Product Review – ChromaPure Releases a Winner
If you’re a Videophile, you’re already aware of the importance of a good display calibration, and you may have invested the time and money into doing the job yourself. If you have done the calibration yourself, you may have come to the realization that many calibration programs are written by programmers rather than calibrators and these programs can be hard to work with or missing in key features. For these reasons, I was very interested in hearing the news that Tom Huffman was releasing his own calibration software. Tom is well known and respected in the AVS Forum and video calibration communities and he has authored some key posts at AVS Forum (including this must read on Color Management Systems). Being an experienced calibrator, Tom knows what he wants to see in calibration software and after using the product to calibrate several different displays, I’m happy to report that Tom has accomplished what he has set out to do. ChromaPure is an excellent video calibration tool and as we will see, it has some key features that sets it apart from the competition.
Before getting into the nitty gritty calibration details, let’s talk about the key feature set of the program. (Also please note that v1.1 of the software was released just as this article was being completed and the features of this version will be discussed towards the end of this article).
- Very nice and easy to use CMS calibration menu with separate % error indicators for HS and L for all RGBCYM primaries and secondaries. Each color also displays the color difference (dE) between the selected standard and the measured value. This feature alone makes the program a standout. If a full blown CMS is not available, the program also has a nice color decoding menu as a rough way to optimize the gamut with the tint/color controls.
- Use of color difference (dE) error indications throughout the measurement menus (greyscale, gamut, etc.), which makes it easy to decide when it’s safe to stop tweaking or when more calibration time is necessary.
- User selectable color difference conventions (CIELUV, CIELAB or CIE94).
- User selectable colorspace choices (Rec.709, SMPTE-C, EBU, DCI).
- Meter offset feature, which makes it very easy to train one meter from another. This can also be used to calibrate directly from the projector while compensating for room and diffuser effects (first measure the projector off of the screen without the diffuser and use this offset information while performing subsequent measurements directly off the projector).
- The program supports the following probe types: X-Rite Display 2 Colorimeter, X-Rite Chroma 5 Colorimeter and X-Rite i1Pro SpectroPhotometer
- Optimized Workflow - Leave it up to an experienced calibrator like Tom to get the calibration steps ordered correctly.
- Very intuitive and easy to use GUI - The calibration steps are ordered from top to bottom with each step represented by an icon that activates a menu tab.
- All of the standard calibration metrics are well supported (White Point, Greyscale tracking, and Gamma).
- Very detailed and comprehensive context sensitive help menus.
The ChromaPure software can be purchased separately or sold as a bundle with several different probe types. Installing ChromaPure is a breeze and it’s possible to install it on multiple computers so long as the same probe is used. Unlike other programs, ChromaPure does not lock the meter in order to prevent its use in other programs. If you buy a meter as a bundle with ChromaPure, you’re free to use it with other programs and if you use a meter that isn’t bundled with ChromaPure, it will work fine so long as the software can read the serial number on the probe so that ChromaPure can be licensed properly.
So how does the software perform?
After installing the software and hooking it up to an X-Rite Chroma 5 Colorimeter, the first thing that was readily apparent is the maturity and stability of the instrumentation interface. With one minor exception that I’ll talk about later, the probe readings were very solid, consistent, reproducible and there were no issues at all with the probe interface. As a first release of the software, I expected the probe to behave similar to other programs that I’ve used in the past which is to say a little flaky. Instead the probe interface is rock solid.
The other thing that is readily apparent is the well thought out and easy to use workflow. The software layout is perfect for the typical calibration. If one goes through the menus from the topmost icon buttons (pre-calibration steps) through the middle icons (calibration steps) to the bottom (post-calibration steps), the results will work very well. As a case in point - one display that I calibrated was a JVC RS20, which offers a very good CMS (with v1.1 of the JVC firmware), the RS20 also has an 11-step greyscale adjustment where both the greyscale and the gamma can be adjusted. The greyscale is adjusted using separate R, G and B settings while the gamma is adjusted using the white (RGB) setting. The ChromaPure work-flow defaults to setting the gamma first, followed by the greyscale color balance and I think this makes much more sense than the other way around (because the gamma adjustment is usually a more coarse adjustment while the greyscale is more of a fine tuning adjustment). Doing it in this fashion helps to minimize the amount of time spent doing unnecessary calibration, although a person is free to move the calibration steps around in a different order if they wish.
