• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
1 //---------------------------------------------------------------------------------
2 //
3 //  Little Color Management System
4 //  Copyright (c) 1998-2021 Marti Maria Saguer
5 //
6 // Permission is hereby granted, free of charge, to any person obtaining
7 // a copy of this software and associated documentation files (the "Software"),
8 // to deal in the Software without restriction, including without limitation
9 // the rights to use, copy, modify, merge, publish, distribute, sublicense,
10 // and/or sell copies of the Software, and to permit persons to whom the Software
11 // is furnished to do so, subject to the following conditions:
12 //
13 // The above copyright notice and this permission notice shall be included in
14 // all copies or substantial portions of the Software.
15 //
16 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
17 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO
18 // THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
19 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
20 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
21 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
22 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
23 //
24 //---------------------------------------------------------------------------------
25 //
26 
27 #include "lcms2_internal.h"
28 
29 
30 // Auxiliary: append a Lab identity after the given sequence of profiles
31 // and return the transform. Lab profile is closed, rest of profiles are kept open.
_cmsChain2Lab(cmsContext ContextID,cmsUInt32Number nProfiles,cmsUInt32Number InputFormat,cmsUInt32Number OutputFormat,const cmsUInt32Number Intents[],const cmsHPROFILE hProfiles[],const cmsBool BPC[],const cmsFloat64Number AdaptationStates[],cmsUInt32Number dwFlags)32 cmsHTRANSFORM _cmsChain2Lab(cmsContext            ContextID,
33                             cmsUInt32Number        nProfiles,
34                             cmsUInt32Number        InputFormat,
35                             cmsUInt32Number        OutputFormat,
36                             const cmsUInt32Number  Intents[],
37                             const cmsHPROFILE      hProfiles[],
38                             const cmsBool          BPC[],
39                             const cmsFloat64Number AdaptationStates[],
40                             cmsUInt32Number        dwFlags)
41 {
42     cmsHTRANSFORM xform;
43     cmsHPROFILE   hLab;
44     cmsHPROFILE   ProfileList[256];
45     cmsBool       BPCList[256];
46     cmsFloat64Number AdaptationList[256];
47     cmsUInt32Number IntentList[256];
48     cmsUInt32Number i;
49 
50     // This is a rather big number and there is no need of dynamic memory
51     // since we are adding a profile, 254 + 1 = 255 and this is the limit
52     if (nProfiles > 254) return NULL;
53 
54     // The output space
55     hLab = cmsCreateLab4ProfileTHR(ContextID, NULL);
56     if (hLab == NULL) return NULL;
57 
58     // Create a copy of parameters
59     for (i=0; i < nProfiles; i++) {
60 
61         ProfileList[i]    = hProfiles[i];
62         BPCList[i]        = BPC[i];
63         AdaptationList[i] = AdaptationStates[i];
64         IntentList[i]     = Intents[i];
65     }
66 
67     // Place Lab identity at chain's end.
68     ProfileList[nProfiles]    = hLab;
69     BPCList[nProfiles]        = 0;
70     AdaptationList[nProfiles] = 1.0;
71     IntentList[nProfiles]     = INTENT_RELATIVE_COLORIMETRIC;
72 
73     // Create the transform
74     xform = cmsCreateExtendedTransform(ContextID, nProfiles + 1, ProfileList,
75                                        BPCList,
76                                        IntentList,
77                                        AdaptationList,
78                                        NULL, 0,
79                                        InputFormat,
80                                        OutputFormat,
81                                        dwFlags);
82 
83     cmsCloseProfile(hLab);
84 
85     return xform;
86 }
87 
88 
89 // Compute K -> L* relationship. Flags may include black point compensation. In this case,
90 // the relationship is assumed from the profile with BPC to a black point zero.
