Module 5. Digital Image Treatment


Evaluation Criteria:

Perform digital image processing, assessing color, format and contrast characteristics and using still image generation, processing and retouching techniques.

Evaluative learning standards:

1.1. Being able to correct anomalies of the fixed image originals, and makes the necessary adjustments of contrast, gray balance, brightness and saturation, adapting the result to the characteristics of the medium or final support of the images.

1.2. Being able to adapt and adjust the images to the technical characteristics of the medium or final support, guaranteeing, where appropriate, the space-time register and the continuity of the sequences of still images necessary for the elaboration of the visual material.

1.3. Being able to elaborate the final image of the project through the application of geometric transformations and necessary perspective effects, using specific editing techniques and tools.


Color spaces.

Imagine for a moment that you are a painter and some clients ask you to paint a wall of a certain color. You wear the pantone and choose what color suits your tastes. But you warn them; It is not the same what you see in those sheets with scales of colors that what will then be seen on the wall. The customers feel bewildered. The same happens to the photographer when he has to see his image on paper or on a screen. Take the picture and then want to edit it with a program on the computer screen. You already realize that they are not the same colors. And the same happens when you print the image on photographic paper. Neither are the same colors that he had on the monitor, so they are not the ones he captured either. More or less are the same color ranges, but they are not exactly the same. To control all this mess, there are the color spaces. If you have had the possibility of seeing a visible spectrum, you will have seen that the colors are ordered from red to blue according to their vibration, according to the number of cycles per second and, therefore, to a certain vibration, we will always have the same color. When a device wants to interpret that particular vibration (that strip of light) to a certain color, it can give a more or less reliable interpretation. The systems of ordering these colors employ three data, as a triangle (X, Y and Z axes) within an RGB model (monitors) or a CMYK model (printers). As you see, there are two systems. And the worst is that within the RGB there are many other models (such as Photoshop, or the sRGB of HP and Microsoft). There are conversion systems, reliable, but not exact. In both cases we have mixtures of additive colors (superposition leads to white) or subtractive (superposition leads to black) and each system can use one or the other, so the complexity and impossibility of a standard model is undeniable.

Gamma, encoding-decoding of luminance or color values.

The Gamma refers to a type of correction that is made to adjust the digital part of the imaging to be as close as possible to the perception of the human eye. You will have noticed. You make a picture of a poorly lit scene and you realize that you saw something, but the camera sensor did not notice anything. And in other cases you will have seen that there are things that dazzled you and that were clear when you photographed them. In order for the image capture to be adjusted to the vision, the machine has to make gamma corrections or contrast selection. In addition, we will have coding systems from the analog signal (the image itself) to the digital output and the backward one with the decoding (to have the original image on a screen or a paper). The collection of codecs is huge and it is necessary to have them updated to work with them.

Regarding the colors, these values ​​are made with the luminance, which we have already studied.

Correction of color dominants.

When we work with professional photography, rarely the correction of targets will play tricks on us, but in JPG we can find that the camera has "corrected" the color and we have colors that dominate others, unreally coloring the image . In these cases we have to correct the dominance of color, distributing the colors evenly. This will be done from an image editing program. An extra layer is made in which we correct the colors and we superimpose the two layers to have a correct version of the image.

Mode and depth of color, resolution, dimensions and format.

A color mode is a coordinate system that allows us to define the color of each point of the image. The common ones are the RGB and the CMYK, although we can also find the gray scale for black and white images. These coordinates, these data will depend on the color depth. If, for example, we had 1 bit of color depth, the possibilities would be two: white (1) or black (0). With 8 bits we have 256 colors and with 24 bits we have at our disposal 16,700,000 colors. The resolution of the image is the number of pixels per inch that we have in an image. On a monitor there is a different number than on high quality photo paper, which is also different from what we have on an HD screen, so we have another problem when it comes to being clear about what the viewer will see. The unit is usually the Megapixel which are millions of pixels per unit. The dimensions and format we saw before, both in 4: 3 or 16: 9 and with the photo, video and audio formats (jpg, mp4 and mp3, for example).

Depth of color.

