Chapter 3 - PhotoGrav Application

PhotoGrav 3.0

3.0 Introduction

    Chapter Two described PhotoGrav’s operational overview and how PhotoGrav uses these to provide a smooth flow of events within a PhotoGrav Session. This chapter, Chapter Three, provides a detailed description of each of those primary functional blocks as well as describing a PhotoGrav Session and the essentials of the PhotoGrav Application. The description with appropriate graphics include: (1) PhotoGrav Sessions, (2) The Primary Toolbar and its operations, (3) Viewing Panes and Panels, (4) Interactive Mode, (5) Cloning—Comparison of Results, (6) Machine Selection, and (7) Automatic Updates. It is especially recommended to become familiar with these primary functional blocks located on the Primary Toolbar and the respective operations since these are vital in producing a digital image for laser engraving.

3.1 PhotoGrav Sessions

    One of PhotoGrav’s primary design concepts is the notion of a “PhotoGrav Session” and its respective “Session File” (*.pgs). A “Session File” is a file that is designed to save the current state of ones work including all parameter settings, user preferences, machine and material info, as well as the source image. By permitting the source image to be saved with the session alleviates the need to remember where the “original” image file is located. One can simply reopen the “Session File” and perform any necessary modifications and/or adjustments without having to relocate the original image. The machine information will be stored in the “Session File” which is helpful, for example, if PhotoGrav is used with multiple engravers. This permits one to save machine/material “templates” such that the user can just open up the session “template” pertaining to that particular machine/material and begin using PhotoGrav with the machine and material info already selected and defined.

    Whenever an image is opened, PhotoGrav will automatically insert that image into either a new session OR an existing active session. Either way there will always be only one image associated with a PhotoGrav Session.

    Due to the “Session File” format, however, one must keep in mind that there are two modes of selecting a machine and/or material. These two modes are selecting the “Session” machine/material (Figure 3.1.1) and setting the “system” material/machine (Figure 3.1.2). The “Session” selection stays with that particular session and the “System Default” selection sets the default material/machine type so that any new session that is created will default to the machine/material type that is selected in the “System Default” settings.

    Session files can be very useful when becoming proficient with PhotoGrav in the following ways; when working with a difficult image, if multiple engraving machines are used, when working with multiple concurrent jobs, and in many other cases as well. PhotoGrav allows multiple session files to be opened simultaneously and offers some functions specifically related to Session files such as Cloning (Figure 3.1.3). For further instruction on cloning refer to Section 3.5 on Cloning—Comparison of Results .

    PhotoGrav has the capability to email Session files for easier review. For example PhotoGrav Session Files can be emailed to PhotoGrav Technical Support or to another office location for review simply by clicking on the Session→Email Session… menu item (Fig 3.1.4).

    From this point forward the majority of this section is in the context of a “PhotoGrav Session” file (.pgs files).


3.2 Primary Toolbar

3.2.1 Overview

    PhotoGrav is designed for simplicity, therefore, all of the primary functions necessary to prepare an image for laser engraving are grouped together and displayed in the “Primary Toolbar” (Fig 3.2.1). The Primary Toolbar provides quick access to the most commonly used functions.

Fig. 3.2.1: Primary Toolbar

    The Primary Toolbar has 5 basic functions that perform the minimum requirement operations to successfully laser engrave an image or photograph. As noted in Section 2.1 of this manual these 5 minimal steps are as follows:

  1. Open an Image (Input Image).
  2. Select the engraving material.
  3. Resize the image to the desired size.
  4. Process the image.
  5. Save the image to disk.

3.2.2 Open Image 

    The Open Image button simply displays a dialog window that allows an image in any PhotoGrav supported file type (bmp, jpg, tif, png) to be opened and inserted into either a new or existing session window. While the open file dialog filters the listed items to only show PhotoGrav supported image types. If the “All files (*.*)” option is selected any PhotoGrav file type can be opened such as PhotoGrav Session Files (pgs), PhotoGrav Parameter Files (prm, pgp), or PhotoGrav Supported Image Files (bmp, jpg, tif, png).

    The image that is initially opened is considered the “Original Image”. The image can be either color or grayscale. PhotoGrav then automatically converts the original image if necessary to a “Grayscale Image”. PhotoGrav considers the grayscale image because it is often much more reliable to compare the grayscale image (rather than the color image) to the engraved image.