91 static
ComputeKToLstar(cmsContext ContextID,cmsUInt32Number nPoints,cmsUInt32Number nProfiles,const cmsUInt32Number Intents[],const cmsHPROFILE hProfiles[],const cmsBool BPC[],const cmsFloat64Number AdaptationStates[],cmsUInt32Number dwFlags)92 cmsToneCurve* ComputeKToLstar(cmsContext            ContextID,
93                                cmsUInt32Number       nPoints,
94                                cmsUInt32Number       nProfiles,
95                                const cmsUInt32Number Intents[],
96                                const cmsHPROFILE     hProfiles[],
97                                const cmsBool         BPC[],
98                                const cmsFloat64Number AdaptationStates[],
99                                cmsUInt32Number dwFlags)
100 {
101     cmsToneCurve* out = NULL;
102     cmsUInt32Number i;
103     cmsHTRANSFORM xform;
104     cmsCIELab Lab;
105     cmsFloat32Number cmyk[4];
106     cmsFloat32Number* SampledPoints;
107 
108     xform = _cmsChain2Lab(ContextID, nProfiles, TYPE_CMYK_FLT, TYPE_Lab_DBL, Intents, hProfiles, BPC, AdaptationStates, dwFlags);
109     if (xform == NULL) return NULL;
110 
111     SampledPoints = (cmsFloat32Number*) _cmsCalloc(ContextID, nPoints, sizeof(cmsFloat32Number));
112     if (SampledPoints  == NULL) goto Error;
113 
114     for (i=0; i < nPoints; i++) {
115 
116         cmyk[0] = 0;
117         cmyk[1] = 0;
118         cmyk[2] = 0;
119         cmyk[3] = (cmsFloat32Number) ((i * 100.0) / (nPoints-1));
120 
121         cmsDoTransform(xform, cmyk, &Lab, 1);
122         SampledPoints[i]= (cmsFloat32Number) (1.0 - Lab.L / 100.0); // Negate K for easier operation
123     }
124 
125     out = cmsBuildTabulatedToneCurveFloat(ContextID, nPoints, SampledPoints);
126 
127 Error:
128 
129     cmsDeleteTransform(xform);
130     if (SampledPoints) _cmsFree(ContextID, SampledPoints);
131 
132     return out;
133 }
134 
135 
136 // Compute Black tone curve on a CMYK -> CMYK transform. This is done by
137 // using the proof direction on both profiles to find K->L* relationship
138 // then joining both curves. dwFlags may include black point compensation.
_cmsBuildKToneCurve(cmsContext ContextID,cmsUInt32Number nPoints,cmsUInt32Number nProfiles,const cmsUInt32Number Intents[],const cmsHPROFILE hProfiles[],const cmsBool BPC[],const cmsFloat64Number AdaptationStates[],cmsUInt32Number dwFlags)139 cmsToneCurve* _cmsBuildKToneCurve(cmsContext        ContextID,
140                                    cmsUInt32Number   nPoints,
141                                    cmsUInt32Number   nProfiles,
142                                    const cmsUInt32Number Intents[],
143                                    const cmsHPROFILE hProfiles[],
144                                    const cmsBool     BPC[],
145                                    const cmsFloat64Number AdaptationStates[],
146                                    cmsUInt32Number   dwFlags)
147 {
148     cmsToneCurve *in, *out, *KTone;
149 
150     // Make sure CMYK -> CMYK
151     if (cmsGetColorSpace(hProfiles[0]) != cmsSigCmykData ||
152         cmsGetColorSpace(hProfiles[nProfiles-1])!= cmsSigCmykData) return NULL;
153 
154 
155     // Make sure last is an output profile
156     if (cmsGetDeviceClass(hProfiles[nProfiles - 1]) != cmsSigOutputClass) return NULL;
157 
158     // Create individual curves. BPC works also as each K to L* is
159     // computed as a BPC to zero black point in case of L*
160     in  = ComputeKToLstar(ContextID, nPoints, nProfiles - 1, Intents, hProfiles, BPC, AdaptationStates, dwFlags);
161     if (in == NULL) return NULL;
162 
163     out = ComputeKToLstar(ContextID, nPoints, 1,
164                             Intents + (nProfiles - 1),
165                             &hProfiles [nProfiles - 1],
166                             BPC + (nProfiles - 1),
167                             AdaptationStates + (nProfiles - 1),
168                             dwFlags);
169     if (out == NULL) {
170         cmsFreeToneCurve(in);
171         return NULL;
172     }
173 
174     // Build the relationship. This effectively limits the maximum accuracy to 16 bits, but
175     // since this is used on black-preserving LUTs, we are not losing  accuracy in any case
176     KTone = cmsJoinToneCurve(ContextID, in, out, nPoints);
177 
178     // Get rid of components
179     cmsFreeToneCurve(in); cmsFreeToneCurve(out);
180 
181     // Something went wrong...