We have seen it in the previous section. Just remember that currently we work in 24 bits, so the weight of the images is considerable and the range exceeds 16 million colors. We will also remember that it is related to both the color mode and the color spaces and their lack of standard (RGB and CMYK are common, not forgetting the HBS for Gimp).

Resolution (pixels), color depth (bits) and file size.

With what we have seen in this block we can already understand the relationship between the mapping of the pixels (resolution) the weight of the colors in bits (color depth) and the size of the file. The more information we dedicate to resolution and color depth, the larger the file size will be. In some cases we must sacrifice the amount of information we want to store (even be very hard workers and think what data is redundant and we will not need it) so that the weight in the memory of the camera or computer is as small as possible. A common solution is to use JPEGs, but it will not always be the right solution for a professional photographer.

Separation and mixing of channels.

By channels or layers we understand that there are different superimposed images, especially with the same image but different colors. Before teachers used a thing called transparencies that were fantastic and that we superimposed to make more complex the image we wanted to explain. The same was done with the robot portraits of the police. You added to the projector a transparent layer of the shape of the head, another of the eyes, another of the nose, etc. Until you had the face of the suspect. Well, photography happens the same. To begin with, when printing on photo paper, the colors go separately. If you have had the opportunity to reveal in a laboratory or to see a photographic printer, you will have seen that from a contrasting image in black and white to another one with reds, yellows and blues. And in the end you do not have a weird thing, but a fairly trustworthy version of the taken picture. In editing programs such as Photoshop and Gimp, we can take the original photo (the file, let's go) and convert it into several images separated by color channels. So we can edit each one separately, without affecting others, but changing the final result. The trick is that they are in gray scale, but with a certain range of RGB (or CMYK), so we see yellow, red or blue. And then we mix it.

Grayscale, true color and indexed color modes.

Continuing with what was seen in the previous section, we see that the gray scale determines the layers. Therefore the color we use will be mainly the one that comes indexed (8 bits to 256 colors), by RGB (usually by 16 million colors at 24 bits), in gray scale (also 256 colors, surprising right? ). But we can also choose, with greater weight, to use true color (even more so than RGB), although it is not advisable to give so much weight to something that is going to be redundant. By the way, we have left the CMYK process and the two colors of the bitmap. All of them are used. In multichannel mode, we can use a different format for grayscale and color for each layer or channel. The result, if done well, will come up with a fantastic final mix.

Overexposure and underexposure adjustments.

Another thing we saw in the previous block. In a very short shutter opening we will have an underexposure in the light of the image and in openings of several seconds we will have an overexposure. For each case we will need to think about what result we want. A nocturnal photo will hardly work with underexposure, while the overexposure will "burn" the image with very warm colors. If that is what we want, go ahead, but in all cases the underexposed rule to capture fair light and frozen motion and overexposure for situations with low light and / or no movement.

Contrast adjustments, gray balance, brightness, tones and saturation.

Remember that in a histogram we can adjust ranges by levels and within these levels we can find contrasts, brightness and saturation. Let's see one by one. The contrast separates the tones of greater color (within gray scale would be the dark ones) from the lighter ones or from the whites. It serves to highlight highlighting the richest part of color of the rest. The balance of gray is related to color dominance and refers to how the black and white elements work within a color photo. If we only had grays, we would control this aspect without problems, but we have to do it mixing cyan, magenta and yellow. For light tones, we will almost have none of these colors and for dark colors, all will be above 90%. The brightness highlights the luminosity. When more brightness, whiter will be the image and less contrast we will have and with zero brightness, we will almost remain in black. The tone setting selects a certain color and focuses on making it more or less present, while saturation (such as heat or "warmth") causes colors to be highlighted or corrected towards neutral tones.

Creation of images by computer and other devices with possibilities of transmission of reproduction of images and sounds.

The CGI or computer generated image is relatively recent in photography and animation. We work on special effects and digital painting. We use the term infographics for this type of images. You already know the results, from the images created by editors like Photoshop or Gimp in which you start from scratch or from an original image that is modified to unsuspected limits, to 3D animations that are used both for animation (Pixar type) or effects specials (type ILM). With respect to sound, we have synthesis (musical creation) and digital sound effects (all in the style of Skywalker sound).

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