3.2.3 Select Material 

    The “Select Material” button displays a dialog window listing all the available materials sorted by the various categories (see Fig 3.2.2). Remember that this material selection only changes the material for the “active” session. Refer to Section 3.1, Fig 3.1.2 to see how to change the default material setting. This list will be altered by the “Auto Update” feature (see Section 3.7) as more materials become available for download. PhotoGrav does not permit the user to modify this list due to the fact that many materials individually and specifically tested and fine tuned for the best results. While some material parameters are modifiable by the user there are a number of parameters that are fixed during the design and testing phase of that material. The material can also be chosen by double-clicking an item in the list or by highlighting the material and clicking the “OK” button. The selected material will then be displayed in the status bar at the bottom of the main application window.

    The Modify Material Color dialog window (Fig. 3.2.3) can only be invoked from the Select Material dialog window and provides the capability to the appearance of an engraving material. The capability to modify the engraving material’s appearance enhances PhotoGrav’s usefulness in two ways. The more important of the two ways is that it allows a broad range of solid-color plastics to be effectively modeled by PhotoGrav. This is achieved by providing two materials both of which have a User-Defined Cap but one of which has a white core and the other has a black core. These user-defined caps can be modified to have any solid color as will be described below. The other way that the capability to modify the engraving material’s appearance can be useful results from the fact that many engraving materials, although similar to those provided by PhotoGrav, might differ somewhat in color and brightness. The capability to alter their appearance might improve the fidelity of the simulated engravings produced by PhotoGrav.

    The material to be modified can be chosen by clicking a material item in the list in Fig. 3.2.2 and then clicking the “Modify” button. Pressing the “Modify” button causes the Modify Material dialog window to appear.

    The controls in the “Color Adjustments” frame are used to modify the appearance of the engraving material. The “Brightness” and “Contrast” controls affect the overall brightness and contrast of the material for all colors equally. The “Brightness” modification can range from -100 to +100 and the “Contrast” modification can range from -1.00 To + 1.00. The modification values can be changed only by clicking the scrollbars, not by direct numerical entries in the textboxes.

    The “Red Tint”, “Green Tint”, and “Blue Tint” scrollbars change the contrast of the respective colors. The tint modifications can range from -1.00 to +1.00 and can be changed only by clicking the scrollbars, not by direct numerical entries in the text boxes.

    Modifications caused by the adjustments are immediately visible in the material image view window. The “Reset” command button resets all of the scroll bars to the “no adjustment” state since the last time this material was modified. The “Reset to Default” button resets the adjustments to the default setting of the material, in other words to the settings of the material when originally shipped.

    As an example try selecting the “User-Defined Cap/White Core” material type under plastics. And click “Modify”. Then adjust the “Green Tint” and “Blue Tint” slider bars so that both have a value of -1.00. Note that the effect of these values is that the material image view window turns from white to bright red. That red color could be further adjusted by changes in the “Brightness”, “Contrast”, and “Red Tint” scroll bars. The net result is that one can create almost any desired color for the cap of a solid-color plastic for which the core color can be either white (in the example) or black.

3.2.4 Resize/Resample Image

     Resizing and/or Resampling the original input image (Fig 3.2.4) is almost always a requirement because one rarely receives the image in the actual size needed for engraving (this does vary some depending on the engravers policies). PhotoGrav offers the ability to resize/resample an image to the desired size without having to depend on other outside methods. PhotoGrav will raise a notification if it detects a discrepancy between the selected machine resolution (dpi) and the resolution (dpi) of the image. The image should be resampled to the same resolution (or an integer multiple of) as the desired engraving resolution (machine dpi setting). PhotoGrav uses the machine settings extensively to prepare and simulate the image to give the user an idea, estimate, or relative difference of what to expect when the actual engraving is performed. Therefore, PhotoGrav does not adjust the “actual engraver” setting, which is usually modified through the software driver that comes with the engraver, but rather only adjusts the “machine setting” in PhotoGrav which is then used to prepare the image for engraving.

