PPI is an abbreviation for "pixels per inch" and it belongs to the image category of digitization. PPI is sometimes used interchangeably to the slightly different concept of DPI, which refers to "dots per inch" and might have a distinct meaning in certain situations. But they are often referred to as the same basic concept. PPI is usually used to characterize the capabilities of an imaging device or a digital image when it comes to the resolution. Basically, it describes the proficiency of a device such as a scanner to render the smallest units of information in the structure of an image.  

The white point of a monitor refers to the color of the brightest white it can generate. If uncorrected, most computer monitors have a white point that is somewhat blue compared to normal daylight or artificial illumination. To achieve an accurate match between images on a monitor and prints, the color temperature of the monitor must be matched to that of the illumination used to view the prints.

How to adjust white point in Photoshop:

The Auto option for Levels and Curves and the Auto Tone command automatically adjust the black point and white point in an image. This clips a portion of the shadows and highlights in each channel and maps the lightest and darkest pixels in each color channel to pure white (level 255) and pure black (level 0). The intermediate pixel values are redistributed proportionately. As a result, using the Auto option or Auto Tone increases the contrast in an image because the pixel values are expanded. Because the Auto option and Auto Tone adjust each color channel individually, it may remove color or introduce color casts.

The Auto option and Auto Tone give good results in certain images with an average distribution of pixel values that need a simple increase in contrast.

By default, the Auto option and the Auto Tone command clip the white and black pixels by 0.1%—that is, it ignores the first 0.1% of either extreme when identifying the lightest and darkest pixels in the image.

How White Point in Photos Works:

While you can auto adjust the white point, in many cameras you can slide the temperature slider and when you like the results you take the picture.

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The HSL color space categorizes colors by their hue, saturation, and lightness. As in the HSV color space, Hue corresponds tothe colors around the outside of the color wheel and Saturation refers to the intensity of a color.Varying hue with 100% saturation and 50% lightness. Varying saturation with 0% hue and 50% lightness

The HSL color model allows the color to range from a color that is fully saturated to gray. The HSV goes all the way down to a white, which is not useful to many users of the color model. On the other hand, light can range from white to black in a HSL model (with the desired color in between), while the similar HSV color model can only range from the desired color to black. It is obvious that the HSL color model does indeed offer more freedom

The Hue slider will acually change the color whether its one color that you've targeted or all colors in the Master channel. Use it in conjunction with the colorize check box (bottom right) to achieve almost limitless monochromatic effects, or use it on a targeted color to alter the color temperature. For example, say you have some greenery (perhaps some ivy in the background?) that you want to make more aqua rather than warm and yellow. Make sure you're editing the greens and slide the hue slider to the right slightly. Keep in mind that this will effect all the greens in the image.

Now for the bars at the bottom of the dialog. The color bars at the bottom show your color before (the top color bar) and your color after (the bottom bar). The color inside the middle bracket (which shows up when you are targeting a specific color) is the main color that you will be affecting and the colors inside the outer brackets are used to feather your selection. You can resize any of the brackets to fine tune your selection and narrow down the color that you want to affect.

An anaglyph is a pair of black and white stereo images prepared for viewing with special glasses that have a red filter for one eye and a cyanfilter for the other eye. One image is printed in red and can be seenonly by the eye with the red filter; the other image is printed in cyan and can be seen only by the eye with the cyan filter.

Color depth (also known as bit depth) refers to the number of bits used for the color of a pixel or used for every color component of a pixel. Low color depth stores a value which represents the index into a palette whose colors are fixed by the hardware. There also are pseudocolor palettes which are changeable. When the number of bits rises, the color value can encode relative variations of brightness of red, green and blue to refer to a color in the RGB model. Color systems such as 8-bit color, high color (15/16-bit) and 18-bit are pretty limited, while true color (24-bit) or deep color (30/36/48-bit) can provide millions or billions of colors. All TV and computer displays form images based on red, green and blue.

Additive color mixing is the process of combining light of two different colors. For example, adding red and green light makes yellow

A pixel is the smallest element of a picture on the screen. Its etymology comes from the word picture ("pix") and element (-el). It's the smallest component of any digital image. A picture resembles the original according to the number of pixels used to represent it. This number is often referred to as the resolution. Pixels are usually organized in a regular two-dimensional grid, which allows most operations to be implemented to each pixel. The number of bits per pixel (bpp) reflects the colors that can be represented by the pixel. Some systems can also feature subpixels or megapixels.