Bits and Pixels



Of Bits, Pixels, DPIs, Ditherings, Fargo & Turbo-Speed-Print

A Technical Bulletin written in the form of a play, to shed some light on a subject found boring by some and forbidding by others. Equally aimed at showing the virtues of printing with the Fargo Primera Pro and the Turbo-Speed-Print software

• Thyrsus, a Greek shepherd caught in the downsizing of the agro-business by the Olympian Gods, is thinking about another activity
• Eurydia, a Nymph in the retinue of Callisto, a female Pythagorean and foundress of the first "I love Pythagoras" fan club..
• The Dithering Magician.

The location: hills and woods near Corynth, Greece.

Thyrsus (talking to himself). Oh how I wish I could get into art and multimedia. I know I have an artistic disposition, maybe I could create pictures, print them, put them on T-shirts or mugs and sell shirts and mugs to the tourists at the Saturday market in Corynth. I know that once I have a print it is quite easy to transfer it to another medium. But when it comes to printing I become confused. The manufacturers use terms that have a ring of familiarity, bits, pixels, resolution, etc., but when I try to understand the process my mind goes into a spin - it almost hurts.

Eurydia (jumping out of a bush). Thyrsus, I know the problem and I am here to help you. We will try to compare, as much as possible, the alchemy of printing to a process we are all familiar with, for example the creation of a mosaic. I will start by showing you a picture on my monitor, a picture represented by 640 horizontal pixels and 697 vertical pixels. It is a full screen picture. These pixels are squarelets that you can only see when I enlarge the picture using the ‘zoom’ function. Now this picture was transferred from the real thing to the screen using a resolution of 75 dots per inch (dpi). In other words, it is as if you had divided every inch of the original image into 75 parts and converted all these individual parts into the pixels on the screen.

Are we clear so far?

Thyrsus: yes

Eurydia I will also tell you that the picture on the screen is represented using a palette of 16.7 million colors. This is the same as saying that we have a ’24 bit’ image but we will discuss later this equivalence of meaning. Now imagine you wish to convert the picture on the screen into a pretty mosaic. Out of my imaginary tile drawer I will allow you 75 mini-tiles for every inch of your mosaic (print).

Thyrsus. How large will be the finished mosaic, then?

Eurydia Simple. Divide the 640 horizontal pixels by 75, 640/75= about 8.5" and the vertical pixels by 75, 697/75= about 9.3 inches.

Thyrsus. But that just happens to be a full printed page.

Eurydia You are right Thyrsus. A screen picture of 640 x 697 pixels, when printed at 75 dpi will fill a page.

Thyrsus. One moment please, you said you will allow me 75 dots for every inch but how about colors? In other words how many different color tiles do I have available to represent the 16.7 million colors of the original image?

Eurydia This is a very important question and I want the Dithering Magician to answer you directly. Using his magic power the Dithering Magician can take a printer that can only print with 16 basic colors and make it print as if it had 16.7 million colors.

(Eurydia and Thyrsus enter the cave. The Dithering Magician is sitting on a stalagmite with a flat top. He wears a long robe completely covered with multicolored beads).

Dithering Magician. I guess why you are here, Thyrsus, and I know your question. Dithering may not be as difficult as you think, but I must ask you first: Do you realize that color is reproduced by a combination of the basic colors red, green and blue?

Thyrsus. Yes I do.

Dithering Magician. Well then, if I have at hand 256 grades of red, 256 of yellow and 256 of blue, I will have a total of 256 x 256 x 256 = 16.7 million colors, right?

Thyrsus. Yes, I tried it on my calculator and I have seen that you are right.

Dithering Magician. But the Fargo Primera Pro, which you are coveting, (as well as other printers working on the same principle), has only 16 grades of red, green and blue. This means that the Fargo has available 16 x 16 x 16 = 4096 colors rather than all those millions.

Thyrsus. But how can you print with 16.7 million colors (as the Fargo literature says) when the printer has so many fewer colors?

Dithering Magician. With my magic.

Thyrsus. Surely you cannot, by magic, create colors that don’t exist.

Dithering Magician. No, but I can make up for the reduced colors with increased resolution.

Thyrsus. What do you mean?

Dithering Magician. We started by agreeing that to get to the 16.7 million colors we need 256 grades of each of the (3) component colors. Now, if I have only 16 basic colors this means that I have only available 16/256 = 1/16th of the necessary colors. But I can compensate by reproducing each pixel with a mini-tile whose sides are made up of (4) dots (or (4) even smaller mini-tiles, if you wish to preserve the analogy). The total number of smaller mini-tiles making up the bigger mini-tile is then 4x4=16. We can say that my 16-times reduction in the number of available colors has been made up by a 4-times increase in resolution.