3.2.5 Final Process 

    The “Final Process” command button performs the actual processing necessary to produce an image ready for the laser engraver. This button should be pressed in every case prior to saving the image to disk. Once the “Final Process” button is clicked PhotoGrav will process the image using the current parameter settings. After the processing is complete PhotoGrav will switch the image viewing pane to either the “Engraved” image or the “Simulated” image determined by which image is selected in the viewing pane toolbar (see Section 3.3, Fig 3.3.2). There will now be a total of three or four images to use for comparison purposes in order to further fine tune the results if needed.

3.2.6 Save Image 

    Now that the material has been selected and the image has been opened, resized, and processed it is ready to be saved to disk for engraving (Fig 3.2.5). To do this simply select the “Save Images” button on the Primary Toolbar and save the appropriate images to disk in any of the PhotoGrav supported file formats. The only exception is the “Engraved” image which cannot be saved as a jpeg due to the fact this format usually uses a lossy compression type scheme which would create dire effects on the engraved image. One can elect to save the images while flipping either horizontally, vertically or both. One may find the “Flip Horizontal” check box to be turned on depending on the material type selected due to the fact that some material types such as acrylic engrave better on the back side, therefore requiring the image to be flipped or mirrored. This can be altered, however, by modifying the parameters when in Interactive Mode and then saving the session as a Template Session.

    After the "Save Images" dialog is opened one must select the “Exit” button to close out of this dialog screen. The reason for this is that often it may be desirable to save more than just the “Engraved” image so this goes into a continuous loop until all images are saved as needed.

3.2.7 Display Info 

    The remaining buttons on the Primary Toolbar have to do with the way information is handled and viewed (see Fig 3.2.6). After pressing the “Display Info” button the “PhotoGrav Session Report” window will be displayed (Fig 1.6.1). This is a formatted report, that can be viewed or printed, of the parameter, machine, and image settings for a particular session. This report also includes thumbnail images of the original and simulated image types. This provides an opportunity to print and file every job performed while having quick access to all the data that was used for that job. One can also use it to quickly view all the relevant settings for a session in a neatly organized fashion. The PhotoGrav Session Report is also where an estimate of the engraving time can be located and any comments that might be helpful relating to the active session.

Fig. 3.2.6: Primary Toolbar

3.2.8 Size to Fit

    The “Size to Fit” button zooms all the images to fit within the viewing panes (see Section 3.3 for further information on Viewing Panes and Panels).

3.2.9 Split Window

    The “Split Window” button toggles between viewing the images in a single or double viewing mode (see Section 3.3 for further information on Viewing Panes and Panels).

3.3 Viewing Panes and Panels

    PhotoGrav provides a few options for displaying information about the image, session, machine, parameter, etc. The session window is divided up into 2 primary views. The first is the “Image” view. This is where the images are displayed and image commands such as zoom in, zoom out, pan, etc. are performed. Due to the numerous sizes and resolutions of existing monitors PhotoGrav offers the ability to view the images in either single or “split window” mode. This allows for a larger viewing area where the images can be cycled one at a time in single view mode or individually selectable by pressing the corresponding toolbar button. On the other hand it also permits one to compare side-by-side the resulting images in split screen mode (Fig 3.3.1).

    The second view that provides information is called the “Panel” view. The “Panel” view is further divided into two subsequent views named “Image Info” and “Parameter Info” (Fig 3.3.1). The “Image Info” panel (Fig 3.3.2) shows basic information about the image and the currently selected machine. The next sub panel is the “Parameter Info” panel (Fig 3.3.3) which displays a fixed summary of the current parameter settings. This “Parameter Info” view changes to permit adjustments and modifications to the parameters when in “Interactive Mode” which is discussed in Section 3.4.

    These panel views can be hidden to again provide for larger viewing areas as needed by selecting the appropriate toolbar button from the PhotoGrav Session Toolbar (Fig 3.3.4).

    There are four images that one can select for viewing namely Original input, Grayscale, Engraved/binary, and the Simulated images (Fig 3.3.5). If one has “Split Screen” selected then these images can be selected independently per image view. To open an image one can select the “Open Image” button on the primary command bar. This button can be selected even if there is no session window open in which case a new session window will be created and the respective image inserted into that session. If, on the other hand, an existing session is open then the selected image will be inserted over the existing image if an image exists. In other words, if the user already has a session open then he or she should create a “New” session prior to opening the image to prevent the replacement of the existing session’s image.

