Hi Jayathirth,Thank you for attaching the detailed logs, but I don't have a program that can deal with the 7z files. Can you summarize what was learned from them?
Also, the colormap you created, while subset, was a perfectly scaled cube. I was referring more to a random colormap where you might have 2 colors close to a primary, but neither is on a line from the primary to the 0.5 gray value so each has a different hue. That's something that can only be evaluated visually. One example of randomized colormaps is when we display via X11 onto an 8-bit display. That probably never happens any more, but we may not be able to allocate colors in the colormap in such a case and if another program has already allocated most of the dynamic colormap then we would not be able to add our own colors.
This could be dealt with by simply marking our standard colormap as having primaries, or by scanning any given colormap and marking it if it has primaries, and then only perform this code on colormaps with the primaries. Solving it for our own colormap (or solving it for any colormap that has all primaries) would likely solve it for 99% of the vanishingly small number of developers who might run into this.
But, in the end, what would we accomplish by adding this one very targeted fix?
I'm also curious where the push for this is coming from. While we aren't perfect here, so much of the world today is focused on lossless image formats that I don't imagine there is much need for really good 8-bit indexed image support any more...?
If anything, spatial dithering is considered a very low quality algorithm and error propagation dithering would handle all of the colormaps much better. We used to do error propagation dithering back in the JDK 1.1 days, but we dropped it when we introduced 2D because we added a bunch of ways to render small pieces of an image and only the current spatial dithering algorithm can be started in the middle of an operation. That doesn't mean that you can't still do error propagation since many operations already operate on the full image any way and you can still handle subset image operations by either converting the full image first and then copying or by tracing the errors from the edge of the image to the point of the subimage operation. We never bothered to upgrade our algorithms it just never seemed to be work that made sense to prioritize given that screens were overwhelmingly moving to full-color at the time of "Java 2" (and now to HDR in 2016+). 8-bit indexed isn't used much any more.
If we want to make 8-bit destination images work better we'd be better off adopting error propagation dithering again rather than trying to tune this algorithm for black.
It looks like the bug was closed briefly in 2014 and then reopened soon thereafter with no justification. It is true that we still have this anomaly, but it isn't clear why this is high enough priority to work on in 2016 when other bit depths would work better for destination imagery and other dithering algorithms would work better for most customers and even this targeted fix isn't perfect...
...jim
On 2/16/2016 8:32 AM, Jayathirth D V wrote:
Hi Jim, Thanks for letting me know about the importance of custom color maps. I was not able to understand what you mentioned previously since I am new to this terminology. Regarding performance I checked with image having complete 255,255,128 pixels and ran it for 100 times. I am running on Windows 7 Professional SP1 with Intel i5-5300U CPU. Overall I don't see much difference in time taken for drawImage() API before and after change. Details for INT_RGB image as input: Before change : Minimum time 536827ns Maximum time 1560947ns Average time 871167ns After change : Minimum time 536380ns Maximum time 1468130ns Average time 830778ns There is +/- 10% delta both for before and after change time but there is no major gap. Even for image with other input type it holds the same. Regarding custom color maps, previously I ran on default color map generated in TYPE_BYTE_INDEXED constructor. Now I tested with modified color map so that it doesn't contain any of the primary color values. Instead of using 0-255 values with value 51 increments in R,G,B components I used color map with 20-245 values with value 45 as increment. For this color map before and after change all the pixels are referring to same index in color map irrespective of removal of error delta addition in case of primary colors. I have attached log for Red and Green primary colors before and after change(Was not able to attach for more since it exceeded 120KB mailing list limit). Please search for "Final index value =" in the logs. Please let me know your inputs. Thanks, Jay -----Original Message----- From: Jim Graham Sent: Tuesday, February 16, 2016 1:03 AM To: Jayathirth D V Cc: 