182     if (KTone == NULL) return NULL;
183 
184     // Make sure it is monotonic
185     if (!cmsIsToneCurveMonotonic(KTone)) {
186         cmsFreeToneCurve(KTone);
187         return NULL;
188     }
189 
190     return KTone;
191 }
192 
193 
194 // Gamut LUT Creation -----------------------------------------------------------------------------------------
195 
196 // Used by gamut & softproofing
197 
198 typedef struct {
199 
200     cmsHTRANSFORM hInput;               // From whatever input color space. 16 bits to DBL
201     cmsHTRANSFORM hForward, hReverse;   // Transforms going from Lab to colorant and back
202     cmsFloat64Number Threshold;         // The threshold after which is considered out of gamut
203 
204     } GAMUTCHAIN;
205 
206 // This sampler does compute gamut boundaries by comparing original
207 // values with a transform going back and forth. Values above ERR_THRESHOLD
208 // of maximum are considered out of gamut.
209 
210 #define ERR_THRESHOLD      5
211 
212 
213 static
GamutSampler(CMSREGISTER const cmsUInt16Number In[],CMSREGISTER cmsUInt16Number Out[],CMSREGISTER void * Cargo)214 int GamutSampler(CMSREGISTER const cmsUInt16Number In[], CMSREGISTER cmsUInt16Number Out[], CMSREGISTER void* Cargo)
215 {
216     GAMUTCHAIN*  t = (GAMUTCHAIN* ) Cargo;
217     cmsCIELab LabIn1, LabOut1;
218     cmsCIELab LabIn2, LabOut2;
219     cmsUInt16Number Proof[cmsMAXCHANNELS], Proof2[cmsMAXCHANNELS];
220     cmsFloat64Number dE1, dE2, ErrorRatio;
221 
222     // Assume in-gamut by default.
223     ErrorRatio = 1.0;
224 
225     // Convert input to Lab
226     cmsDoTransform(t -> hInput, In, &LabIn1, 1);
227 
228     // converts from PCS to colorant. This always
229     // does return in-gamut values,
230     cmsDoTransform(t -> hForward, &LabIn1, Proof, 1);
231 
232     // Now, do the inverse, from colorant to PCS.
233     cmsDoTransform(t -> hReverse, Proof, &LabOut1, 1);
234 
235     memmove(&LabIn2, &LabOut1, sizeof(cmsCIELab));
236 
237     // Try again, but this time taking Check as input
238     cmsDoTransform(t -> hForward, &LabOut1, Proof2, 1);
239     cmsDoTransform(t -> hReverse, Proof2, &LabOut2, 1);
240 
241     // Take difference of direct value
242     dE1 = cmsDeltaE(&LabIn1, &LabOut1);
243 
244     // Take difference of converted value
245     dE2 = cmsDeltaE(&LabIn2, &LabOut2);
246 
247 
248     // if dE1 is small and dE2 is small, value is likely to be in gamut
249     if (dE1 < t->Threshold && dE2 < t->Threshold)
250         Out[0] = 0;
251     else {
252 
253         // if dE1 is small and dE2 is big, undefined. Assume in gamut
254         if (dE1 < t->Threshold && dE2 > t->Threshold)
255             Out[0] = 0;
256         else
257             // dE1 is big and dE2 is small, clearly out of gamut
258             if (dE1 > t->Threshold && dE2 < t->Threshold)
259                 Out[0] = (cmsUInt16Number) _cmsQuickFloor((dE1 - t->Threshold) + .5);
260             else  {
261 
262                 // dE1 is big and dE2 is also big, could be due to perceptual mapping
263                 // so take error ratio
264                 if (dE2 == 0.0)
265                     ErrorRatio = dE1;
266                 else
267                     ErrorRatio = dE1 / dE2;
268 
269                 if (ErrorRatio > t->Threshold)
270                     Out[0] = (cmsUInt16Number)  _cmsQuickFloor((ErrorRatio - t->Threshold) + .5);
271                 else
272                     Out[0] = 0;
273             }
274     }
275 
276 
277     return TRUE;
278 }
279 
280 // Does compute a gamut LUT going back and forth across pcs -> relativ. colorimetric intent -> pcs
281 // the dE obtained is then annotated on the LUT. Values truly out of gamut are clipped to dE = 0xFFFE
282 // and values changed are supposed to be handled by any gamut remapping, so, are out of gamut as well.
