LZW Compression File Prep for Letterpress Plates

For Adobe enthusiasts who use Photoshop to create their platemaking files, we’d like to introduce you to Lempel-Ziv-Welch, which is a simple algorithm known as LZW compression. LZW compression makes your file size smaller without losing any image quality. Have a 1200 dpi, 22 megabyte file? No problem with LZW compression. It can compress that file down to mere megabytes and sometimes even kilobytes. Why do you want higher resolution? So you can have text and images that are higher quality and pleasing to the eye when printed.

Here is how you use the gem that is LZW. If you have a Photoshop image or text that you need to bitmap for a platemaking line art file, follow these steps.

1. Open your file in Adobe Photoshop. Convert to grayscale via IMAGE > MODE > GRAYSCALE. Select Yes if a window asks about discarding color.

2. Check your image size via IMAGE > IMAGE SIZE. When this window opens up, make note of the Pixel Dimensions at the top. Look halfway down the page at the Resolution of Pixels/Inch. Is the number 300 or less? We can do better! Increasing your resolution can shave and smooth out the pixelation of your bitmapped image. Change your resolution to between 600 – 1200.

Adobe Photoshop file showing how to check image size resolution.



Did you see your Pixel Dimension make a big jump up? Don’t worry, LZW will take care of that later. Click OK to save this new setting.

3. Select LAYER > check to see if Flatten Image is showing. If yes, Click on this.

4. Click on IMAGE > MODE > BITMAP. A window will open to complete this step. Your input should match the resolution you just chose a few steps earlier. The Output should be equal to or greater than your Input (up to 1200 Pixels/Inch). Your Method should be 50% Threshold. If you are seeing Diffusion Dither (the default), click on the box to see other Method choices to find 50% Threshold. Choose OK. Your file is now in black and white in Bitmap mode.


Saving to Bitmap made my file size smaller, you say? Yes, it did, but it is still probably many MB large. Imagine having 4 or 5 of these files and organizing all this artwork into one large document. Your new art board can quickly get unwieldy and oversized.

Time to save your file as a TIFF (.tif file extension) and tap into the power of LZW! TIFF is the format of choice for commercial and professional image standards. TIFF is the most universal and most widely supported format across all platforms, Mac, Windows

5. To finish up, Select FILE > SAVE AS . The pop up window is looking for your file name and a format. Choose TIFF. Another window called TIFF Options will open. At the top (for Image Compression) select LZW and click OK.


Check your folder where you saved your TIFF The size is now probably under 1 MB. Your TIFF document was able to be compressed with all the quality you desire but now in a nicely managed little file.

Comparison of two files and their data size: one is a Photoshop (PSD) file at 3.6 MB and one is a TIFF file at 160KB because of LZW compression.

Important Numbers to Remember in Boxcar Platemaking 101

Everyday at Boxcar Press we throw around these numbers on the phone, in emails and to each other.  Some of us have even been known to mumble them in our sleep at night.  What makes them so special above all others?  See if you can guess what each one stands for.

94, 95, 145, 148, 152, 175: all of the plate types sold by Boxcar Press. The higher the number, the thicker the plate. 94 and 152 are available as both plastic backed and metal backed plates. If the number is followed by “SB”, it is a steel backed plate, not the number of stolen bases.

1:00: the time designated as the cut off or deadline for ordering same day rush service – 1:00pm EST to be exact.

6:00: the cut off time in the evening (again, Eastern standard time!) for creating a job ticket and submitting files for one day turnaround.

17 and 22: the largest plate size we can make in our platemakers that will fit on our Vandercook proofing press.  If your files measure greater than 17″ x 22″, break them up and submit 2 files.  You can always put them back together on your press to make letterpress love.

62 and 67: pricing per square inch for platemaking – $0.62/sq. inch for plates with the number 94 or 95 in their plate name; $0.67/sq. inch for plates with the number 145, 148, 152 and 175 in their plate name. And for some of you, ’67 may have meant the summer of love in San Francisco.

30: minimum charge for platemaking – $30 per job ticket.  Also the cost of overnight air shipping via UPS in the US.

.35 and .25: the minimum guaranteed line thickness for our plates measured in points (pt).  Lines should be .25pt for 94/95 plates and .35pt for anything larger.  Remember, dotted lines are considered dots and not lines.   Dots have their own special numbers and shouldn’t feel slighted at all.

1 and 1.25: preferred dot thickness for our plates, also measured in points.  Proper dot thickness helps those individual, stand-alone-by-themselves dots to stand firm and tall and press boldly into your paper.

0.5: the number in inches we add to your platemaking dimensions for the height and width.  This half inch is needed for the platemaking process.

.875 and .853: the thicknesses for the standard Boxcar base and the deep relief Boxcar base.  And some really good bowling scores after 3 games.

.918: this is an easy one. This refers to type high, or the standard height of type.  However, it also could refer to the Porsche 918 Spyder or the name of a letterpress club at the Lancaster Heritage Center Museum Print Shop in Lancaster, Pennsylvania (the 918 Club).

Now these numbers will have special significance for you too!