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* Modern Brightness/Contrast: Photoshop's brightness curve The modern brightness curve was a line rolled off by a v^P term. It sat up to 4 levels off Photoshop's in the highlights, and up to 2.3 levels off for lowered brightness. The curve is refit to the Photoshop ground truth we have: - the ±50 samples from 4759d12b; - the photoshop corpus's brightness +25 / contrast +30 files, inverted through the (exact) contrast curve. Raised, it is the line s*x (s = 1.375^(b/50)) up to a knee at 80/255, then a cubic Hermite to white with end slope s^-6.6. Lowered, it is the exact inverse of the curve raised by as much (the -50 samples confirm this to within a level). Every measured point is within about a level. For strong values the knee moves down so the curve stays monotone across -150..150. Brightness then contrast are evaluated through one 4096-entry table, built in 55 us. The GPU uses that same table through the Levels/Curves kernel instead of rebuilding the curves in WGSL, so GPU and CPU agree by construction. Photoshop oracles: rgb8/16/32 and gray8/16/32 brightness-contrast now pass (145 -> 151 of 258). The floor goes 133 -> 151. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * CMYK: Brightness/Contrast curves each ink, as Photoshop does Photoshop applies Brightness/Contrast in a CMYK document to each ink's stored value, 1 - ink, black included. Both the modern and the legacy curve do this; the cmyk8 brightness-contrast(-legacy) oracles match it within a level on every pixel of the files' own inks. Raising brightness takes ink away. We applied it to the screen colour instead. - cmyk_channel_adjustment gains Brightness/Contrast. apply_in builds the channel curve once (brightness_contrast_lut) and runs each separated ink through it (ink_through). - Destructive Image > Adjustments on a CMYK layer curves the stored inks directly, so it is exact; a selection mixes them. adjusted_channels now takes the per-pixel operation, and works out luma only for CMYK Threshold, which compares it. - The GPU leaves CMYK Brightness/Contrast to the CPU, like the other ink rules. cmyk8/16 brightness-contrast oracles, bad pixels: - modern: 72% -> 48-57%, max error 0.19 -> 0.09 - legacy: 71% -> 51-53% The rest is our separation of the RGB composite, not the rule. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * CMYK Threshold compares the inks' own luma, as Photoshop does Photoshop's CMYK Threshold splits on the Rec. 601 luma of the inks' plain complement, (1 - c)(1 - k) and so on, whatever the document's profile. On the files' own inks this puts every pixel of cmyk8 and cmyk16 threshold-128.psd on the right side of level 128. The profile's RGB luma missed 100. stored_channels works the luma out from the inks itself (ink_luma), so it no longer takes one; the engine's stored-channel path no longer converts each pixel to RGB at all. Through the separated RGB composite the cmyk threshold oracles drop from 1.6% to 0.2% bad pixels. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * CMYK legacy Brightness/Contrast pivots at 128 in ink Photoshop's legacy contrast pivots at level 128 of the ink, which is 127 of 255 of the stored value (1 - ink) that the curve runs on, not 128 as in RGB. On Photoshop's own 16-bit inks (cmyk16 brightness-contrast-legacy.psd) ours sat a constant 0.43 of a level above. That is exactly the one-level pivot shift times contrast +30's slope minus one; with the pivot moved, the inks match within 0.01. brightness_contrast_lut is now ink_brightness_contrast_lut, since its legacy curve is the CMYK one. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * CMYK: adjustment layers composite on the document's own inks The compositor works in display RGB. In a CMYK document, an adjustment layer that Photoshop evaluates on the inks could only act on our separation of the RGB composite, and that separation's black differs from the file's. So even exact ink rules missed: CMYK Invert was 10% off, Levels and Curves 50-65%. The ink-native compositor (compose::native, until now only for flattening plain raster stacks) now takes adjustment layers too: - Invert, Posterize, Threshold and Brightness/Contrast (modern and legacy), and Levels and Curves on CMYK channels, prepared once (InkStack, InkOp) and applied to the straight inks. - Opacity and an unfeathered layer mask mix the inks linearly, as in Photoshop; raster layers' masks scale their coverage the same way. - A CMYK stack of plain raster layers and such adjustments renders this way for display, export and reduced views (render_cmyk, tiles in parallel); flattening and merging keep the adjusted inks exactly. - Stacks of raster layers alone keep the RGB compositor, which the GPU matches. The GPU already leaves these adjustments to the CPU. Photoshop oracles: cmyk8 and cmyk16 invert, posterize-4, threshold-128, levels, curves, brightness-contrast and brightness-contrast-legacy all pass (14 files), 151 -> 165 of 258; floor 151 -> 165. psd-tools and io corpora unchanged. 24 MP CMYK8 with one adjustment renders in 286 ms on the inks, against 442 ms through the RGB compositor. