This is what I’ve done so far: I have several photographs of blood cells. photographed all the blood cells at the same magnification (100x oil) using the same lighting conditions; they are currently saved as jpgs.
You’ve already started down the wrong path. JPEG uses "lossy" compression; that means it deliberately degrades the image in order to save space on disk. JPEG is only appropriate for situations where file size on disk is important and image quality is not important. It is not generally appropriate for images destined for professional printing.
I need to have pictures that are 19 picas wide (or 80
mm). I am interested in showing only a small area of each photomicrograph, so I want to crop the images that I have, and keep them all exactly the same size when I’m done (and thus the magnification will be equal across all pictures).
What size are they now? What resolution are they now?
You can crop the image using the crop tool or marquee tool, then use the Image Size command (with the "Resample Image" checkbox turned OFF) to make the images 80mm wide. However, depending on how the image was originally created, this may produce an image that is too low in resolution. It should be at least 300 pixels per inch *at the final size.*
You can turn on "Resample Image" in the Image Size dialog and make the resolution be 300 pixels per inch, but you can never create detail that is not present in the original by doing this; the results will not be better. You need to CREATE the image with enough resolution in the first place!
The color images need to be submitted in CMYK format (which I figured out how to do on the Photoshop menu).
HOW are you converting to CMYK? What kind of paper will the images be printed on? This is important stuff! You can’t blindly go Image->Mode->CMYK and end up with something that will be printable on any kind of paper and press.
For best results, you MUST use File->Color Settings->CMYK Setup, and use the CMYK Setup dialog box to specify the separation parameters for your press and paper, EVERY time you create a CMYK separation.
Also, many colors in RGB can not be reproduced in CMYK. CMYK has a different range of colors, or "gamut," than RGB.
If your image contains out-of-gamut colors, these colors will be converted to their nearest approximation in CMYK. The result will be a color which is less saturated and somewhat flatter.
Often, a little bit of color tweaking is necessary in the CMYK image. After separating an RGB image to CMYK, you may wish to use the Curves command (Image->Adjust->Curves) to increase contrast in the midtones slightly, as the separation often becomes flatter in the midtones.
Specific colors can be tweaked with Image->Adjust->Selective Color. For example, if your blues have yellow in them, you can remove yellow from blues to make them more saturated and richer.
When you color corrrect the image, you should, of course, have your Info palette open. Look at the numbers in the out-of-gamut colors; see if your primary colors have any contaminating color that can be reduced to increase saturation. For example, yellow in your blues or cyan in your reds can be reduced, if present, to make the colors richer.
Vivid RGB blues often separate with too much magenta, making the colors appear more purple than blue. Using Selective Color to reduce magenta in blues will often solve this problem.
The range and depth of color you can expect to get depends on the settings in your CMYK setup, which themselves depend on the kind of paper and press you are going to be printing on.
As for setting up your CMYK separation:
If you just go Image->Mode->CMYK without changing the values in your CMYK setup, the result will look okay on most sheetfed presses and coated (glossy) color stocks, but will not be acceptable for, say, newspaper printing.
For best results, you should talk to your printer about what to do. Most importantly, make sure he gives you the values he needs for maximum ink and maximum black percentages; if you exceed these values, the image may smear on press.
As starter points:
For sheetfed presses printing on high-quality coated paper, you can usually use GCR, 100% black ink limit, 300% total ink limit, Light or Medium black generation.
For very high quality lithographic output, your total ink limit can go as high as 310%.
For web-fed presses on glossy paper, or sheetfed presses using high-quality uncoated paper at a 110-line halftone or above, use GCR, 100% black ink limit, 280% total ink limit, Light or Medium black generation.
Newsprint is a different story entirely. For newsprint, appropriate settings might be UCR, 240% to 260% total ink limit, 85% black ink limit. When you convert the image to CMYK, it will look washed-out and flat, but newsprint darkens *considerably* on press so this reduction in density is necessary.
Assuming I don’t do a lot of touchup (just autocolor), it seems that I could do this as a cookbook exercise, if I only knew how to do it (do I guesstimate the millimeters using the tool bars?
You crop whatever area you want, with no regard for size. Then you use Image Size with Resample Image OFF to make the image exactly 80MM wide.
Once I crop an
area, how do I save it?
File->Save As. For print, do not use JPEG. Use TIFF.
Do I crop, then autocolor, then change to
CMYK? Another order?
Generally speaking, you do coarse color correction on the original, convert to CMYK, do final color correction there, crop, unsharp mask, and save for print. Unsharp masking is used to sharpen the image; any image destined for press will benefit from sharpening using Unsharp Mask.
Unsharp masking is part art, part science. There is no set way to use it which works for all images.
Generally speaking, however:
The Unsharp Mask filter works by exaggerating areas of high contrast–ie, edges. This gives the appearance of sharper edges, and increases the apparent overall sharpness of the image. While it can’t make a blurred or out-of-focus image sharp (nothing can do this), it can dramatically increase the perception of sharpness. And unsharp masking is a requirement to get good-looking images in print.
The Amount slider dictates how much edges are increased in contrast. If the value in this slider is too high, the image will appear to have "halos" around the edges.
The Radius slider determines how wide the area of enhanced contrast is around edges. In general, the amount you put in the Radius field depends on the resolution of the image; the higher the resolution in pixels per inch, the wider the Radius.
A good place to start is (image resolution/200). If the image is screen resolution–100 pixels per inch or less–try a Radius of 1. Increasin ghte Radius will also create undesireable halos around edges.
If you are sharpening an image which will be printed on a printing press, and your image is the recommended resolution (twice the frequency of the halftone you will be using to reproduce the image on press), use a Radius of (halftone screen/100). So, for example, if your image is being printed on press with a 150-line-per-inch halftone, use a Radius value of 1.5.
The Threshold command determines how far apart two neighboring pixels must be in tonal value in order to be sharpened. I usually start with a Threshold of 3. Lower Threshold values exaggerate noise along with edges; higher values don’t sharpen noise, but also produce more muted sharpening overall.
Note that if your image is intended for print, you should set the Amount value so that the image looks slightly over-sharpened on your screen! This is because the process of halftoning the image for print decreases the apparent sharpness of the image (which is why all images should have USM applied if they are going to be used for print).
Hope that helps!
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