Thyrsus. I see but you talked about a mini-tile made up of 4x4=16 smaller dots (or mini-tiles). Should you not say then, that the resolution has been increased 16 times?

Dithering Magician. No, you use the linear measure of the side (i.e. (4) dots per inch) to define the resolution, or, in this case, the increase in resolution. Just as when you talk about the printer, you say that a printer has a resolution of 300 dpi, not a resolution of 300x300=90,000.

This process of stretching a pixel into a block made up of multiple component dots is called "DITHERING" from which I also get my name. So, if my original pixel has a color that the printer does not have, that color will be reproduced by a combination of the 4 x 4 = 16 dots that we created when we increased the resolution.

If you have (16) of each fundamental color, blue, yellow and red plus you further combine them in 16 different ways (due to the increased resolution), then you get (16) red x (16) yellow) x 16 (blue) x 16 (added combination) = (see the magic) 16.7 million colors.

Thyrsus. That is really magic, but tell me Dithering Magician, with all this dithering magic do we not give up something somewhere?

Dithering Magician. Right you are, Thyrsus - there is no free lunch even with Dithering Magicians. But now it is time for me to retire and concentrate on this new algorithm I have thought about. Eurydia, your Nymph can take over now and discuss with you how the Fargo Primera works and why Turbo-Speed-Print makes it work that much better.

Thyrsus. Thank you, Dithering Magician. (Eurydia and Thyrsus exit the cave into the fresh mountain air) . Now, dear Eurydia, how can we put together these (3) concepts, resolution, dithering, dots per inch (or mini-tiles per inch) and make heads or tail of this mental soup?

Eurydia Do you remember that at the beginning I gave you 75 mini-tiles for every inch of the picture that you wanted to print or turn into a mosaic?

Thyrsus. Yes.

Eurydia And do you remember that we started with a picture represented with 640 x 697 pixels, which, converted into a print or mosaic, built with 75 dots or mini-tiles per inch, would give you a picture of 8.5" x 9.3" dimensions?

Thyrsus. Yes I remember this also.

Eurydia Now think of the printed page from Fargo as a mould with holes. Each hole must be filled with a mini-tile. The Fargo mould has 300 mini-tiles per inch (i.e. prints at 300 dots per inch). In mosaic terms you must use 300 mini-tiles for every inch of mould.

Thyrsus What happens then?

Eurydia Well, I told you that by using 75 mini-tiles per inch you would create a mosaic with dimensions 8.5 x 9.3". If you actually use 300 mini-tiles per inch then the printed picture or mosaic will shrink by a factor of 4. The end result will be a picture or a mosaic with dimensions 8.5/4= 2.12" x 9.3/4=2.3".

Thyrsus. But I cannot sell such a small artifact at the Saturday market in Corynth. The tourists, especially the Americans, always think that bigger is better.

Eurydia I understand. What you can do, with your mould, is to fill each bunch of consecutive (4) holes (in the vertical and horizontal direction) with (4) identical mini-tiles, or (1) mini-tile repeated (4) times. To do this I will have to quadruple the number of tiles per inch I gave you at the beginning (75 x 4 = 300), but note this - for every inch there will only be 75 mini-tiles that are different, or better, that really represent the original picture. The others 300-75=225 are but repeats or doubles.

Thyrsus. What is the consequence of this?

Eurydia That horrible, unnatural visual effect called pixellation, or ragged edges, or staircase effect - what makes people say: "that is not a real picture, it is a computer picture".

Thyrsus. Is there a way out then?

Eurydia There is, but by using the Fargo Printer driver alone, there is a price to pay. If you have followed me so far I will show you in a moment why Turbo-Speed-Print will give you a solution without paying the price.

Thyrsus. Tell me first what is the way out and what I am sacrificing when I use the Fargo driver.

Eurydia You will remember again that the original picture I gave you was obtained with 75 dots per inch?

Thyrsus. Yes, I remember.

Eurydia You can simply increase the resolution used to convert the original picture into the computer image on your screen. Rather than 75 dots per inch, you can use 150, or 300 dpi. However, if you use 150 dpi, you will still see pixellation. At 300 dpi the pixellation is essentially eliminated.

