Articles and Information
by Members for Members

Possible topic for April_04

The human eye perceives color in what is known as the HSB scheme: Hue , Saturation, Brightness. A PC monitor emits light when an electron beam hits a pixel. Pixel is an acronym for picture element and consists of a triad of red, green, and blue phosphor dots on the inside face of the screen. The inkjet printed image reflects light from dots printed with ink in the CYMK system: Cyan, Yellow, Magenta, and Black. A pure printed color is obtained when all but one frequency of light is absorbed. It is no trivial task to match the colors among the systems.

That said, the basis of understanding photo editing software is to understand digital color, including the two non-colors: black and white. A BLACK PIXEL on the monitor is one that has not been energized by the three-beam electron stream; it is OFF. A BLACK DOT in the image on a printed page is just that- a dot of black ink OR a mix of CYM inks (which gives a muddy black). A WHITE PIXEL is a phosphor triad that has been energized at full intensity by all three electron beams. A WHITE DOT in the paper image is the absence of all inks.

When we talk about digital we mean a finite number of steps within a range as opposed to analog's smooth ramp of values. Think of a multi-level light switch compared to a smooth operating dimmer. At a color resolution of 24 bits, 8 bits are assigned to each basic color in the RGB and CYMK system. This allows for 256 steps (2 7 to 2 0 ) of value for each color. By combining the levels of phosphor illuminations (256 x 256 x 256), you get almost 17 million colors to play with.

ASIDE: The binary system used by the computer uses only two states – a 1 (one) or a 0 (zero). The mathematics is “base 2;” our decimal system is base 10, utilizing our ten fingers (digits). To convert a binary number to decimal, use powers of 2. The range of numbers is determined by the number of bits, thus for eight bits (8 bits = 1 Byte) we have:

2 7   2 6   2 5   2 4   2 3   2 2   2 1   2 0

128   64   32   16   8   4   2   1

Binary 101 means 4 + (no 2) + 1 = 5 10 , 11111111 2 = 256 10 , the sum of 128, 64…

Software photo editors rely on distinct values of pixels to accomplish their tasks. The ability of a lasso tool or magic wand to select an object relies on the difference in color value of neighboring pixels. A gal standing in front of a green wall wearing a red shirt and a blue skirt may not be all that fashion conscious, but it makes it fairly easy for a photo editing program to pick out the red shirt. Selecting her shadow in the shadow of the wall would be much more difficult for the tool.

A major concern in today's world is time and space, especially when it comes to communication. Taking the time to study a print hanging in a museum and downloading a photo over a broadband connection approach two extremes in digital photography. The file format used to e-mail pictures has a major bearing on the content and file size. Another aspect is the World Wide Web with its many browsers, OS's (Windows, MAC, Linux, etc.), and broadband or dial-up connection speeds. I'll try to give a brief description of some popular file types and their suitability to different purposes.

Before we consider formats, let's take a look at some popular compression schemes; there are two basic types: lossless (all information retained) and lossy (sacrifice data for compactness).

RLE Run Length Encoded – instead of repeating pixel information, pixels with the same values are grouped and their number (population) is coded. This is a lossless scheme.

LZW Lemple-Zif-Welch (the three inventors) – lossless, best for pictures with large areas of single colors such as simple Paint Bitmaps.

JPEG Joint Photographic Expert Group – a lossy compression scheme that can be extreme. Repeatedly resaving a .jpg file will reduce the data significantly. Try to go back to the original for editing and then save as a new JPEG file.

CCITT from the French International Telegraphed and Telekeyed Consultive Committee – a lossless scheme for black and white images like clip art or line art.

ZIP (not an acronym) – like LZW, it is most effective with large areas of single color.

FILE FORMATS:

BMP Bitmap – a raster format meaning pixels are specified as to position and color. RLE compression can be employed. Files can be very large and are not scalable.

GIF Graphics Interchange Format – raster format with LZW compression (lossless) but is restricted to 256 colors. Good for the Web and HTML e-mail. Late development allows for animated GIF images. Web Safe GIFs are restricted to 216 colors.

JPEG filetype extension is shortened to .jpg – lossy compression is cumulative. It is the most popular format for Web and Email. 24 bit JPEG files retain a lot of color info. With a sacrifice of quality, files can be very small.

PNG Portable Network Graphics – developed as an alternative to GIF, copyrighted by Compuserve, it supports 24 bit images and transparency in grayscale and RGB images. It has lossless compression.

TIFF Tagged Image File Format (.tif) – non-propriety, uncompressed raster format with the richest data. Files tend to be very large but are the excellent for editing.

There are other formats, but this article is meant to be short and by no means exhaustive.

There is an ongoing debate about monitors and photo editing that pits CRTs (Cathode Ray Tubes) vs. LCDs (Liquid Crystal Displays). At the present time, CRTs beat out LCDs for graphics and animation - but not by much. Aging affects both devices. The vacuum inside a CRT is far from perfect and phosphors change with age, loosing some of their capacity to fluoresce with their initial brightness. LCDs start out much brighter and are superior for text. However, the backlight is a fluorescent source and also has aging problems. On the horizon is LED (Light Emitting Diode) backlights, which will be a considerable improvement but probably quite expensive

For the digital photographer, high end displays (both CRTs and LCDs), benefit by color calibration. Out-of-the-box displays are rarely optimized for color rendition. In the past, equipment to achieve near perfect color matching was beyond the pocketbook of amateurs. In the past year, affordable (a reviewer's opinion) $200 - $300 kits have become available for both CRTs and LCDs. They come with USB connected colorimeters and software that puts up various color screens for calibration. PC World magazine recommended X-Rite's MonacoOptix XR, at $299, a Best Buy.

{Try an experiment – demo Neutral_Gray.psd on laptop and TV monitor with Pixie)

Here are some generalities about editing photos on a computer. To make the most of your CPU and memory minimize the number of applications running. Unless you are on-line, you can temporarily disable your anti-virus software and firewall. Close any open Explorer windows and shut down your screen saver. Try looking at the applications in your System Tray (the right side of your Task Bar) and right-click on each to see if you can shut down these applications. They'll all come back when you restart your computer. Defrag your hard drive and empty the Clipboard; most photo editing programs make good use of this facility.

Finally, there is nothing like having a good photo with which to start.