Color modes are digital schemes that manage pixel depth information. For example, shown here is the grayscale image “Still Life.tif” opened in Photoshop. This particular image is an 8-bit channel, that was saved in the TIF format. In an 8-bit grayscale image, there are 256 levels of color value (in this case, gray) available for each picture element (pixel).
Therefore, each dot, or pixel, in this image can only be one of 256 different shades of gray, including black or white.
Fortunately, Photoshop gives us many ways However, there are other color modes available as well, some holding more data and some less. Let's take a look at some of the various available color modes.
Select the menu item Image>Mode to see your options. The first on the list is Bitmap.
We raster artists understand bitmapping to mean mapping pixels across a display, but the Bitmap mode is a 1-bit channel that allows you to work with only one bit of information: black or white. So describing tone becomes a function of placing dots of black on a white field.
Fortunately, Photoshop gives us many ways to describe value using only black and white, as you can see from the Method pop-up menu. We'll choose the first on the list to begin with.
Choose 50% Threshold and click OK. Here is our image converted to Bitmap The document’s storage size has been mode using this 50% Threshold method. reduced by about 80% as a bitmap mode Grayscale pixels become all white or all image over a grayscale mode image. black depending on how light or dark the Instead of having to keep track of 256 original pixels were. You may know this levels of gray, the program only applies 2: method by the name Line Art. black or white, known as 1-bit pixel depth. Choose Undo from the Edit menu to refer to the grayscale version and try the next method of bitmap conversion: Pattern Dither. This is a more sophisticated scheme that, instead of reading individual pixels in an image, reads Although a fast and efficient method of conversion that blocks of pixels, and attempts provides more visual information than the 50% Threshold to use a repeating pattern to method, and useful for certain design needs, still it lacks more closely approximate much in the way of "charm." It creates a visible grid multiple values. pattern that is too obtrusive for most routine uses. Again, choose Undo from the Edit menu, and let’s try one more. Diffusion Dither is the best method of converting an 8-bit channel to 1-bit, and is by far the most "intelligent" of the Line Art methods we have covered so far. Diffusion Dither breaks the images down into an invisible grid and This technique is very widely used, especially by designers wishing to applies uniformly sized reproduce a version of a grayscale or full color art for black and white dots of black across the printing or for Web-based publication quickly and inexpensively. It was image more closely also used in the early days of the Web as a quickly downloadable approximating the original. placeholder image for an RGB color version that took longer to transfer. Chose Save As from the File menu (or Save a appears, leave the Windows option selected. OS/ Copy, if that doesn’t work) and choose the BMP 2 is an ancient IBM legacy format that few people (Bit Map Picture) format from the pop-up menu use today. The 1 Bit pixel depth denotes the black- to save this bitmap Still Life image into your 4 or-white nature of the bitmap. Now choose OK, Colorization folder. Do not replace the original. and Still Life.bmp will join the original grayscale Click Save and in the BMP Options dialog that Still Life.tif file in the folder. Another economical way for designers to to launch the Duotone Options dialog. achieve a little color in an image is the Monotone is the default type of Duotone in the Duotone method. Of course, Duotone literally dialog. There is only one ink color available in means 2 colors, but Photoshop's Duotone mode a monotone image, but of course, Photoshop allows for the substitution of a single color, on will allow you to change the color “ink” if up to 4 colors (Quadtone). Revert to the you'd like. Simply click on the black color grayscale version of Still Life or reopen the TIF swatch to launch the Color Picker and choose original. Then select Image>Mode>Duotone... the hue you desire. In the Color Picker, choose a brown color that might work well in replacing the black ink of our monochrome image with a sepia- like tone. Experimentation gets you spectacular results sometimes that you would never expect. You also get spectacular failures too, sometimes, but relief is always just an Undo away!
After selecting the color, click OK to exit the Color Picker and return to the Duotone Options dialog. Now enter a new name for Ink 1. I have chosen "Sepia" as the name of this ink because the effect is that of a sepia-toned photograph. Click OK or press the Return (or Enter) key to see the results. The sepia-toned print, created with a monotone Duotone Mode, replaces all of the grayscale pixels with “sepia-scale” pixels. Only white remains unchanged. But there is a better way to add color. So for now, choose Undo from the Edit menu to revert to the grayscale version or close this file without saving and re- open the original Still Life TIF version. Let’s try a true Duotone. Photoshop duotones add a richness to images that one color alone can't provide. In essence, you are making 2 channels, each of which is 8-bits of pixel depth and each of which blend (or overprint) with the other. Select Duotone from Image>Mode menu. Then select Duotone from the Type window pop-up in the Duotone Options dialog. You should now see 2 color inks active in the Duotone Options dialog. Leave ink 1 as black (or change it back to black if you have to), and change ink 2 to the color of your choice.
Instead of using the standard color picker, try a color from the Color Libraries. Choose a "book" from the pop-up, like Pantone Coated, for example, and you can make sure your inks are exactly what a printer will have available for you. Here I have chosen a cool blue for the look of a selenium-toned image. The name of the color will be added to Ink 2. Next to the color swatch in the Duotone Options dialog is the Curves square. Curves lets you do just about any brightness correction you can imagine, if you take the time to learn its secrets.
First, click on the Curves square to access the Duotone Curve dialog. The diagonal line in the graph represents the range of black-to- white. Click and drag on the diagonal line in the Curves graph to "bend" the brightness/ darkness in the image from the point you click. You are remapping the amount of brightness the pixels of this intensity will have in the image.
Click again to place another point, and drag again. More pixels are remapped. Click on the gradient ramp below the curves to exchange the black and white positions in the graph. Save settings to load later, for use with other, similar images.
Professional designers like to save Duotone files in the EPS format, which nicely preserves Pantone, as well as other color information. The resulting duotone Still Life, colorized with cold selenium blue over a grayscale background. Experiment with the format. Try pushing the Curves values. You can achieve some remarkable results. Save your Duotone version of the Still Life in the to choose Photoshop EPS. In the EPS Options EPS (Encapsulated Post-Script) format (Still dialog, note the choices but leave the default Life.eps). Choose Save As… (or Save a Copy, if settings. Click OK to save into your project folder that doesn’t work) and pop-up the format menu with the other versions. ©2021 HARRY ST.OURS This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. All images and text by the author or used with permission, or under the Fair Use for Educators clause of the DMCA 2000. Brand names mentioned and logos displayed are the properties of their respective companies. All other rights reserved.