    By left or right clicking of the mouse button in either one of the two Image View Windows one can incrementally zoom in or out respectively. It is also possible to drag a zoom “box” or rectangle around the desired area for closer inspection of the images. Another image command is the “pan” command. This command centers the image at the point where the mouse button was clicked. Holding down the [Space Bar] will activate this command (Fig 3.3.6).

3.4 Interactive Mode

    The Interactive Mode Button toggles between two modes of operation. When in "Interactive Mode" the Interactive Mode Button will show a green “i” icon indicating that PhotoGrav is in "Interactive Mode". Similarly when PhotoGrav is NOT in “Interactive Mode” the button will display a red “i”.

    The “Interactive Mode” is designed for the primary purpose of providing a quick and efficient preview of the final image, since with average size images it would simply take too long to run through the entire PhotoGrav processing pipeline every time a small change is made to a parameter. With this in mind PhotoGrav distinguishes between “Preview” and “Final Process”. The “Final Process” button (formerly called “Auto Process” in previous versions) takes the raw image data along with the current material, parameter, and machine settings and completely processes the image producing the binary or engraved image ready to be saved and engraved. On the other hand the “Preview” buttons (only available in “Interactive Mode” - Fig 3.4.2) process a scaled version of the image (NOT THE ORIGINAL IMAGE) suitable for rapid viewing as one adjusts and modifies the parameters in almost if not real time.

    PhotoGrav does not restrict the image view display size therefore providing a larger viewing area for a more accurate representation of the resulting image. A larger viewing area does require more processing speed in order to maintain real time performance. The real time performance of interactively adjusting the parameter settings is a direct correlation to the size of the image and the size of the display screens viewing area. Since PhotoGrav permits arbitrary screen sizes it is better prepared to adapt to the increasing speeds of modern computers. Assuming 17” to 24” computer monitors and current average to high end computers one can expect almost real time performance when interacting with the parameters while in “Interactive Mode”.

    Due to the plethora of monitor and display types, resolutions, and sizes that exist in the market place today PhotoGrav offers a couple of options to facilitate the advanced user who relies on the “Interactive Mode” in their production cycle. The first option is the “Auto Preview” checkbox (Fig 3.4.2). This is provided to give the user the ability to regenerate the preview image automatically after each parameter adjustment without the user having to manually click on the “Preview” buttons. The user may select to turn this on or off depending on the image size and/or display screen size to increase performance. The second option is the “Progress Bar On” checkbox (Fig 3.4.2). This checkbox offers the user the option of increasing performance by turning this off. When the progress bar is turned off PhotoGrav will process the “Preview” image slightly faster, however, with larger images and depending on the speed of the users’ computer one may want to turn this on. By turning this on it gives a “heads up” as to what PhotoGrav is doing followed by an indication when the “Preview” image is ready for display.

    Once the image and parameters are determined either in “Interactive Mode” or otherwise then the user can select the “Final Process” button to process the image. Clicking on the “Final Process” button inherently assumes that the user is now ready to prepare and process the image for engraving and exporting. Once the final processing is complete one can export/save the images or compare the images to other sessions (see Section 3.5 on Cloning—Comparison of Results later on).

    While working in “Interactive Mode” the user may want to restore the parameters to a previous value. PhotoGrav provides parameter restoration at 3 different levels (Fig 3.4.3). The first is “Restore” which restores the parameter settings of the current session to the values it carried along the last time that the image was processed using the “Final Process” button. The second method of restoration is “Reset To System”. This resets the parameters to the default settings of the base material selected for that session. And finally the third level of restoring the parameters is “Reset To Last Saved”. When one clicks this button it resets the parameters back to the settings since the PhotoGrav Session was last saved.

    It may be desirable to export or import (Fig 3.4.3) some parameter settings while in Interactive Mode” and therefore PhotoGrav offers these capabilities through the selection of the respective buttons. PhotoGrav allows the user to import parameter settings from version 2.xx (.prm files) or version 3.xx and later (.pgp files), however, one can only export parameter settings in version 3.xx and above “pgp” format. The parameters can also be exported or imported via the menu bar at the top of the PhotoGrav Application Window.