2d-dev@openjdk.java.net; Philip Race; Prasanta Sadhukhan Subject: Re: [OpenJDK 2D-Dev] Review Request for JDK-7116979 : Unexpected pixel colour when converting images to TYPE_BYTE_INDEXED Hi Jayathirth, The issue with testing performance with white images is that the tests allow the code to eliminate 3 indexed fetches which take time. Primary colors end up being the one obscure case where the new code might be faster. But, non-primary colors would be slower by a fair amount, so performance testing with converting a randomized or non-primary-color image are the more telling case. An image filled with 255,255,128 would be the worst case because it would involve all of the tests and still have to do all of the lookups. My question about how this works with custom colormaps was not really addressed by your response. A simple test to make sure the colormap has accurate (or very close) conversions for the primary colors may be enough to validate the colormap for the indicated tests. If the colormap contains no pure conversions for some of the primary colors then they may need to be dithered anyway... ...jim On 2/15/16 3:39 AM, Jayathirth D V wrote:Hi Jim, I performed performance analysis with white image so that all conditions are checked in the new branch added. There is no major difference in time taken before and after change. For each input I have tested time taken for drawImage() API to convert from every format to Byte indexed type. For every unique conversion test is run for 100 times. Please find the details: Input type Min before change (ns) Min after change (ns) Max before change (ns) Max after change (ns) Average before change (ns) Average after change (ns) INT_RGB 523437 481491 1230724 1270440 789452 666144 INT_ARGB 500232 493986 12406307 1308816 793384 654015 INT_ARGB_PRE 500233 492201 1037057 981277 710250 699214 INT_BGR 537716 562706 1446703 2046001 862377 863256 3BYTE_BGR 483275 481045 1181638 1384676 651427 580961 4BYTE_ABGR 544410 499786 1292305 968783 690106 683881 4BYTE_ABGR_PRE 504249 505588 1680086 1216445 756101 687750 USHORT_565_RGB 507818 505588 978153 1346746 652908 655782 USHORT_555_RGB 510496 509604 952272 1162004 650418 670811 BYTE_GRAY 481491 478367 1140585 1799231 691160 583250 USHORT_GRAY 506927 507373 1375751 1255267 728202 646902 BYTE_BINARY 541733 496217 1083466 959411 730527 728461 The changes are tested with plain images having primary colors like RED, GREEN, BLUE, BLACK and WHITE. Thanks, Jay -----Original Message----- From: Jim Graham Sent: Friday, February 12, 2016 4:05 AM To: Jayathirth D V; 2d-dev@openjdk.java.net; Philip Race; Prasanta Sadhukhan Subject: Re: [OpenJDK 2D-Dev] Review Request for JDK-7116979 : Unexpected pixel colour when converting images to TYPE_BYTE_INDEXED Hi Jayathirth, Did you do any performance analysis of this change? You are adding 6 tests and multiple branches to per-pixel code. The effectiveness of this technique depends on the colormap that we have set up. For the BufferedImage.TYPE_INDEXED constructor we produce a fairly nice colormap, but if someone creates a custom colormap then the colors could be anything. We create a decent inversion for just about any colormap, but that doesn't mean that using only "the best match for solid red" will produce a better result for a dithered approximation for red. It is true that if there is a really good match for red then we should just use that, but if there are no direct matches for red then we may choose to paint a red region with solid orange even though there is another color in the colormap that when mixed with orange approximates a red tone better. For example, if a colormap contains no pure red, but contains: 240, 20, 0 240, 0, 20 (I'm not sure if 20 is within our current error deltas that we use for dithering, but this is an example not a test case.) Then using one of these alone might skew the color towards orange or purple. Using both together in a dither pattern might keep the overall hue impression as red, but with a small amount of noise in its saturation. What types of colormaps was this tested with? ...jim On 2/11/16 6:37 AM, Jayathirth D V wrote:Hi,_Please review the following fix in JDK9:___Bug :https://bugs.openjdk.java.net/browse/JDK-7116979Webrev :http://cr.openjdk.java.net/~jdv/7116979/webrev.00/Issue : When Image containing black pixels are converted from anyformat to Byte Indexed format some of the pixels are not black. Theyare following pattern similar to dithering.Root cause : When we convert any format type to ByteIndexed we areadding Error delta values to R,G,B components using dithering indices.This is causing some pixels values to not point to proper index incolor table.Solution : There is no need to add error delta for primary colorscontaining basic values in R,G,B components. Exclude such pixels fromdelta addition.Thanks,Jay