So let’s take a close look and examine the menus along the way.
The Option menu is not too unusual with the exception that it provides support for various dE models and another nicety that allows the user to select the number of measurements and report either the Mean (average) or Median. Here is a link that describes the differences between the two and it’s easy to see why I prefer the Median method if the readings are not consistent and there are some outliers in the data set. In actual practice the measurements with a C-5 were consistent so both methods delivered about the same results.
The offset menu is shown below and as previously mentioned this is a nice feature that allows someone to automatically keep and maintain an offset between two different probes. This is particularly useful when one probe is not very accurate but has better dark performance, in this case the less accurate meter can be “trained” by the more accurate meter with a bright test pattern and then used for dark, low IRE measurements. I also found it very useful as away to correct for diffuser, screen and room color errors. In this situation the same meter (C-5) was measured off the screen without a diffuser (as the reference meter), the diffuser was then added and while using the same test pattern a second reading was done at the projector (as the field meter). I noticed a 5 dE (CIE94) color error from just the diffuser alone being added (both measurements off of the screen), so you can see why it’s important to factor out these contributions to color error.
Next up is the pre-calibration Grayscale adjustment (see below) which tells us what to fix and where. This also gives us a baseline for the final improvements to gamma and greyscale. As can be seen from the screenshot below, the overall menu layout is excellent and it’s a nice touch that the gamma and greyscale RGB balance are all presented on the same screen.
The Color Gamut is also measured as part of the Pre-Calibration steps. As can be seen the x,y locations of RGBCYMW are displayed relative to the chosen colorspace (Rec. 709, EBU, etc.). The RGBCYM luminance information is also shown which is a critical component that is often left off of other calibration menus when measuring the gamut. The color difference dE for each primary and secondary is also shown.
Now we can move on to the actual calibration. The White Point menu is shown below. (Side note: The user should be careful to ensure that the Y reading is well above the minimum sensitivity of the probe and Chromapure includes a Y reading for this purpose, something that was added at my request early in the Chromapure development phase). Note that the measurement smoothing settings that we saw earlier in the options menu are repeated here as an override for this particular menu. If the user has a display where the gain and offset settings are buried in the service menu, this is the time when they need to make those adjustments to get the coarse D65 color temp adjusted before final tuning with the greyscale and gamma adjustments.
The Color Decoding menu was skipped because the display being used (JVC RS20) uses a CMS which is the more precise and therefore preferred way to set the color gamut. The CMS menu is shown below. The separate indicators of Hue, Saturation and Lightness along with the dE for each color makes using the CMS a breeze. This feature is a blessing for anyone with a display that has a CMS and one of the standout features of ChromaPure. Note that the colors are designed to be worked through in the order seen in the menu (top to bottom, left to right) and the color selection automatically advances. Once a color has been measured it’s possible to go back and redo it, but other than that the order must be followed. I would have preferred to go through the colors in any order (based on the sequence of test patterns being used) and I’ve communicated this desire to Tom, so hopefully this will be added in a future release. Tom has mentioned that test patterns are available for free that follow the order being used in the program so that is another option as well.
After getting the gamut dialed in, the gamma adjustment comes next. The continuous measurement option makes setting the gamma a very quick operation that yielded very accurate results. The menu below shows the results after adjusting for a gamma of 2.2. This also shows one weakness in the initial release which is support for only 9 data points along the greyscale. Supporting the 5% grey point is very important in getting shadow detail correct and lack of an adjustment point in this region is a shortcoming. After discussing this with Tom, I was pleased to see that support for a gamma adjustment in this region was made a priority in v1.1 and it is currently available. Some devices including the JVC RS20 also include support for a 95% gamma adjustment and I would like to see this added in future releases (along with support for 20 greyscale steps at 5% increments across the full greyscale).
After the main calibration steps have been completed, it’s time to measure the greyscale again. This is the same step as was done previously, if everything is okay a user can advance to the next step. If there are still issues (color or gamma), it’s possible to go back and touch up one or more regions. As is usually the case with calibration, all settings tend to be related so that modifications in one area will make changes elsewhere and the post calibration measurements are needed in order in order to determine if one is done or if more work is needed (lather, rinse, repeat).