    The remaining comments in this section describe the various parameter settings and the respective controls. PhotoGrav has five major processing functions whereby it transforms the original input image into the Engraved and Simulated images. All processing function can be toggled on or off by clicking on the small green or red lights beside each processing function turning the functions on or off respectively. Furthermore, all processing functions can be quickly reset by pressing the small blue “Reset” arrow beside each control function.

3.4.1 Adjust Grayshade

    Figure 3.4.4 displays a histogram, or distribution, of the gray shades in the Original (input) image. The horizontal axis ranges from zero (black) on the left to 255 (white) on the right. The height of the distribution indicates the relative number of image elements (pixels) that have the gray shade indicated by the corresponding point on the horizontal axis. (If a distribution is very “peaked” at certain gray shades, then the peaks are truncated and other heights scaled to prevent the peaks from totally dominating the distribution). As an example, for the distribution displayed in Fig. 3.4.4, there are many more values of “white” in the image compared to any other gray shade producing a large spike at the very far right of the histogram. The rest of the histogram looks to have a higher concentration of values near the middle of the gray shaded spectrum.

    The left (black) and right (red) triangles below the horizontal axis specify the black and white clipping values, respectively, for the “Adjust Grayshade” function, i.e., all grayshades to the left of the left triangle are set to black (zero) and all grayshades to the right of the right triangle are set to white (255) and the grayshades between are linearly scaled. The “Black” and “White” labels to the left of the distribution specify quantitatively the black and white clipping values (45 and 255, respectively, for the distribution in Fig. 3.4.4). The clipping values can be changed by “clicking and dragging” the triangles. As a result, the “Black” and/or “White” quantitative values will change and the effect will show up as a change in the Processed and simulated Image. The clipping values can also, of course, be reset by clicking the small blue “Reset” arrow. (Note: All the engraving materials delivered with PhotoGrav calculate the “1%” clipping values for the grayshade distribution).

    The middle (yellow) triangle below the horizontal axis is the “gamma” for the gray shade transfer function. Changing the gamma value, by clicking and dragging the triangle, has the effect of simultaneously changing the brightness and contrast of the image. Moving the triangle to the right will generally make the Processed Image brighter and moving it to the left will generally make it darker.

    The blue triangle (Fig 3.4.5) that slides in the vertical direction located on the left side of the histogram provides a scaling function so that a few values do not dominate the graph. Note that in Figure 3.4.5 the histogram shows a much more evenly distributed display thus far more readable. Both Figure 3.4.4 and Figure 3.4.5 are the exact same histogram but note how the two blue vertical triangles have different locations. By adjusting this vertical scaling triangle a much more readable view of the image distribution is achieved.

3.4.2 Enhance Edges

    The “Enhance Edges” function provides the capability to both “smooth” the image and to enhance the image’s edges. As with the “Adjust Grayshade” function, if the green “On” button is checked, then the function affects the image data; otherwise, if unchecked (red), there is NO effect regardless of the parameter settings.

    The “Extent” parameter pictured in Fig. 3.4.6 can be modified by entering a value directly in the appropriate textbox (contains “9” in Fig. 3.4.6) or by clicking the associated horizontal scrollbar. The "Extent" parameter specifies the relative size of the area around each pixel which is then smoothed. Small values indicate relatively little smoothing whereas large values specify relatively large smoothing.

    The “Strength” parameter specifies the degree to which edges are enhanced or emphasized . The “Strength” parameter is controlled in a manner similar to the “Extent” parameter except that its values range from -100% to +100% rather than 0% to 100%. Almost all of the useful settings for theStrength” parameter are positive but interesting effects can sometimes be achieved with negative settings.

    Although PhotoGrav automatically sets parameter values appropriate to each engraving material, it is a good idea for you to experiment with the “Extent” and “Strength” parameter settings to get a feel for their effect which at times can be rather dramatic. An interesting way to do this is to have the “Simulation” ON and to turn the “Enhance Edges” function alternately ON and OFF to observe the effect.

3.4.3 Apply Screen

    The “Apply Screen” function (Fig. 3.4.7) provides the capability to “screen” the image in preparation for thresholding which follows this function.