Thyrsus. But how can I convert a 75 dots per inch image on screen into the same image but represented at 150 or 300 dpi?

Eurydia Image Processing programs show you a method to do so. You must be very familiar with the programs, however, because there is no such menu item in the program called "double or quadruple the resolution". But it can be done.

Thyrsus. Well, if I learn how to increase the resolution, why should not anyone rush immediately to do so every time they print? Is there anything to lose?

Eurydia There is. You pay a price in preparation time and hard disk space.

Thyrsus. How come?

Eurydia A 75 dpi full screen image takes 1.34 meg of disk space, a 150 dpi image takes 5.35 meg, a 300 dpi image tales a whopping 21.4 meg of disk space. The table shows how these file sizes are calculated, but for the moment I just want you to understand the key concept.

Thyrsus. And how about preparation time?

Eurydia Preparation time is the sum of (2) contributions:

the time the computer needs to increase the resolution. This varies depending on how fast your computer is, but it may take up to (2) minutes or more, per picture.

The time for the computer to convert the data into a format for the Fargo printer to print. Refer to table (A) for reference.

Thyrsus. But to avoid the computer time spent in increasing the resolution, could I not, for example, scan a picture already at, say, 300 or 600 dpi?

Eurydia You could, but keep in mind two things.

Scanning a full page at 300 dpi in 24 bit color is even a lengthier process than having the computer increase the resolution of a picture already acquired on screen and...

Many programs just do not like large scanned files - they crash more often than not. Users do not realize this because they rarely scan a full page at high resolution in color, due to the excruciating length of time involved.

Thyrsus. What happens if, instead of a scanner I use a camera?

Eurydia A camera typically captures a picture at an equivalent resolution of 75 dpi and we are back at the proverbial square one.

Thyrsus. How can Turbo-Speed-Print help then?

Eurydia TURBO-SPEED-PRINT uses a new technology and a new algorithm, whereby you DO NOT NEED to have the computer increase the resolution before you can print. So you start with a 75 dpi file that takes only 1 meg of space and end up with a print that looks as if you started with a file of 300 dpi resolution. So you save:

• preparation time
• print time
• disk space

The comparison table will give you a good reference

Thyrsus. I see, but what is the meaning of the column 300 x 600?

Eurydia In an attempt to improve the picture quality the Fargo driver features an increase in the vertical resolution, but TURBO-SPEED-PRINT pictures are qualitatively better than even those printed at 300 x 600. Besides in the 300 x 600 mode the time for printing is further increased.

Thyrsus. All right, now let me repeat the essentials and tell me if I have understood.

1. If I print a 75 dpi (full page) file and I want to avoid pixellation, I must increase the resolution of the ORIGINAL file to 300 dpi.
2. I can do this by computer but it takes time and it increases dramatically the amount of disk space required to store the file.
3. Because preparation time depends on the size of the file to print, the bigger the file the longer the preparation time.
4. TURBO-SPEED-PRINT can work from a 75 dpi file and do the trick of increasing the resolution with the net effect of dramatically shortening preparation time, reducing print time, eliminating pixellation and the need of massive hard disk space.

Eurydia Correct. But the benefits of TURBO-SPEED-PRINT are not finished. Say you have more than one image to print (or more than a mosaic to make at a time). Without TURBO-SPEED-PRINT you would have to remain for hours glued to the computer, waiting for it to become free again to print the next picture. And printing in the background with the huge files required for higher resolution is to all effects impractical. If you have, say, 10 images which you MUST have pre-massaged to increase the resolution, those prints alone will mobilize about 220 meg of hard disk space, plus 35 meg needed for the temporary files the Fargo creates while printing.

TURBO-SPEED-PRINT, instead, lets you ‘batch’ the files to be printed (up to 50). Batching means putting all the files to print into one file and printing them all together with (1) command. Furthermore TURBO-SPEED-PRINT lets you index each file and catalog it in a way that is efficient, practical and user friendly. And, for comparison, (10) pictures will only take 15 meg of disk space (plus the 35 meg for temporary files needed by the Fargo driver).

Thyrsus. Now I see why batch printing is useful. So, for example, let’s say that I plan to sell (50) pictures to the tourists at the Saturday market. With the standard Fargo software the time needed would be:

• (10) minutes to select and acquire the picture on screen
• (40) min for a good quality picture to be printed. Hence 50 x 50 = 2500 min / 60 = almost 42 hours. And because I need to be there to load the pictures to be printed, I would have to work (5) days to prepare for my Saturday sale-a-thon.

