The preliminary application of histogram

The preliminary application of histogram

Like orthopaedic surgeons need to accurate X-ray diagnosis of the injury, canvas prints nz photographer has tools to eliminate the interference of camera, display and environmental objective interpretation of the picture of the brightness distribution. The "photographer X-ray" is the histogram. Histogram has two roles in photography, one is we optimize the previous guidance to record the original information, 2 it is in the later to help us to balance the brightness of the photo regional distribution. This paper will mainly talk about how to reference histogram, taken in the early stage of the exposure of a reasonable, and can be up to the best record the raw file of the original information.

What is histogram? canvas prints online When we remove the color information of photo and the rest of the black-and-white images only recorded the brightness distribution of environment at that time. Images of brightness is decided by two factors, one is the brightness of the original object, such as the snow is very bright sunlight, there would be dark and black velvet pulled, 2 it is decided by our camera exposure and effect of different parameters can obtain different exposure. People put the brightness of the image is divided into 0 to 255 a total of 256 values, among them the most dark area 0 (black, 255, said the most bright pure white, and the brightness of the gray in the middle of the figure is different.

If we further divide the brightness into five areas. Among which exposure (adjustable) is the middle of the picture brightness area, the area in the picture is very rich and delicate, a lot of details are under the moderate intensity. The shadows and highlights the corresponding pictures on both sides of the darker and lighter areas, although they didn't detail the exposure area so delicate, but still store a lot of information. We often say that increase shadow, reduce the secular photograph can recover the details, is refers to the two parts of the brightness to the middle of the exposure area, so that became more delicate and transition, and levels. The black is the darkest areas of the photo, white is in the picture the brightest area, basic not any details in these regions, but black and white areas made the comparison and contrast between the pixels to the photos. When we use the horizontal axis represents the brightness of the 0-255 numerical, vertical axis represents in the picture corresponding to the number of pixel brightness, this function is called image luminance histogram. The general digital camera, can screen shot of the preview window before shooting, or take pictures of the after the completion of the browser window, set the histogram view options, you can refer to the instruction set of the camera.

In the early period of the histogram in photography there are three references:

1. Find the image in the photo and owe exposure area

When we take photos, the camera is exposed through the shutter, the actual brightness of the field environment mapped to the 255 to 0 of the photo record on the range. A piece of the ideal exposure should be below, histogram like normal distribution curve, there were very few records in white and black part, some pixels in the shadow and highlight areas of the distribution but more pixels or in the middle of the histogram in the middle of the range. Once we exposure parameter is set wrong, photos will owe exposure or whiteout, manifests in the histogram is a side there is a lot of blank, on the other side is overflow by histogram of pixel edge cut off. A photo of serious image histogram will be like the image below, histogram right be cut off directly, 255 pure brightness values that contain a huge number of pixels. This means that the red circle in the sky brightness is very high, because of the camera tolerance, only pure white in the form of a record in the photo, all details are lost. The dark parts of the photo is not how many pixels at the same time, we did not fully use of photos record information space. This time will need to be by reducing exposure compensation, narrow aperture, lower ISO, speed up the way of the shutter speed to reduce exposure.

The preliminary application of histogram (1)

2. Prompt environment brightness contrast is more than the tolerance of the camera

If white and black areas histogram is not blank, and both the image and less exposure to the above said, means that the environment of the brightness difference is too big, the camera has been difficult to record all information. Histogram reminds us that at this time, you need to use the gradient ash filter or late surrounded by exposure to synthetic method, to balance than the light.

3. Help us to the right exposure

The camera can produce noise at the same time record information. In the region of the lighter, as recorded by the light more, so the noise is not obvious. In the darker area, the camera records little light signal, noise will be highlighted. Especially if late again to the darker carry bright, noise will be more obvious. This situation is what we call "SNR" (receive light signals and chip itself in the number of noise ratio) is too low. In order to improve the signal-to-noise ratio of photos, 2003, photographer Michael Reichmann puts forward the concept of "exposure" to the right. In the photo light without overflow, let the pixels in the photo records in brighter area as far as possible. Histogram is right, as far as possible let white area there is always some pixels.

Because the camera display effect is limited, acrylic prints and the human eye is sensitive to light of the special. General exposure photo look directly to the right is the image, it is difficult to and 1 mentioned in difficult apart from the serious image to save. At this time only a histogram can help us to accurately grasp the exposure information, as long as the histogram is the most the right side of the position of pure white no accumulated a large number of pixels, photo is "exposure" to the right, not difficult to retrieve the details of the serious image.

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