Next up is the color gamut measurement again. This step is needed in order to determine where the xyY points ended up at for our primaries and secondaries. If the greyscale, gamma and color gamut all measured well during post calibration then we are done, except for saving our data and generating a report. Otherwise, if something has shifted during the adjustment phase it’s time to go back and do another iteration.
The report generation uses Microsoft Excel which provided the only real snag that I encountered with the product. The laptop that I use for calibration has Open Office Calc loaded rather than Excel and the report generation is incompatible with calc. For now if you use ChromaPure you’ll want to have Excel already loaded. Tom has said that later versions of the product will incorporate custom plotting and reporting software so that Excel is not needed. The reports that are generated are excellent however and I’ve included a sample file in .pdf format. It’s worth mentioning that there is a workaround if Excel is not load, simply export the data, copy it to a machine with ChromaPure AND Excel installed and then import the data and then press the calibration report icon.
Here is a sample report generated in PDF Format that was taken from an actual calibration of a JVC RS20 that was used for this article. As you can see it’s possible to obtain excellent results from ChromaPure and if the display has a full greyscale and CMS adjustment as the JVC has, ChromaPure is an essential tool.
The only real issue that I had when running ChromaPure happened while I was training a QA engineer on calibrating a 50″ Panasonic Plasma and had to go back and forth between menu’s and measurements while explaining how the calibration process works. As mentioned, ChromaPure allows the calibrator to freely move back and forth across the menu’s in an ad-hoc fashion and apparently I had taken some measurements with the continuous mode enabled in in one menu and then attempted another measurement in another menu while the continuous mode was still enabled. Subsequent measurements in the new menu caused the software operation to lag and eventually become unstable and crash. I reported this to Tom and it was fixed with the release of v1.1. Other than that the program worked exceptionally well.
As previously mentioned, one other feature that I would like to see added is measurement support for all 5% greyscale steps which can provide a better perspective on greyscale accuracy, particularly if the greyscale has sharp spikes and dips. Most displays do not provide calibration points with this degree of precision which is why it was left out of ChromaPure, but measuring the greyscale with this degree of precision even if one can’t directly modify the greyscale is still useful. This is particularly true if there are greyscale spikes or dips that are so pronounced that a person may be willing to tradeoff accuracy in the adjacent 10% steps (or full greyscale if 10% adjustments are not available). In conversations with Tom, full 5% support is targeted for the 2.0 release so this feature should be available soon, in the meantime the program is very useful as is.
Another feature that I would like to see added is color and greyscale measurements that are completely random access. The program auto advances in a prescribed order and allows the user to go back and redo steps, but initially the program forces the calibrator to go through the colors in a prescribed fashion as the later steps/colors are grayed out. It seems easy enough for the software to support auto advance while also allowing the user to jump ahead to whatever color/greyscale step that they want to start with.
New V1.1 features
As mentioned, a new version of the program was released after the initial cut of this review was completed. The new version added some important new features including:
- Support for DTP-94 colorimeter
- Support for CIE2000 color difference model
- XML support for session exports.
- Handling of situations where continuous mode is enabled in one menu and a single measurement is attempted in another menu.
Tom says that many more features are planned for later releases including:
- Calibration automation by building support for external signal generators.
- Support for additional high-end meters.
- Dropping the Excel reporting entirely and adding integrated reporting with pdf output (you mention this in the review).
Tom says that he hopes to have these features implemented before the end of the year. He also hopes to release Version 2 with new modules and a richer feature set in the first or second quarter of 2010.
I asked Tom what his key goals were when he set off to develop ChromaPure. He said that he wanted to offer a calibration program that incorporated the features that he wanted to use, along with a well thought out workflow. I’m pleased to report that ChromaPure has delivered on those goals and more. ChromaPure is an excellent calibration program that is well worth the very reasonable $200 purchase price. The software is easy to use, well thought out and is very stable. Surprisingly so for an early release. The CMS support is a standout feature that is not available in competing products and by itself is worth the price of the software. When combined with all of the other features like multiple colorspace support and multiple color difference model support, the program is a compelling bargain. I found that the program yielded excellent results while significantly speeding up my calibration times. After using the program, I’ve decided to use ChromaPure for all of my display calibration needs. Future display reviews on this blog will be done using ChromaPure, so expect the graphs from ChromaPure to show up often.