283 //
284 // **WARNING: This algorithm does assume that gamut remapping algorithms does NOT move in-gamut colors,
285 // of course, many perceptual and saturation intents does not work in such way, but relativ. ones should.
286 
_cmsCreateGamutCheckPipeline(cmsContext ContextID,cmsHPROFILE hProfiles[],cmsBool BPC[],cmsUInt32Number Intents[],cmsFloat64Number AdaptationStates[],cmsUInt32Number nGamutPCSposition,cmsHPROFILE hGamut)287 cmsPipeline* _cmsCreateGamutCheckPipeline(cmsContext ContextID,
288                                           cmsHPROFILE hProfiles[],
289                                           cmsBool  BPC[],
290                                           cmsUInt32Number Intents[],
291                                           cmsFloat64Number AdaptationStates[],
292                                           cmsUInt32Number nGamutPCSposition,
293                                           cmsHPROFILE hGamut)
294 {
295     cmsHPROFILE hLab;
296     cmsPipeline* Gamut;
297     cmsStage* CLUT;
298     cmsUInt32Number dwFormat;
299     GAMUTCHAIN Chain;
300     cmsUInt32Number nGridpoints;
301     cmsInt32Number nChannels;
302     cmsColorSpaceSignature ColorSpace;
303     cmsUInt32Number i;
304     cmsHPROFILE ProfileList[256];
305     cmsBool     BPCList[256];
306     cmsFloat64Number AdaptationList[256];
307     cmsUInt32Number IntentList[256];
308 
309     memset(&Chain, 0, sizeof(GAMUTCHAIN));
310 
311 
312     if (nGamutPCSposition <= 0 || nGamutPCSposition > 255) {
313         cmsSignalError(ContextID, cmsERROR_RANGE, "Wrong position of PCS. 1..255 expected, %d found.", nGamutPCSposition);
314         return NULL;
315     }
316 
317     hLab = cmsCreateLab4ProfileTHR(ContextID, NULL);
318     if (hLab == NULL) return NULL;
319 
320 
321     // The figure of merit. On matrix-shaper profiles, should be almost zero as
322     // the conversion is pretty exact. On LUT based profiles, different resolutions
323     // of input and output CLUT may result in differences.