    The “Apply Screen” function actually performs a Diffusion Dithering. Diffusion Dithering is a technique to convert a grayshade image to a binary image (black & white only, no shades of gray) wherein the shades of gray in the original image are represented in the processed binary image by differing densities of black and/or white dots. Diffusion Dithering accomplishes this by converting each gray shade in the original image to either a black or white value depending on its value relative to a predetermined “threshold” value. The error in making this assignment is then “diffused” to neighboring pixels which eventually are also thresholded (and then error diffused) and so forth and so on throughout the entire image.

    The Diffusion Dithering within PhotoGrav has been designed and optimized specifically for laser engraving and is controlled by the two parameters indicated in Fig. 3.4.7: (1) ED Density and (2) Noise Gain. (The ED stands for Error Diffusion). The “ED Density” parameter can be used to darken lighter areas of the processed image without substantially affecting areas that are already dark and, vice versa, can be used to lighten darker areas of the image without substantially affecting areas that are already light. The “Noise Gain” parameter can be used to add noise to the image to reduce “contouring”, "repetitive pattern", or “jpeg artifacts” effects that often occur when grayshade images are converted to binary images.

    Both parameter values can be modified by clicking the scroll bars or by entering numeric values in the white text boxes directly above each scroll bar. Relative values for the “ED Density” parameter range from -100 (darken) to +100 (lighten). Relative values for the “Noise Gain” parameter range from 0% (no noise) to 100% (maximum noise).

3.4.4 Apply Threshold

    The “Apply Threshold” function (Fig 3.4.8) linearly combines the last two control functions (Enhance and Screen), pixel by pixel and with variable weights, before thresholding the result to create an “Engraver-ready” binary image.

    There are two parameters associated with the “Threshold” function: (1) the “Screen %” and (2) the “Output Threshold Level”. The first parameter, the “Screen %”, specifies how the two inputs to the function are combined by specifying the weighting factor assigned to the input from the “Screen” function. The weighting factor assigned to the image coming from the “Enhance” function is then equal to (100 - Screen %) . A value of zero for this parameter specifies that the resulting data, before thresholding, is totally from the “Enhance” function. A value of “100” for this parameter specifies that the data, before thresholding, is totally from the “Screen” function. A value of “50” for this parameter specifies that the two inputs are equally weighted and then combined. The “combine” portion of the “Threshold” function is always ON, i.e., the two inputs are ALWAYS combined, before thresholding, using the weighting factors specified by the “Screen %” factor.

    The second parameter, the “Threshold Level”, specifies a threshold value which ranges from zero to 255. The threshold value is applied to the combined output of the “Enhance” and “Screen” functions, weighted as described above. If a combined value is less than the threshold value, then it is assigned a zero (black). If a combined value is greater than the threshold value, then it is assigned a one (white). The “threshold” portion of this function, unlike the “combine” portion, can be turned ON or OFF by checking, or not checking, the green/red checkbox located to the left of the label “Threshold Level”. If the thresholding is OFF, then the simulation function, described in the next section, cannot be turned ON and an engraver-ready (binary) image is not produced.

    Either parameter for this function can be modified by clicking the horizontal scroll bars or by entering a numeric value in the white text boxes immediately below the scroll bars.

3.4.5 Speed and Power

    The vertical scroll bars labeled “Power” and “Speed” (Fig 3.4.9) specify the percentage of maximum power and the percentage of the maximum speed for the laser engraver currently being modeled (You can change the laser engraver being modeled as well as the specifications for any laser engraver by selecting a different machine see Section 3.6). The “Power” and “Speed” controls should be very similar to the controls which actually exist on your laser engraver and should behave in the same fashion.

