How to Use Bitmap Mode in Photoshop

Of all the image modes in Photoshop, perhaps the least used today is Bitmap mode. It’s the “true” black-and-white mode, unlike Grayscale, which is what a “black-and-white” photograph really is. And Bitmap actually has a couple of advantages, though making proper use of the mode does take a little understanding.

A color picture first has to be changed to Grayscale mode to drop color out, and then one can convert to Bitmap. (If the user knows the image is going to be put in Bitmap, it’s advisable to keep it fairly high-resolution; since Bitmap only has two colors—black and white—compensating with more pixels helps keep the image from looking too grainy.) There are a couple of other things one can do to make a grayscale image better, but that’s another story.

Color Picture Convert Arrow Grayscale Picture

When Bitmap mode is called up, another dialog box asks a couple of questions. One is about resolution—usually this should not be changed. If the image already has adequate detail, it should be left alone. Increasing the resolution should be done beforehand, if at all.

Bitmap Dialog Box

The other is “Method”—how should the pixels be handled? This is the real question, as it affects the final appearance the most.

The first choice, 50% Threshold, looks at all the pixels in the image and applies a straightforward rule: If the brightness of the pixel is 128 or less, it turns black. If 129 or more (the possible range is from 0 to 255), it turns white. But this makes the picture look very harsh and blotchy, as it doesn’t take shading or grays into account.

50% Threshold Picture

The next choice, Pattern Dither, sort of does this. It tries to distribute black and white pixels a little more evenly (in a pattern, hence the name), and can create a fairly “readable” image provided the resolution is not too low. Some people consider this to look artistic, and in some cases the image turns out pretty well.

Pattern Dither Picture

Diffusion Dither, though, is a better choice for a result which looks more realistic. “Diffusion” means the pixels are scattered semi-randomly, the same way perfume gradually drifts through the air. “Dither” is defined as “The use of dot patterns to approximate colors not available in the palette.” (Wiktionary)

Diffusion Dither Picture

Halftone Screen is another matter, and produces something else again. Half-toning was used for a long time in producing newspaper photographs such that they looked like “true” grayscale images. What half-toning really does is to remake the image as a regularly-spaced pattern of dots of varying size to simulate grayscale, rather than bunching them together to make darker (or lighter, by spreading them apart) grays. How often this comes up today depends on what the print medium is going to be, but it’s not as useful for onscreen or conventional computer printing these days since half-tone techniques were developed partly to allow for rapid mass printing (newspapers, magazines) with relatively low-res, high-speed (therefore less expensive) processes.

Halftone Dialog Box Halftone Picture

The advantages to Bitmap mode are, first, it brings the file size WAY down, sometimes only a couple percent as big as the color version, or even less. (Only two colors, after all.) Ditto the grayscale version. Second, though it won’t have color, the detail and simulated gray shades can look almost as good as a true grayscale image, and take a lot less time to print. And finally, it’ll look decent on any printer, color or no. Picking the method is the only thing one usually has to worry about, and often the choice simply depends on the desired final use.

Feathering a Selection in Photoshop

One of the must-have skills in Photoshop is the ability to make precise selections, since we indicate which parts of the picture we want to work with this way, and there are a number of techniques to do it. But equally important is the ability to feather, or “fuzz” the edge of the selection. Very few normal photographs are going to be so supremely razor-sharp in focus that a selection needs to be also, and even those that are will often not be super-high-resolution (that is, naturally a tiny bit fuzzy) anyway. Aside from any specific effects you want to achieve….

Open File

Once you open your file, you can start by making a rough selection with any tool—say, the Magic Wand or the Lasso. Then, either hold down the Shift key or select the Add to Selection button in the tool’s Options at top, and click or drag as needed to add the bits you want. (I admit I like the Magic Wand for a good many items, as it lets me make color-based selections quickly.)

Selection Made

Then, having made and fine-tuned the selection, we go to the Select menu, slide down to Modify, and click Feather in the submenu.

Select Menu Modify Feather Dialog Box

The number of pixels of feather you want to use will depend on a few things: The resolution of the image (the higher the res, the lower the feather number), the area you selected (larger selection=lower feather, generally), and what you want to do with the selected area (you tell me 🙂 ). For things like tinting, a lower number is usually better as you don’t want it to look like smeared paint. For blending effects like softening filters or other non-color-related ideas, a higher number would be good to soften the edge (romantic-portrait-type photos, for example).