324 
325     if (cmsIsMatrixShaper(hGamut)) {
326 
327         Chain.Threshold = 1.0;
328     }
329     else {
330         Chain.Threshold = ERR_THRESHOLD;
331     }
332 
333 
334     // Create a copy of parameters
335     for (i=0; i < nGamutPCSposition; i++) {
336         ProfileList[i]    = hProfiles[i];
337         BPCList[i]        = BPC[i];
338         AdaptationList[i] = AdaptationStates[i];
339         IntentList[i]     = Intents[i];
340     }
341 
342     // Fill Lab identity
343     ProfileList[nGamutPCSposition] = hLab;
344     BPCList[nGamutPCSposition] = 0;
345     AdaptationList[nGamutPCSposition] = 1.0;
346     IntentList[nGamutPCSposition] = INTENT_RELATIVE_COLORIMETRIC;
347 
348 
349     ColorSpace  = cmsGetColorSpace(hGamut);
350     nChannels   = cmsChannelsOfColorSpace(ColorSpace);
351     nGridpoints = _cmsReasonableGridpointsByColorspace(ColorSpace, cmsFLAGS_HIGHRESPRECALC);
352     dwFormat    = (CHANNELS_SH(nChannels)|BYTES_SH(2));
353 
354     // 16 bits to Lab double
355     Chain.hInput = cmsCreateExtendedTransform(ContextID,
356         nGamutPCSposition + 1,
357         ProfileList,
358         BPCList,
359         IntentList,
360         AdaptationList,
361         NULL, 0,
362         dwFormat, TYPE_Lab_DBL,
363         cmsFLAGS_NOCACHE);
364 
365 
366     // Does create the forward step. Lab double to device
367     dwFormat    = (CHANNELS_SH(nChannels)|BYTES_SH(2));
368     Chain.hForward = cmsCreateTransformTHR(ContextID,
369         hLab, TYPE_Lab_DBL,
370         hGamut, dwFormat,
371         INTENT_RELATIVE_COLORIMETRIC,
372         cmsFLAGS_NOCACHE);
373 
374     // Does create the backwards step
375     Chain.hReverse = cmsCreateTransformTHR(ContextID, hGamut, dwFormat,
376         hLab, TYPE_Lab_DBL,
377         INTENT_RELATIVE_COLORIMETRIC,
378         cmsFLAGS_NOCACHE);
379 
380 
381     // All ok?
382     if (Chain.hInput && Chain.hForward && Chain.hReverse) {
383 
384         // Go on, try to compute gamut LUT from PCS. This consist on a single channel containing
385         // dE when doing a transform back and forth on the colorimetric intent.
386 
387         Gamut = cmsPipelineAlloc(ContextID, 3, 1);
388         if (Gamut != NULL) {
389 
390             CLUT = cmsStageAllocCLut16bit(ContextID, nGridpoints, nChannels, 1, NULL);
391             if (!cmsPipelineInsertStage(Gamut, cmsAT_BEGIN, CLUT)) {
392                 cmsPipelineFree(Gamut);
393                 Gamut = NULL;
394             }
395             else {
396                 cmsStageSampleCLut16bit(CLUT, GamutSampler, (void*) &Chain, 0);
397             }
398         }
399     }
400     else
401         Gamut = NULL;   // Didn't work...
402 
403     // Free all needed stuff.
404     if (Chain.hInput)   cmsDeleteTransform(Chain.hInput);
405     if (Chain.hForward) cmsDeleteTransform(Chain.hForward);
406     if (Chain.hReverse) cmsDeleteTransform(Chain.hReverse);
407     if (hLab) cmsCloseProfile(hLab);
408 
409     // And return computed hull
410     return Gamut;
411 }
412 
413 // Total Area Coverage estimation ----------------------------------------------------------------
414 
415 typedef struct {
416     cmsUInt32Number  nOutputChans;
417     cmsHTRANSFORM    hRoundTrip;
418     cmsFloat32Number MaxTAC;
419     cmsFloat32Number MaxInput[cmsMAXCHANNELS];
420 
421 } cmsTACestimator;
422 
423 
424 // This callback just accounts the maximum ink dropped in the given node. It does not populate any
425 // memory, as the destination table is NULL. Its only purpose it to know the global maximum.