    The “Maximize Power” and “Maximize Speed” (Fig 3.4.9) checkboxes determine whether the Power setting or Speed setting for your machine is maximized when it is necessary to modify these settings. The necessity for modifying these settings occurs since PhotoGrav’s engraving materials were calibrated using a specific machine; therefore the power, speed, resolution, etc. of your machine may not match those of the “calibration” machine. PhotoGrav strives to deliver the appropriate quantity of energy to each laser spot, based on the settings for your machine, and in so doing has a choice of what values to use for the Power and Speed settings (generally a large number of settings will all satisfy the energy requirement). If you are interested in engraving as fast as possible, then the “Maximize Speed” box should be checked. If you are more comfortable with a higher Power setting, then the “Maximize Power” box should be checked. These two boxes cannot both be checked or unchecked at the same time so the boxes also act as toggles, i.e., if you check the “Maximize Power” box, then the “Maximize Speed” box will automatically become unchecked and vice versa. (Note: The effect of these checkboxes may at times appear confusing and it may at first appear to you that they are not working properly. It is important to remember that “Maximize” is used for both boxes to mean the maximum value for that parameter that will still result in the proper energy being delivered to the laser spot and that maximum value may not be 100%. For example, if the “Maximize Speed” box is checked, then it would be possible for the Power and Speed settings to be, e.g., 100% and 65%, respectively, which might at first seem incorrect since “Speed” was to have been maximized. However, in the example given, if the Speed is more than 65%, then inadequate energy will be delivered to the laser spot since the Power setting cannot be more than 100% (Speeding the engraver up delivers less energy to each spot). So, in this case, 65% is indeed the “maximum” value for the Speed setting subject to the constraint that the proper quantity of energy is delivered to the laser spot).

3.4.6 Other Parameters

    The remaining parameter settings and various other functions are located under the “Other Parameters” group box.

    The text box labeled “Machine DPI”, containing the value 300 in Fig 3.4.10, specifies the Engraver resolution, NOT the image resolution, in dots per inch. The value in this textbox is initially taken from the dpi value selected from the “Machine Preferences” dialog box.  It should be noted that when changing the “Machine DPI” will only cause the DPI setting to become the Engraver resolution for the current session. The textbox labeled “Image DPI” is for reference only and thus cannot be altered by the user.

    The “Reverse Polarity” checkbox provides the capability to set the polarity of the Engraved and Simulation images. Positive polarity materials are those for which the laser, when on, causes the engraving material to become darker, e.g., most woods. Negative polarity materials are those for which the laser, when on, causes the engraving material to become lighter, e.g., black laser brass and acrylics. The “Mirror Image” checkbox provides the capability to “mirror-the-image” (flip left to right) the Engraved and Simulation images. This feature is useful for materials like acrylic which are engraved on the “back” of the engraving material but viewed from the front. For various reasons the processed image is not shown “mirrored” in the Image Viewing Windows, but rather the Engraved and Simulated images are flipped (by user selection) only when written to disk.

    A few other options are also available such as turning the Simulation on or off as well as exporting or importing parameters either from the current or previous versions of PhotoGrav. Refer to the beginning of this Section (3.4) for further information on most of these settings and functions.

    See Section 2.2 for a more complete discussion of the underlying rationale for the simulation capability and how it can be an extraordinarily useful tool.

3.5 Cloning—Comparison of Results

    The comparison of images whether simulated or otherwise can be an efficient time saving procedure when it comes to preparing the image for engraving. PhotoGrav offers two different methods by which one can compare the processed image. The first is to compare the various images solely within a particular session (Fig 3.5.1) and second is to compare the results of two sessions with each other (Fig 3.5.2).

    Learning how to use the “Cloning—Image Comparison” features along with the simulation of results should again increase productivity. While the simulation is attempting to get as close as possible to the final results there are many variables that affect the results of the actual vs. the simulated images. Therefore, the simulation can be thought of as a relative comparison of the simulated images rather than an absolute final result. This essentially means that once one learns how a particular “simulated” image compares to the actual engraved image for a specific material and machine type; then a “relative” difference or pattern should emerge giving the user a sense of how to adjust the parameters to improve the actual engraving. This simulation feature was significantly relied on during the design of PhotoGrav to improve performance and efficiency.

    PhotoGrav has a “Clone” function (Fig 3.5.2) to further assist in comparing processed results. This “Clone” feature assumes that the user wants to spin off or clone another session based on the current active session. This provides an exact duplicate of the current selected session or active session. This provides an efficient method to quickly process another session and compare the two (if desired) without having to go through the whole process of reopening the same image in another session. For example, it can be helpful to compare one simulated or engraved image (session X), where the parameters have been adjusted, with a second image (session Y) where the parameters have NOT been modified (i.e. default material settings).

3.6 Machine Properties

    The “Machine Properties” dialog window (Fig. 3.6.1) can only be invoked from the main application menu bar and is used to select and modify the laser engraver and associated parameters which PhotoGrav is currently modeling. The “Machine Make” frame provides the capability for you to select your laser engraver manufacturer and model type. The “Machine Properties”, “Machine Resolution”, “Machine Lens Spot Size”, and “Machine Watts” frames provide the capability for you to modify, add to, or specify completely, the parameters that essentially define the laser engraver model.

