Chapter 2 - Operational Overview

2.0 Introduction

    The objective of this chapter is to present the essential information that you need to know in order to effectively use PhotoGrav. Section 2.1 briefly describes PhotoGrav's primary functions and flow of events that those functions support during a typical PhotoGrav session. Beginning with PhotoGrav version 3.0 multiple simultaneous PhotoGrav sessions can be opened, modified, and independently saved. Section 2.2 provides a concise, high-level description of the program's concepts and the rationale for those concepts. Finally, section 2.3 presents a list of items that summarize the important information about PhotoGrav.

2.1 Functional Flow of Events

    PhotoGrav employs a small number of primary toolbar buttons to functionally organize the major steps involved in engraving a photograph. Each functional button has one or more major functions to accomplish and, upon completion of those functions, control passes back to the main session window. Figure 2.1.1 illustrates the normal flow of events in PhotoGrav processing.



    The Open Image Button provides the capability to select the image that you want to engrave while the Select Material Button selects the engraving material that you want to use. PhotoGrav stores a set of processing parameters with each material that it models. These processing parameters are optimized for each particular material to ensure excellent engraving results without any user intervention. These optimized parameters make possible the “Final Process” path indicated in Fig 2.1-1.

    The Resize Image Button provides the capability for you to resize/resample the input image without having to rely on another software application to perform this task. PhotoGrav will NOT resize or even modify the original image in any way because PhotoGrav makes a working copy of the original file. Also, on every resize/resample operation PhotoGrav uses the original image to perform the resize operation in order to maintain the highest degree of quality.

    The Interactive Mode Button provides the capability to individually specify parameters for all of PhotoGrav’s processing functions and to view the result in near real time. Most importantly, one can view a simulation of what the engraving would actually look like on the material that you have selected. Although the Interactive Mode provides complete access to PhotoGrav’s functions that have been tuned specifically for Laser Engravers, you will probably find that you can seldom do better than PhotoGrav’s Automatic Final Processing option.

    The Final Process Button (Auto Process in previous versions) allows the input image to be processed and finalized in the proper format for the laser engraver. To ensure that the image is processed and finalized with the latest modifications of the parameters this operation should ALWAYS be performed whether in Interactive Mode or otherwise prior to saving the image to disk.

    The Viewing Panes (Figure 2.1.2), whether in split mode or otherwise, displays the Original (Input) image, the Grayscale image, the Engraved (Binary) image (the image that is to be used for engraving), and the Simulated image (what the engraving will look like on the selected material). The images appear on the screen one or two (if in split mode) at a time. One can, however, click a button to rapidly cycle through the various images for comparison purposes or view the images side by side when in split view mode. You can also magnify the images by clicking near the center of the area you want magnified or by defining a rectangular area to be enlarged to fill the screen. All three images are magnified by the same amount so comparisons are still easy to do even after magnification. Once the processed image is acceptable the various images can be save to disk for storing and to transfer to your engraver.

    The Save Image Button allows the various images (Original, Grayscale, Engraved, Simulated) to be saved to disk (when appropriate) in the supported file formats i.e. jpg, tif, bmp, png. When saving the Engraved image the jpg file format is NOT permitted due to the fact that in most cases it would ruin the engraved image information which would not be suitable for engraving.

2.2 Basic PhotoGrav Concepts

    The objective of the PhotoGrav program is to efficiently process digitized photographs so they can be engraved on a variety of common engraving materials with a high degree of confidence that the engraved photographs will be acceptable products. This objective is achieved via two basic PhotoGrav concepts:

1.     Processing operations that are "tuned" for each engraving material, and
2.     A simulation of the engraved image

    The intent of this section of the user guide is to provide a concise, high-level description of these two concepts and their underlying rationale. A more detailed description can be found in "Appendix 5: PhotoGrav Concepts and Design".

    PhotoGrav's processing operations were designed and developed specifically to process images for laser engraving and were parameterized so that a wide range of effects could be achieved by adjustment of the parameters. Then the parameters were individually "tuned" for each of the engraving materials supported by the program. This "tuning" was accomplished experimentally, using several test images, by specifying several sets of parameters for each engraving material, actually engraving the images on the material, and evaluating the resulting engravings. This process was repeated until the resultant engravings appeared to be near optimal for the subject material. The parameters that produced the final, "near optimal' engraving were then recorded and a data set was created for the material. These data sets are stored as part of the description of each engraving material and are automatically retrieved whenever a material is selected as the current engraving material within PhotoGrav.