426 static
EstimateTAC(CMSREGISTER const cmsUInt16Number In[],CMSREGISTER cmsUInt16Number Out[],CMSREGISTER void * Cargo)427 int EstimateTAC(CMSREGISTER const cmsUInt16Number In[], CMSREGISTER cmsUInt16Number Out[], CMSREGISTER void * Cargo)
428 {
429     cmsTACestimator* bp = (cmsTACestimator*) Cargo;
430     cmsFloat32Number RoundTrip[cmsMAXCHANNELS];
431     cmsUInt32Number i;
432     cmsFloat32Number Sum;
433 
434 
435     // Evaluate the xform
436     cmsDoTransform(bp->hRoundTrip, In, RoundTrip, 1);
437 
438     // All all amounts of ink
439     for (Sum=0, i=0; i < bp ->nOutputChans; i++)
440             Sum += RoundTrip[i];
441 
442     // If above maximum, keep track of input values
443     if (Sum > bp ->MaxTAC) {
444 
445             bp ->MaxTAC = Sum;
446 
447             for (i=0; i < bp ->nOutputChans; i++) {
448                 bp ->MaxInput[i] = In[i];
449             }
450     }
451 
452     return TRUE;
453 
454     cmsUNUSED_PARAMETER(Out);
455 }
456 
457 
458 // Detect Total area coverage of the profile
cmsDetectTAC(cmsHPROFILE hProfile)459 cmsFloat64Number CMSEXPORT cmsDetectTAC(cmsHPROFILE hProfile)
460 {
461     cmsTACestimator bp;
462     cmsUInt32Number dwFormatter;
463     cmsUInt32Number GridPoints[MAX_INPUT_DIMENSIONS];
464     cmsHPROFILE hLab;
465     cmsContext ContextID = cmsGetProfileContextID(hProfile);
466 
467     // TAC only works on output profiles
468     if (cmsGetDeviceClass(hProfile) != cmsSigOutputClass) {
469         return 0;
470     }
471 
472     // Create a fake formatter for result
473     dwFormatter = cmsFormatterForColorspaceOfProfile(hProfile, 4, TRUE);
474 
475     // Unsupported color space?
476     if (dwFormatter == 0) return 0;
477 
478     bp.nOutputChans = T_CHANNELS(dwFormatter);
479     bp.MaxTAC = 0;    // Initial TAC is 0
480 
481     //  for safety
482     if (bp.nOutputChans >= cmsMAXCHANNELS) return 0;
483 
484     hLab = cmsCreateLab4ProfileTHR(ContextID, NULL);
485     if (hLab == NULL) return 0;
486     // Setup a roundtrip on perceptual intent in output profile for TAC estimation
487     bp.hRoundTrip = cmsCreateTransformTHR(ContextID, hLab, TYPE_Lab_16,
488                                           hProfile, dwFormatter, INTENT_PERCEPTUAL, cmsFLAGS_NOOPTIMIZE|cmsFLAGS_NOCACHE);
489 
490     cmsCloseProfile(hLab);
491     if (bp.hRoundTrip == NULL) return 0;
492 
493     // For L* we only need black and white. For C* we need many points
494     GridPoints[0] = 6;
495     GridPoints[1] = 74;
496     GridPoints[2] = 74;
497 
498 
499     if (!cmsSliceSpace16(3, GridPoints, EstimateTAC, &bp)) {
500         bp.MaxTAC = 0;
501     }
502 
503     cmsDeleteTransform(bp.hRoundTrip);
504 
505     // Results in %
506     return bp.MaxTAC;
507 }
508 
509 
510 // Carefully,  clamp on CIELab space.
511 
cmsDesaturateLab(cmsCIELab * Lab,double amax,double amin,double bmax,double bmin)512 cmsBool CMSEXPORT cmsDesaturateLab(cmsCIELab* Lab,
513                                    double amax, double amin,
514                                    double bmax, double bmin)
515 {
516 
517     // Whole Luma surface to zero
518 
519     if (Lab -> L < 0) {
520 
521         Lab-> L = Lab->a = Lab-> b = 0.0;
522         return FALSE;
523     }
524 
525     // Clamp white, DISCARD HIGHLIGHTS. This is done
526     // in such way because icc spec doesn't allow the
527     // use of L>100 as a highlight means.
528 
529     if (Lab->L > 100)
530         Lab -> L = 100;
531 
532     // Check out gamut prism, on a, b faces
533 
534     if (Lab -> a < amin || Lab->a > amax||
535         Lab -> b < bmin || Lab->b > bmax) {
536 
537             cmsCIELCh LCh;
538             double h, slope;
539 
540             // Falls outside a, b limits. Transports to LCh space,
541             // and then do the clipping
542 
543 
544             if (Lab -> a == 0.0) { // Is hue exactly 90?
545 
546                 // atan will not work, so clamp here
547                 Lab -> b = Lab->b < 0 ? bmin : bmax;
548                 return TRUE;
549             }
550 
551             cmsLab2LCh(&LCh, Lab);
552 
553             slope = Lab -> b / Lab -> a;
554             h = LCh.h;
555 
556             // There are 4 zones
557 
558             if ((h >= 0. && h < 45.) ||
559                 (h >= 315 && h <= 360.)) {
560 
561                     // clip by amax
562                     Lab -> a = amax;
563                     Lab -> b = amax * slope;
564             }
565             else
566                 if (h >= 45. && h < 135.)