Instead with TURBO-SPEED-PRINT it would take me:

• 10 minutes to select and acquire the picture on screen.
• 14 min to print it but I can batch them.

So to get (50) pictures ready it would take me:

(10 x 50) minutes for picture selection and preparation = just over 8 hours

Then I would have the pictures printed during the night. So with TURBO-SPEED-PRINT I will reduce my work load from one week down to one day. I may use the spare time to play golf with my friend Rubicus.

Anything else left to say about TURBO-SPEED-PRINT?

Eurydia Yes, you can include up to (4) images on the same page. And.... very important once you start doing it, you have a faithful, precise and measured correspondence between the position of the image on the screen and the position of the image on the paper. So, for example, if you wish to transfer images to mugs you can bunch (4) images on one sheet, thus reducing the cost of supplies by a factor of (4).

Thyrsus. One last question, if we can do all these good things in sublimation mode, why cannot we do something similar in the standard thermal mode?

Eurydia Because in the standard mode the colors available for printing are 8, that is, 2 shades for each red, yellow and blue. Now if you remember the tricks of the Dithering Magician we see that if I only have (2) color grades then I reduce the color resolution by 256/2=128 times, where 256 is the number of colors required (for each red, yellow, blue) to achieve 16.7 million colors.

A 128 times reduction in colors means that, through dithering I would have to increase the resolution 11 times to achieve 24 bit color performance (11.31 x 11.31 = 128 - refer to the previous calculation and reasoning where we achieved 24 bit color by increasing the resolution 4 times).

Now then, if we start with a 75 dpi resolution and increase it 11 times we get 75 x 11 = 825 dpi. In other words we should print at 825 dpi in order to get all the colors. But we saw that printing at 300 dpi starting from a 75 dpi image created pixellation. Increasing the printing resolution 11 times would turn the picture into a blob.

You can show the same thing in another equivalent way.

To print at 300 dpi and have true color, we would have to start with a picture having resolution of 300/11 = 27 dpi where 300 is the Fargo print resolution and 11 is the factor by which we must increase the resolution of the original picture to get a full color print. But a 27 dpi image would not look very good even on the screen.

Thyrsus. Is there a solution then?

Eurydia Yes, and the solution is called compromise. When printing in standard thermal mode Fargo reduces the number of colors dramatically. This is the reason why printing in sublimation mode is said to be ‘photo-realistic", because you have the effect of 16.7 million colors. In standard thermal mode you print with a total number of 32,768 colors. The calculations will fix the idea in mind once and for all:

1. The Fargo must print at 300 dpi so the number cannot be changed.
2. I start with a 75 dpi picture on screen. To print it at 300 dpi I must increase the resolution 4 times.
3. But we saw that 256 (number of color grades required (for each red, blue, yellow) to achieve 16.7 million, divided by the number of colors available to the printer (that is 2) , gave us the factor required to calculate the necessary increase in resolution to make up for the limited number of ‘primary’ colors available
4. Here we know that the primary colors available are (2). We also know that to print at 300 dpi from a 75 dpi screen image we must increase the resolution (4) times. Now then, the number of final colors used in the picture will be (2) (colors available) x 16 (expressing that the resolution has been increased 4 times, 4x4=16). And, as we know 16 x 2 = 32. Et voila’, in the standard mode the Fargo prints with 32 color grades for each red, yellow and blue. Hence the total number of colors is 32x32x32=32,768.

Thyrsus. But why we don’t use TURBO-SPEED-PRINT also in the standard mode?

Eurydia Because lower number of colors means lower size files and the original Fargo algorithm works well enough.

Thyrsus. Thank you Eurydia. The moral of the story is then:

1. Use TURBO-SPEED-PRINT in sublimation mode and
2. Cut dramatically preparation and print time
3. Improve utilization of disk space
4. Save time by printing in batches
5. Eliminate pixellation and get a true photographic quality print
6. Put up to (4) pictures on the same page thus saving on supplies.

Eurydia You got it Thyrsus. Best of luck on your new multimedia venture and don’t forget to call Computer Friends for all your Heat Transfer needs. They have complete Heat Transfer systems, individual modules and supplies And........ they also have a version of TURBO-SPEED-PRINT for Fargo Foto-Fun.

Eurydia fades away into a rainbow. Thyrsus rushes to Corynth and calls Computer Friends to order the Fargo Primera with Turbo-Speed-Print (1-503-626-2291).

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