    Although the tuning process described above results in "near optimal" parameter settings for each engraving material, engraving results are still often somewhat image dependent. In other words, the settings that produce an excellent engraving for one image on a specific material might result in an engraving that is less satisfactory for another image using the same engraving material. Further, it is very difficult to view the raw processed image on a computer monitor and to judge from that display whether or not the final engraving will be satisfactory. To overcome these difficulties, PhotoGrav provides, optionally, a simulation of what the processed image will look like once it is actually engraved on the selected material and the ability to modify the parameters as needed.

    PhotoGrav's simulation capability is intended to provide a WYSIWYG (What You See Is What You Get) capability. In other words, the appearance of the simulated image on your computer monitor should be close to the appearance of the actual engraving produced from the processed image for most of the included materials. The simulated image is not merely an overlay of "dots" on top of a representation of the engraving material, but rather a convolution of the various parameters and images.  In other words, it is a full-fledged simulation wherein a lens-power model, calibrated for each material, is used to calculate an effective laser spot size which is then "burned" into a representation of the engraving material. Further details about the simulation and model can be found in Appendix 5.

    The Simulation Image produced by PhotoGrav should always be a representation of the final engraving. For example, for "Black Laser Brass", the Simulation Image should appear with proper polarity even though the processed image, if displayed in its "raw" form, would appear to have a "negative" polarity. There is one special case of this WYSIWYG capability that should be noted. For acrylics, which are normally engraved on the "back" of the material, the Simulation Image produced by PhotoGrav is the view from the "front" of the material, i.e., the normal viewing perspective. So, even in this special case, the Simulation Image produced by PhotoGrav is a true WYSIWYG representation, i.e., the simulated engraving is presented as it would normally be viewed by your customers as a finished product. Although the primary utility of the Simulation Image is to help you make fine adjustments to create a more satisfactory engraving, it can also be printed and used for customer proofs or as supplements to file copies of your shop's projects. The prints are especially effective if you have a color printer attached to your computer.

    Although the simulation model has been calibrated for a variety of laser engravers and for many common engraving materials, there are bound to be variables that at times cause noticeable differences between PhotoGrav's Simulation Image and the actual engraving. For example, black laser brass from different manufacturers, or even different "batches" from the same manufacturer, will sometimes engrave somewhat differently under identical engraver settings. Also, variables in the laser engraver itself, e.g., dirty lenses or mirrors, can cause variations in the engraving performance. You should try to control these variables to the degree possible and also realize that PhotoGrav, like any other tool, requires some practice and skill on your part to adapt its capabilities to your particular environment and requirements. It is also important to remember that, for engraved photographs, "beauty is in the eye of the beholder", i.e., the perceived goodness of an engraving is a very subjective measure. You might therefore find that PhotoGrav's processing parameters for a particular material do not result in engravings that match your tastes. If so, use PhotoGrav's interactive processing capabilities (see Sec. 3.4) and its Named Parameter Sets to define things the way you want them to be.

    One other aspect of PhotoGrav's operational characteristics requires some discussion before concluding this section. In the Image Viewing Panes (see Fig. 2.1.2), PhotoGrav displays the Original Image, the Grayscale Image, the Engraved Image, and the Simulation Image for comparison purposes. The Grayscale Image is the input image and the Engraved Image is the processed binary image that is to be sent to the engraver. The Engraved Image is normally displayed in the same polarity and the same left-to-right orientation as the Grayscale Image even though those characteristics might be automatically changed by PhotoGrav when the image is saved on disk for transfer to your engraver. The reason for displaying the Engraved Image in this fashion is merely to facilitate the comparison to the input image. If this is a bit confusing, just remember that the Simulated Image always represents what will be engraved if you save the processed image (Engraved Image in PhotoGrav's terminology) to disk and transfer it to the engraver with no changes.

2.3 Important PhotoGrav Information

    The following is a collection of important things that you should know about PhotoGrav. Some of the items have already been discussed in previous sections and some of them will be covered in later sections. However, since much of the information following Chapter 2 is very detailed and is intended as reference material, the essential elements of that information are summarized below so you can begin using PhotoGrav with confidence after reading this section. If an item is discussed elsewhere in this document, then a reference to the appropriate section is included below.

1. PhotoGrav has been designed for compatibility with a display screen color pixel depth of 32-bit and a resolution of 1024 x 768 or larger. See section 1.2 of the PhotoGrav User Guide for instructions on how to adjust this. (Reference: Sec. 3.3)
    
2. The input image ("Original/Grayscale Image") for PhotoGrav can be any image type in the following format: tif, bmp, jpg, png. (Reference: Sec. 3.2.2)
    
3. The input image to PhotoGrav should be scanned in some image processing program such as CorelDraw or Adobe PhotoShop, so that its size and resolution (dpi) are "correct". If the image is already in a digital format then PhotoGrav is able to resample the image to the desired size and resolution (dpi). Most images taken with a digital camera have an arbitrary resolution of either 72 or 96 dpi. In most engraving cases a dpi of 72 or 96 must be altered for best results.
   