It’s a simple effect, but a powerful one. And it doesn’t take too much practice to get a nice result. Besides, you can make a copy of the layer in question and play around with it till you get a good combination, then apply to the final draft.

Clone Stamping in Photoshop

The use of the Clone Stamp tool, in itself, is not hard to understand. It allows the user to “borrow” or copy a piece of picture from one spot to “clone” or paste elsewhere. But some people use it like a paintbrush, and clone big swaths of picture from one place to another—which looks obviously like cloning, or stereotypical “Photoshopping”.

So is there a trick to using the tool and not making things look visibly cloned? Actually, there is. It’s a little bit more work, but it’s not really difficult. It does depend somewhat on the picture and your goals.

Elephant

Once you open the picture, examine it to see where you want to borrow from and copy to. (Here I use the example of making an elephant disappear—it’d be a cool stage illusion….)

Luckily, the surroundings lend themselves to the effect I’m going for. I start by setting the size of the tool, not too big, and the hardness (how sharp the edge is) to zero, so it blends nicely.

Clone Stamp Tool Settings

I do an Alt-click where I want to borrow from, then use a few clicks to “paste” from that area over the image of the elephant. Alt-click again, from a slightly different area, a few more regular clicks on the elephant, and continue on, each time starting with a different patch, till the modification is done.

Clone Stamping

The real trick—the main point of this kind of exercise—is to borrow a little from here, a little from there. Create the cloned area as a sort of patchwork, to get a somewhat random choice of bits from the “copy” area so the “paste” area actually consists of many small ones, chosen from no one particular part.

Mostly Gone

There is also some technique to clone stamping like this—some study of the image to determine which parts to borrow from and clone to, exactly how big the tool area should be based on the image and its resolution, and so on. But the main thing is to do a little at a time, and not too much from any one area. Nature is usually pretty random when she paints, so following her precept can give you a natural-looking result.

RGB vs CMYK–Which should I use?

Having taught and worked with Adobe Photoshop for many years, I get asked many basic but good questions about it by new users. One has to do with color, and the color systems we use in a picture. There are several that Photoshop can use, but the two most common are RGB and CMYK. The question: Which is best?

The fundamental difference between the two is, RGB is meant for use on screen, and CMYK for print. The terms used to describe how they work are “additive primaries” and “subtractive primaries”, which refer to how these systems show white. For RGB, imagine standing in a dark room with a white wall. Take three flashlights, with color filters (red, green, and blue) and shine them on the wall. Where the three colors overlap, they seem to make white light (the opposite of what a prism does with white light—see Pink Floyd’s album THE DARK SIDE OF THE MOON, specifically the cover—and the back cover.) So the three additive primaries add up to white.

Additive Primaries

With CMYK, the example is even simpler—a piece of paper going through a color printer may have areas where no ink or toner has landed. And the color of the paper we usually use? White, of course. So when the colors are held back, or subtracted, from a spot on the paper, that spot stays (or is) white.

Subtractive Primaries

But we need black ink too, because the dyes or pigments only sorta make black, and a normal eye can see this. So the printing folks added it for completeness.

In doing this, though, we get a couple of problems, and it takes a little thought to get round them. First, because the RGB system normally involves a screen that illuminates itself, it can show more subtle shadings of color than a piece of printed paper (which, unless you’re using radioactive inks—shame on you!—does NOT glow in the dark). The term Photoshoppers and graphic artists use is the “gamut”, which is wider/larger for RGB than for CMYK (where the ink/toner can smear a tiny bit and mess up the shadings). And a printout can’t show all the shades that a screen can. By definition, therefore, printout will always look a little less intense (“saturated”) than onscreen images.

Color Gamuts

And second, any Photoshop image saved in the CMYK system will use 33% more space on disk, regardless, than if saved with RGB. Why? Because the number of color “channels”, how many kinds of color there are in the picture at minimum, is three for RGB, and four with CMYK.

So which should we use?

If you’re scanning in a photograph you want to clean up and reprint (say, from the early 1900s), CMYK will work better, because what you’ll see on screen is what will come out of the printer. But if you’re scanning for archival purposes, scan in CMYK if possible to get a realistic version of the image, THEN change to RGB. Since RGB’s gamut is wider than CMYK’s you won’t lose any subtleties or shadings, but you will get a smaller file on disk. And you can scan in CMYK, do all your work, then save in RGB for later. Best of both worlds. Just have to make sure we understand the tradeoff of size, gamut, and storability.

Free Adobe Photoshop Tutorials

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