    The list at the top of the “Machine Model” frame displays the laser engraver machines currently modeled by PhotoGrav including a “User Defined Laser” machine for which you can completely specify the engraver parameters from scratch. Each machine manufacturer in the list also provides a “Generic” laser model type in the case where the specific model type is not known but the manufacturer is known. In the case of the “Generic” model type all the machine properties can be defined just as in the “User Defined Laser” case.

    Selecting a machine from the list will enter the machine’s name into the text box directly to the right of the list along with the machine model type. It will also change all the settings to reflect which machine type is selected.

    Clicking the “Reset to Default” button will restore a machine’s parameters, to the values they had when PhotoGrav was first installed, for whatever machine is currently selected. Any machine’s parameters can be modified using the controls in the “Machine Properties” dialog window and, once the “OK” button is pressed, the modified parameters become the current parameters for the machine and are stored to disk as such when the current PhotoGrav session terminates).

    The first two textboxes at the top of the “Machine Properties” frame specify the maximum power (in watts) and the maximum speed (in inches/second) for the current laser engraver. These two values obviously have a big influence on how PhotoGrav produces the Simulated Image. The third textbox from the top specifies the time, in seconds, for the laser to slow down, stop, and reverse direction for each scan line. This parameter is used only for calculating estimates of the engraving time, which are displayed in the PhotoGrav Session Report (see Section 3.2.7). A procedure for calculating this parameter for your particular machine is presented in Appendix 3: Calculational Procedure for “Turn Time”.

    The list displayed in the “Machine Lens Spot Size” frame contains a list of the effective laser spot sizes (diameters in inches) for the lenses available to the simulated Laser Engraver. These are the values that are available to PhotoGrav for creating the Simulated Image. A single click of an item in the list only locally selects the item. When an item in the property listbox is selected two functions can be performed, namely “Del” or “Use”. The “Del” button deletes the item from the list while the “Use” button places that value into the associated text under the “Machine Properties” frame. Double clicking on a list item will behave just as if the “Use” button was pressed. Also, values in the list textbox can be Added to the list by clicking the “Add” button.

    PhotoGrav adjusts itself appropriately so that the simulated engraving is as realistic as possible. The lens that is installed on the laser engraver is the lens that should be specified in this textbox. Generally, for photographs, the spot size corresponding to the highest-resolution is the best lens to use, if that lens is available for your machine.

    The second list is the “Machine Resolution” frame which contains a list of the resolutions (dots per inch) available to the simulated Laser Engraver. The controls in this frame behave identically to the controls in the “Machine Lens Spot Size” frame as described in the paragraph above. Similarly, the “Machine Watts” frame behaves just as the other two similar frames.

    It is important to remember that there are two locations where the “Machine Properties” can be selected. The first one is located under the File→System Defaults→Select Machine… menu item (Fig 3.6.2). When this option is selected ONLY THE DEFAULT MACHINE TYPE IS CHOSEN which means that any new session that is created will use this machine type. The second method of opening the “Machine Properties” dialog window is located in the Session→Select Machine… menu item (Fig 3.6.3). When this method is used ONLY THE ACTIVE SESSION MACHINE PROPERTIES ARE MODIFIED.

3.7 Automatic Updates

    Another feature that can be very useful in PhotoGrav is the ability for additional materials and machine types (when available) to be added automatically via an internet connection on any computer that has PhotoGrav installed (Fig 3.7.1). This does not prevent one from still saving/exporting and loading/importing parameter files and PhotoGrav Sessions (pgp files) for both current and previous versions of PhotoGrav and custom configuring the machine settings as required.

    The available method to check for updates is through the Help menu item as shown in Figure 3.7.1. There are three main items that PhotoGrav checks for when performing a “Check for Update” function. The first and second are to check for any new Materials and Machines. The third is to check for any updates to the application. If any one of these three checks indicates a need to update then a message listing the current vs. latest versions available (Fig 3.7.2) appears. The updates can then be selected to “Yes” go ahead and download or “No” just leave it as it is.