   The dpi (dots per inch) for the image should be the same, or an integer factor or divisor, of the dpi at which you intend to engrave the image. For example, if you intend to engrave at 250 or 500 dpi, then the image should be scanned at 250 dpi. If you intend to engrave at 300 or 600 dpi, then the image should be scanned at 300 dpi. Engraving results can often be very disappointing otherwise. The size of the image, at the scanned resolution (dpi), should be the desired size of the final engraved image.
    
4. Processed photographs (PhotoGrav's "Engraved Image") should be engraved using the highest resolution lens (smallest spot size) that you have available. If you do not own your manufacturer's "high-resolution lens" and if you intend to engrave a lot of photographs, then you might consider obtaining such a lens.
    
5. Use PhotoGrav's “Machine Properties” or “Select Machine” dialog window to set the parameters and characteristics for your specific laser engraver. The “Machine Properties” window is accessible from the File→System Defaults→Select Machine menu item. The session “Machine Properties” can be modified by selecting Session→Select Machine from the menu bar. (Reference: Sec. 3.6)
   
   Although you specified your Laser Engraver model and its maximum power on your very first PhotoGrav execution, there are other parameters that further define your specific machine. In particular, within the “Machine Properties” window, you should add and/or delete lenses from the “Lenses” list to match your set of lenses. Similarly, the list of “dpi's” should be edited to reflect the dpi settings available on your machine. Also, if your laser engraver’s maximum wattage is not listed under “Watts” then add it to the list as well.
    
6. PhotoGrav is not designed to "Print" directly to laser engravers. To engrave a PhotoGrav processed image (the "Engraved Image"), save the "Engraved Image" to disk and use your standard program, e.g., CorelDraw, to send the image to the engraver. (Reference: Sec. 4.1.2.1)
    
7. DO NOT RESIZE NOR ROTATE the "Engraved Image" (the image to be sent to the engraver) in CorelDraw, or any other image processing program, before sending it to your engraver. The "Engraved Image" is a binary image, as it must be for laser engraving, and resizing and rotation operations in general do not work well for binary images.
    
8. PhotoGrav's “Sessions” provide a powerful mechanism whereby you can customize PhotoGrav's parameters to achieve the results you want and can be assured that those results are repeatable in the future. If PhotoGrav's default parameter settings do not provide a satisfactory result for a specific material after the “Final Process” button is pressed, then select the “Interactive Mode” button to create "Engraved Images" at several parameter settings that you suspect might be better. Save the various “Session’s” with different names and then actually engrave the images. Choose the engraving you prefer and then delete the “Session’s” that do not correspond to that “best” engraving. If satisfied with the “best” engraving, note which session was used and/or rename it so you can readily access it in the future for similar engraving projects. Otherwise, repeat the process until the results are satisfactory. You can now use this “Session” as a template to begin other similar “Session” types. (Reference: Sec. 3.1)
    
9. The engraving material to be modeled is selected via the “Material Properties” dialog window. The “Material Properties” dialog window can be accessed by selecting the File→System Defaults→Select Material menu item. The session “Material Properties” can be modified by selecting Session→Select Material from the menu bar. (Reference: Sec. 3.2.3)
    
10. The leather materials included with PhotoGrav, unlike most of the other furnished engraving materials, are not standardized materials. Further, the engraving behavior of leather depends very much on the tanning process, whether the leather is oiled or not, etc. therefore, PhotoGrav's Simulation Image for any specific leather material might not be a good representation relative to the specific leather material that you want to use. However, you can use the furnished material as a starting point for your own calibration process wherein you save your final, calibrated parameters as a PhotoGrav Session File Template.
     
11. The list of engraving materials includes two plastic materials that are “User-Defined Caps” with white or black cores. These materials can be used to model just about any plastic with a solid-color cap and with either a black or white core. Some calibration and parameter adjustment, as described in item 8 above, might be necessary for certain plastics and colors. (Reference: Sec. A1.1, Tip 5)
     
12. Two copies of PhotoGrav cannot be running at the same time. If PhotoGrav refuses to start, there is probably another copy of PhotoGrav running in a minimized window.
     
13. PhotoGrav produces temporary image files during its execution that can become quite large if the input image is large. Try to maintain a reasonable quantity of free disk space on the hard disk where you installed PhotoGrav (200 MB should be more than adequate for most purposes).
     
14. PhotoGrav is a Windows 32-bit program which runs equally well under 2000, XP, and Vista. A 64-bit version is planned to be released and it is recommended that you call PhotoGrav or check online at www.photograv.com for the latest information.