a gradient applied from pure black to pure white. You can see what the histogram looks like in this case, with a full range of tones.
So, how do I actually control contrast and how do I use the histogram when processing an image? Although I work with contrast at different stages in post-processing, I initially adjust contrast as one of the first steps, right after white balance and exposure if needed. I will focus here on this initial contrast adjustment using a landscape image as an example.
The image below is a pretty extreme example of one that completely lacks contrast and looks “gray” in tone. The histogram is concentrated around the middle. This image can be substantially improved by increasing contrast.
Below is the same image after a quick contrast adjustment. This image is not finished with processing, but it certainly looks a lot better already. The histogram shows greater left to right movement. Each side of the graph does not quite reach the edge. I do this because I like to leave myself some room for a later contrast adjustment in Photoshop.
In the partial screenshot above, you can see the adjustments I made using the sliders in Lightroom. Other software should have similar sliders. Again, this is a pretty extreme example, so my adjustments are pretty extreme here. There is no real right way to do this, but here is what I did for this image:
First, looking at the histogram, I moved the Blacks slider to the left to get the leftmost part of the graph line fairly close to the edge, but not touching. So, there is no pure black in this image. If this image had pure black from the start, I may have moved the slider to the right to reduce the pure black in the image.
Next, I looked at the darker parts of the image (ignoring the histogram) and adjusted the Shadows slider so that the image had greater contrast, but without losing detail in shadow areas. You usually want to still be able to see detail in at least some of the shadows.
Third, looking at the histogram, I moved the whites slider to the right until the graph line was close to the edge, but had room to spare. If the image didn’t look good with that adjustment, I could have simply backed off on the adjustment. Also, if the graph was up against the right side at the beginning and I didn’t want pure white in the image, I would have moved it left to reduce or eliminate the pure white cells.
Fourth, looking at the image, I adjusted the highlights slider until the image looked good and the lighter areas of the image showed some nice contrast.
Fifth, I went back and tweaked the sliders again.
It is important to note that this is really only an example of how I initially adjusted contrast for one particular image. In many cases, you want to reduce contrast, rather than increase contrast. For some images, it is okay or desirable to have a fair amount of pure black and/or pure white in the image. In some cases, you want your image histogram concentrated to the left, middle or right. An image of a night sky will likely have a histogram that shows a lot of dark tones and pure black.
So, the above doesn’t apply in all cases. But, hopefully this exercise is helpful to you. Most importantly, be sure to balance what you see in the histogram with what looks good to your eyes.
Sawa, ninakubali. Kichwa cha blogi hii kinasikika kuwa chenye kuchosha sana. Hata hivyo, hii ni mambo muhimu sana. Mbali na kupata muundo wa kuvutia katika kamera, kudhibiti tofauti ya rangi wakati wa baada ya usindikaji labda ni sehemu muhimu zaidi ya kuunda picha ya mafanikio. Kwa hiyo, endelea kusoma! Kwanza, tofauti ya rangi inamaanisha nini kutoka kwa mtazamo wa upigaji picha? Ni ukubwa tu wa tofauti kati ya maeneo ya mwanga na giza ya picha. Kuona hii visually, hebu kuangalia histogram... chombo kupatikana katika programu yako baada ya usindikaji ambayo inaweza kukusaidia kudhibiti tofauti kwa ufanisi zaidi. Katika Adobe Lightroom, unaweza kufanya histogram kuonekana kwa kuhakikisha neno Histogram ni kuangalia chini ya menu Window. Chochote programu unayotumia, inapaswa kuwa na chaguo la kuona histogram. Sauti sawa katika picha yako huonyeshwa katika mwendo wa wima wa grafu, wakati tofauti katika