Editorial: A hopefully foolproof basic guide to submitting computer graphics

Like probably all journals, the European Journal of Entomology experiences frequent difficulties with authors who do not understand the computer graphic formats. This results in long and difficult discussions when we try to obtain their figures in a suitable electronic form, and since I usually become involved in those discussions sooner or later, I prepared the following text to help the authors to provide their graphics in a form we can use without performing breakneck transformations and without quality loss. Please note that all that follows concerns submission of final graphics for publication. Graphic files for reviewers may be of lower quality sufficient for evaluation of the results.

First, if your original figures are in a “hard” form (ink drawings on paper, photographic prints from negatives, photographic slides), we prefer receiving the original(s). Do not try to scan or otherwise digitalize the originals yourself unless you have considerable experience in that type of work; we will probably do it better.

If, on the other hand, the “originals” are electronic (e.g., photographs produced by digital cameras, or graphics constructed directly in computer programs), we need them in an electronic form. Printing such files and then scanning them again will invariably spoil them considerably. If you do not feel sure, it is better that you do not try to “improve” your digital photographs; we will do it here, and probably better. For example, if you overcontrast your photograph in a graphic editor so that the light shades are white and the dark shades are black, there is nothing we can do to improve it - a reversal is not possible as the information has been lost.

We generally accept graphics for publication only as bitmap files (I will get to that in a moment), preferably in the Tagged Image File Format (TIFF, the files end with the suffix .tif). Other acceptable formats are Adobe Photoshop (.psd) or simple bitmap format (typically ends with .bmp, but the files saved in that format are huge and generally unsuitable for sending via e-mail and I do not recommend it). Virtually every reasonably good graphic editor, both for PC and Macintosh, can save TIFF files, so I strongly recommend using this format. The popular JPEG format (files ending in .jpg) uses compression algorithms which produce very small files but sacrifice some quality. You can send those files if they originated as such (e.g., from a digital camera), but never save your images in that format after you have modified them since you degrade them with every save. Some bitmap formats may contain several superimposed separately editable “layers” (e.g., if you add lettering, it may be saved in a separate layer). You should check for presence of layers and “flatten” all layers into one before you submit the files.

As we cannot guarantee that other types of files will open in our software exactly as you see them in yours, we usually will not accept non-bitmap formats, such as vector graphics (e.g., .cdr files produced by Corel Draw or .ai files by Adobe Illustrator; if you for some reason really need to submit vector graphics, please negotiate that in advance with the editorial office), encapsulated postscript (.eps), Microsoft Excel (.xls), or Adobe Acrobat (.pdf); any proprietary Macintosh formats cannot be used even if they are bitmaps. Also, please never send your final graphics imported into a text (word processor) or presentation format, such as in the form of .doc or .ppt files - this really makes me feel depressed.

Computer files are digital - nothing new. In the case of bitmap files, the picture consists of a rectangular network of small squares (called pixels) which are homogeneous and cannot be divided further (well, they can, but you will not obtain more detail). Open one of your bitmap files and enlarge it as far as your editor will permit and you will see what I mean. Therefore, if you once save your digital image in a bitmap file with low resolution (low number of pixels), there is no point in trying to enlarge it electronically - the information simply is not there. Keep that in mind.

Basically, your images may be line art, black and white halftones, or color. Correspondingly, you can save your .tif or .psd bitmaps in three modes (there are more, but we accept those three which are the most common). In the first mode (also called “bitmap” in Adobe Photoshop, which is somewhat confusing), your pixels can be only white or black (that means one bit of information for each pixel, but forget that if you do not know what a bit is). Save your line art in that format since your files will be much smaller. You can save line art in the following two modes as well, but you unnecessarily waste space and get nothing (in the better case, in the worst you may spoil the clarity and sharpness of details). The second mode is called “grayscale” in most editors, and every pixel can have one of 256 levels of gray, from completely white to completely black (that means 8 bits per pixel, in case you wondered). Save your black and white photographs, or any graphics that have levels of gray but no color, in that mode. Finally, the mode that we require for color graphics is called “RGB”, an abbreviation of Red, Green and Blue, the three color channels composing the final color of each pixel. This format takes much more space because, in an uncompressed form at least, it requires 24 bits (8 per each color channel) of information to define the color of each pixel (let’s not go into further detail). Therefore use of this mode for saving grayscale or even line art graphics is suicidal.

Uncompressed TIFF files are about as large as simple bitmap files (and that means very large). However, better graphic editors offer an option of internal LZW compression of TIFF files (a compression algorithm introduced by Abraham Lempel, Jacob Ziv and Terry Welch). Unlike JPEG which, particularly at higher compression levels, causes considerable quality loss, the LZW compression is “lossless” and you can safely enable it to make your TIFF files slightly to considerably smaller (depends on the complexity of your picture). In some Adobe Photoshop versions you are also offered a possibility of internal JPEG compression of TIFF files - please never use that option.

Now we come to the magical and so often misunderstood word “resolution”. Basically, this means the number of pixels there are per linear unit of the image. Traditionally, this is measured in pixels per inch (the abbreviation “dpi” is basically the same thing, meaning “dots per inch”). Per inch of printed (or displayed) image, that is - the word “resolution” actually has no meaning until you define how large the printed image will be. Nothing can prevent you from printing a given computer image as large or small as you choose, and yet the total number of pixels in that image will remain the same and therefore the resolution will be different for each print size. Although the EJE is no longer produced in printed form, you can print the PDF and if you do that at a 1:1 ratio, the printed page will be 170 mm wide and 247 mm long - the “print size” below refers to those measurements.

The EJE requires the following resolutions for the three above mentioned modes: Line art (1 bit): 1,200 dpi at print size (600 dpi as a minimum for schemes, graphs, etc.). Grayscale (8 bit): 300–400 dpi at print size. RGB color (24 bit): 300–400 dpi at print size. Considerably higher resolution makes the files very large and will be reduced to the above values in the final PDF.

If you are still confused, an example might help. Let’s suppose that you have a grayscale photograph that has 1,600 horizontal and 1,200 vertical pixels (if you do the multiplication, you will see that this image has approximately two millions of total pixels - this is what you get from an ancient 2-megapixel digital camera). Information about image size in pixels for a given file can be obtained in any serious graphic editor - in Adobe Photoshop, for instance, open the file and go to Image, Image size. So how large can your 1600x1200 dpi image be if you require 400 dpi for good quality? Obviously 4 inches (about 10 cm) wide and 3 inches (cca 7.5 cm) high, so it cannot fill the entire page width. A single picture that should fill the entire page width (170 mm, about 6.8 inches) should be about 2,700 pixels wide. Such picture can be produced by a 6-megapixel camera. Current (2015) commercial digital cameras usually can produce images of 10 megapixels or more if you save your photographs at the camera’s full resolution, although microscopic cameras usually still have a lower resolution to produce images with less noise even at poor light conditions.

If you have read this far, I thank you for your patience and for submitting your graphics to the EJE in suitable form and quality.

Petr Svacha