567                 {
568                     // clip by bmax
569                     Lab -> b = bmax;
570                     Lab -> a = bmax / slope;
571                 }
572                 else
573                     if (h >= 135. && h < 225.) {
574                         // clip by amin
575                         Lab -> a = amin;
576                         Lab -> b = amin * slope;
577 
578                     }
579                     else
580                         if (h >= 225. && h < 315.) {
581                             // clip by bmin
582                             Lab -> b = bmin;
583                             Lab -> a = bmin / slope;
584                         }
585                         else  {
586                             cmsSignalError(0, cmsERROR_RANGE, "Invalid angle");
587                             return FALSE;
588                         }
589 
590     }
591 
592     return TRUE;
593 }
594 
595 // Detect whatever a given ICC profile works in linear (gamma 1.0) space
596 // Actually, doing that "well" is quite hard, since every component may behave completely different.
597 // Since the true point of this function is to detect suitable optimizations, I am imposing some requirements
598 // that simplifies things: only RGB, and only profiles that can got in both directions.
599 // The algorithm obtains Y from a syntetical gray R=G=B. Then least squares fitting is used to estimate gamma.
600 // For gamma close to 1.0, RGB is linear. On profiles not supported, -1 is returned.
601 
cmsDetectRGBProfileGamma(cmsHPROFILE hProfile,cmsFloat64Number threshold)602 cmsFloat64Number CMSEXPORT cmsDetectRGBProfileGamma(cmsHPROFILE hProfile, cmsFloat64Number threshold)
603 {
604     cmsContext ContextID;
605     cmsHPROFILE hXYZ;
606     cmsHTRANSFORM xform;
607     cmsToneCurve* Y_curve;
608     cmsUInt16Number rgb[256][3];
609     cmsCIEXYZ XYZ[256];
610     cmsFloat32Number Y_normalized[256];
611     cmsFloat64Number gamma;
612     cmsProfileClassSignature cl;
613     int i;
614 
615     if (cmsGetColorSpace(hProfile) != cmsSigRgbData)
616         return -1;
617 
618     cl = cmsGetDeviceClass(hProfile);
619     if (cl != cmsSigInputClass && cl != cmsSigDisplayClass &&
620         cl != cmsSigOutputClass && cl != cmsSigColorSpaceClass)
621         return -1;
622 
623     ContextID = cmsGetProfileContextID(hProfile);
624     hXYZ = cmsCreateXYZProfileTHR(ContextID);
625     if (hXYZ == NULL)
626         return -1;
627     xform = cmsCreateTransformTHR(ContextID, hProfile, TYPE_RGB_16, hXYZ, TYPE_XYZ_DBL,
628                                     INTENT_RELATIVE_COLORIMETRIC, cmsFLAGS_NOOPTIMIZE);
629 
630     if (xform == NULL) { // If not RGB or forward direction is not supported, regret with the previous error
631 
632         cmsCloseProfile(hXYZ);
633         return -1;
634     }
635 
636     for (i = 0; i < 256; i++) {
637         rgb[i][0] = rgb[i][1] = rgb[i][2] = FROM_8_TO_16(i);
638     }
639 
640     cmsDoTransform(xform, rgb, XYZ, 256);
641 
642     cmsDeleteTransform(xform);
643     cmsCloseProfile(hXYZ);
644 
645     for (i = 0; i < 256; i++) {
646         Y_normalized[i] = (cmsFloat32Number) XYZ[i].Y;
647     }
648 
649     Y_curve = cmsBuildTabulatedToneCurveFloat(ContextID, 256, Y_normalized);
650     if (Y_curve == NULL)
651         return -1;
652 
653     gamma = cmsEstimateGamma(Y_curve, threshold);
654 
655     cmsFreeToneCurve(Y_curve);
656 
657     return gamma;
658 }
659 
660