sauti huonyeshwa katika mwendo wa kushoto kwenda kulia. Picha nyeusi kwa ujumla husababisha histogram iliyojikita upande wa kushoto, wakati picha nyepesi husababisha mkusanyiko upande wa kulia. Yafuatayo inapaswa kufanya hili wazi... Picha hapa chini ni sanduku tu kijivu. Kila pixel imejaa sauti ileile... kijivu cha kati, ambacho ni sawa na nusu kati ya nyeusi safi na nyeupe safi. Picha hii ya tofauti ya sifuri husababisha histogram ambayo imejumuisha safu moja tu katikati. Sasa, angalia picha inayofuata. Kama inatarajiwa, histogram ina nguzo mbili kwenye kingo... kushoto kuwakilisha pixels nyeusi na kulia kuwakilisha pixels nyeupe. Pikseli zote zimekusanywa katika sauti mbili. Mwishowe, hapa ni picha na gradient kutumika kutoka nyeusi safi kwa nyeupe safi. Unaweza kuona jinsi histogram inaonekana katika kesi hii, na mbalimbali kamili ya sauti. Hivyo, jinsi gani mimi kweli kudhibiti tofauti na jinsi gani mimi kutumia histogram wakati wa usindikaji wa picha? Ingawa mimi kufanya kazi na tofauti katika hatua tofauti katika baada ya usindikaji, mimi awali kurekebisha tofauti kama moja ya hatua ya kwanza, moja kwa moja baada ya usawa nyeupe na mfiduo kama inahitajika. Mimi itabidi kuzingatia hapa juu ya marekebisho haya ya awali tofauti kwa kutumia picha ya mandhari kama mfano. Picha hapa chini ni mfano pretty kali ya moja ambayo kabisa haina tofauti na inaonekana <unk>gray<unk> katika sauti. Histogram ni umakini karibu katikati. Picha hii inaweza kuboreshwa kwa kiasi kikubwa kwa kuongeza tofauti. Chini ni picha hiyo hiyo baada ya marekebisho ya haraka ya tofauti. Picha hii haijakamilika na usindikaji, lakini hakika inaonekana bora zaidi tayari. Histogram inaonyesha harakati kubwa kutoka kushoto kwenda kulia. Kila upande wa grafu haufiki kabisa ukingo. Mimi kufanya hivyo kwa sababu mimi kama kuondoka mwenyewe baadhi ya nafasi kwa ajili ya baadaye tofauti marekebisho katika Photoshop. Katika sehemu ya screenshot juu, unaweza kuona marekebisho mimi alifanya kwa kutumia sliders katika Lightroom. Programu nyingine inapaswa kuwa na sliders sawa. Tena, hii ni mfano pretty kali, hivyo marekebisho yangu ni pretty kali hapa. Hakuna njia sahihi ya kufanya hivyo, lakini hapa ni nini mimi alifanya kwa ajili ya picha hii: Kwanza, kuangalia histogram, mimi wakiongozwa weusi slider kushoto kupata sehemu ya kushoto ya mstari grafu pretty karibu na makali, lakini si kugusa. Kwa hiyo, hakuna rangi nyeusi safi katika picha hii. Kama picha hii alikuwa safi nyeusi kutoka mwanzo, naweza kuwa wakiongozwa slider kulia kupunguza nyeusi safi katika picha. Ifuatayo, niliangalia sehemu nyeusi za picha (kupuuza histogram) na kurekebisha slider ya Kivuli ili picha iwe na tofauti kubwa, lakini bila kupoteza maelezo katika maeneo ya kivuli. Kwa kawaida unataka bado kuwa na uwezo wa kuona maelezo katika angalau baadhi ya vivuli. Tatu, kuangalia histogram, mimi wakiongozwa nyeupe slider kulia mpaka mstari grafu ilikuwa karibu na ukingo, lakini alikuwa na nafasi ya ziada. Kama picha haikuonekana nzuri na marekebisho hayo, ningeweza tu kurudi nyuma juu ya marekebisho. Pia, kama grafu ilikuwa juu dhidi ya upande wa kulia katika mwanzo na sikutaka nyeupe safi katika picha, Ningependa kuwa wakiongozwa kushoto kupunguza au kuondoa seli nyeupe safi. Kwa mfano, kwa kuangalia picha, nilibadilisha slider ya highlights hadi picha ilionekana nzuri na maeneo nyepesi ya picha yalionyesha tofauti nzuri. Tano, nilirudi na kurekebisha sliders tena. Ni muhimu kutambua kwamba hii ni kweli tu mfano wa jinsi mimi awali kurekebishwa tofauti kwa ajili ya picha moja maalum. Katika visa vingi, unataka kupunguza tofauti, badala ya kuongeza tofauti. Kwa baadhi ya picha, ni sawa au ya kutamaniwa kuwa na kiasi cha haki ya nyeusi safi na / au nyeupe safi katika picha. Katika baadhi ya kesi, unataka picha yako histogram umakini kwa kushoto, katikati au kulia. Picha ya anga la usiku yaelekea itakuwa na histogram inayoonyesha rangi nyingi za giza na nyeusi safi. Kwa hiyo, mambo yaliyotajwa hapo juu hayatumiki katika visa vyote. Lakini, natumaini zoezi hili ni muhimu kwako. Kwa hiyo, ni muhimu sana kuzingatia kwamba histogram inaonyesha kile ambacho inaonekana kuwa muhimu kwa macho yako.