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * CMYK ink compositing inlines open groups The ink compositor gave up on any group. Now a group at full opacity without a mask is inlined: - a pass-through group's children composite straight onto the backdrop, so an adjustment inside it reaches the layers below; - an isolated (Normal) group of raster layers alone composites as its children would, since Normal is associative. An isolated group with an adjustment, which only sees the group's content, keeps the RGB compositor. So do a translucent group and an artboard. Nesting is bounded. psd-tools' CMYK adjustment files keep their swatches in pass-through groups. With #4948's fair comparison, curves_cmyk drops from 37% to 0.3% bad pixels and levels_cmyk from 14% to 0.2%. The photoshop corpus is unchanged at 165. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * CMYK: Hue/Saturation and Color Balance keep the black ink In a CMYK document Photoshop applies Hue/Saturation (not Colorize) and Color Balance to C, M and Y as the complement of an RGB colour, and leaves the black ink alone. On the photoshop corpus's own inks, cmyk16 hue-saturation.psd follows this on every pixel within half a level (cmyk8 within two), and color-balance within our RGB Color Balance's own error. We applied both to the separated screen colour, which also rewrote K. - adjust::cmy_adjustment and apply_cmy run the RGB adjustment once per band on (1 - c, 1 - m, 1 - y). - The ink compositor (InkOp::Cmy), the RGB compositor's CMYK branch and destructive Image > Adjustments (pixels::adjusted_cmy) use them. The GPU leaves these to the CPU in CMYK documents, as it does the other ink rules. - Colorize separates its colour again, black included, so it keeps the screen-colour path. cmyk8/16 oracles, bad pixels: - hue-saturation: 100% -> 0.4-0.7% - color-balance: 74% -> 25% Neither passes yet. Half a level of cyan ink is three levels of red through the profile at saturated cyan, and our RGB models leave that much. The pass count stays at 165. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * 32-bit: legacy Brightness/Contrast, Channel Mixer, Photo Filter and B&W tint unclipped In 32-bit documents Photoshop keeps these adjustments' results above 1 and below 0. On the photoshop corpus's rgb32/gray32 files: - Legacy Brightness/Contrast pivots its contrast at 127 of 255 (8/16-bit: 128) and is exact on every pixel. - Channel Mixer cuts each source percentage to 1/1024 toward zero, counts 255/512 of the constant and is exact on pure red, green, blue, black and white. - Photo Filter works on the linear samples, negative results included. - The Black & White tint is the Color blend mode without the clip at 1, as the blend mode is there; white tints to (1.05, 1.00, 0.87). We clipped all four to 0..1. The GPU kernels follow suit under F_HDR (the legacy pivot and the mixer's steps come from the planner), and the HDR parity test covers them. Photoshop oracles: rgb32 and gray32 brightness-contrast-legacy, rgb32 channel-mixer and black-white-tint pass (145 -> 149 of 258); floor 145 -> 149. rgb32 photo-filter improves (0.19 -> 0.035 max); the rest is its colour (#3790). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * Modern brightness: knee at output 126, fit out to -95 and +150 psd-tools' brightnesscontrast_rgb.psd masks four Brightness/Contrast layers to their own columns. Read through the exact contrast curve, it gives Photoshop's brightness at -95, -31, +23 and +150, well past the +/-50 samples the first fit had. The +/-50 curve extrapolated badly there: 22 levels off at -95 and 25 at +150. Every setting puts the knee at about the same output level, not input. The roll-off's end slope falls as 1/(1 + 0.084 b). With the knee at 126/255 and that end slope, the cubic Hermite fits -95, -50, -31, +23, +25 and +50 within 1.4 levels. Past about +110 no such cubic stays below white, so there the roll-off is 1 - (1 - y0)(1 - u)^alpha, with the slope continuous at the knee. That gives +150 within 6 levels, where every curve family tried bottoms out. Lowered curves are still the inverse of raised ones. The photoshop corpus's six brightness-contrast oracles still pass. psd-tools brightnesscontrast_rgb goes from 0.13 to 0.020 max error and _grayscale from 0.098 to 0.016. The new measurements are pinned in modern_brightness_matches_photoshop. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * Levels: whole levels at every step and Photoshop's shadow toe In 8 bits Photoshop rounds each of the three Levels steps to a whole level (half up): the input-range stretch (already modelled), the midtone gamma and the output range. A narrow output range therefore merges neighbouring gamma levels: psd-tools levels_rgb maps R 43..48 to 58 through a 0.47 channel gamma and the master's 48..255, where the unrounded curve gave 56..59 (3 levels off in blue). The gamma above 1 starts along a toe a*u - b*u^q of slope a = 2^gamma that joins the power curve with the same value and slope (q = 2.2, fitted). With the rounding, that is exact on 1116 of the 1118 levels of gamma 1.16, 1.22, 1.3, 1.78 and 2.0 oracles; the soft-min it replaces missed 52. Gamma below 1 stays the plain power curve (0.67 and 0.7: every level exact). Oracles: psd-tools levels_rgb 0.0118 -> 0.0039 (PASS); photoshop rgb8/stack-levels-curves-hue-posterize 0.2000 -> 0.0000 (PASS); rgb8 and gray8 levels.psd 0.0039 -> 0.0000; rgb16/gray16 0.0039 -> 0.0020. Floors: photoshop 145 -> 146, psd-tools 236 -> 238 (main is at 237). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * Masks: feathers blur with exactly the feather's variance A mask feather is a Gaussian with sigma = feather, which we approximate with three box passes per axis. Whole-pixel boxes rounded the variance: a 6 px feather blurred like 6.48 px and a 3 px one like 3.46 px, so feathered edges were too soft by up to 4 levels against Photoshop (psd-tools mask-parameters-no-real-channel.psd: a 6 px vector and 3 px pixel feather). Each pass is now an "extended box" (Gwosdek et al. 2011): weight 1 on the whole radius and a fractional weight on the two samples beyond it, so three passes have variance sigma^2 exactly. It stays O(n), reusing the window's leaving sample for the low end weight (50 MP at a 1000 px feather: 180 ms parallel, was 172). psd-tools: mask-parameters-no-real-channel 0.0168 -> 0.0060 (PASS), layer_mask_data.psd 26.9 % -> 3.9 % of pixels off (psb 25.9 % -> 1.8 %). Corpus test 239 -> 240; floor 236 -> 240. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * Lab: adjustment layers composite on the stored L, a and b The compositor reads a Lab document's layers through display RGB, which clips colours outside its gamut, so the adjustments Photoshop evaluates on L, a and b (Invert, Posterize, Threshold, Brightness/Contrast, Levels and Curves with Lab records) only saw the clipped colours: the photoshop corpus's Lab oracles were up to 11 levels off on saturated colours. compose::native_lab works a Lab stack of plain layers out on the stored values instead, like the CMYK ink path: Normal mixes L, a and b linearly, an opaque layer keeps them exactly, a layer mask scales the mix, and adjustment layers run adjust::lab_stored_op on each pixel. Stacks with such adjustments render for display this way; flattening a plain Lab stack keeps its stored values (exports no longer clip). Anything else (other blend modes, effects, other adjustments) keeps the RGB compositor. Photoshop oracles 145 -> 152: lab16 invert, posterize-4, levels, curves and brightness-contrast-legacy; lab8 invert and posterize-4. lab8 levels and legacy B/C come within a level (their 8-bit rules are #5143 and #5132). psd-tools and io unchanged; every round trip unchanged. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * Threshold: split on Photoshop's luminosity of whole samples Photoshop's Threshold splits on the luminosity 0.30 R + 0.59 G + 0.11 B (the blend modes' lum, as Gradient Map uses), not the Rec. 601 grey, taken over the document's whole sample values: - 8 bits: 30 R + 59 G + 11 B > 100 level - 50, i.e. the luminosity rounded to a level with halves down reaches the level; - 16 bits: 30 R + 59 G + 11 B >= 100 x the level in 16 bits (round(level x 32768 / 255): mid grey 16448 is level 128); - 32 bits: the luminosity reaches the level. Exact on every pixel of psd-tools threshold_rgb (36432 px; Rec. 601 split 28 the other way), threshold_16bits_rgb (100) and threshold_16bits_ grayscale, and the photoshop corpus's rgb16 threshold-128. The sums are exact in f32, on the CPU and in the GPU kernel, so ties (grey exactly on the level) split the same way on both. psd-tools: threshold_rgb and threshold_16bits_rgb pass; corpus test 239 -> 241, floor 236 -> 241. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * Posterize: 16-bit documents bin the 16-bit sample, as Photoshop does At 16 bits Photoshop doesn't round to 8-bit levels before binning. It bins the 16-bit sample, floor(v16 * n / 32768), and lands on 8-bit levels through a 16-bit step: floor(b * 32768 / (n - 1)), converted with floor((o * 255 + 16384) / 32768). So the middle of 3 levels is 128 where 8 bits give 127, while 42.5 and 25.5 stay 42 and 25. Exact on every sample of psd-tools posterize_16bits_rgb (levels 3, 7, 13, 21) and posterize_16bits_grayscale (2, 6, 9, 11); the 8-bit rule missed up to half the range at bin edges. The same rule applies to CMYK and Lab channels at 16 bits: on the stored inks (#4945's native path) psd-tools posterize_16bits_cmyk goes from 4.26 % to 0.01 % of pixels off. 8-bit Posterize is unchanged. The GPU kernel runs the same rule; 16-bit layers reach it as half floats, so a sample within their precision of a bin edge can land in the neighbouring bin there (the CPU, which exports, is exact). psd-tools 239 -> 241; floor 236 -> 241. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * CMYK: Posterize works on the stored values (1 - ink) Photoshop posterizes a CMYK channel's stored value, 1 - ink, not the ink: with levels whose steps are uneven (3, 7, 13, 21) the two differ, e.g. 3 levels take an ink of 85 to 128, where posterizing the ink drops it to none. psd-tools posterize_cmyk.psd goes from 13.8 % of pixels off to exact; psd-tools 241 -> 242, floor 242. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * Groups: a pass-through clipping base with an adjustment renders isolated A pass-through group composites its children straight into the backdrop, so an adjustment layer inside reaches the layers beneath. When the group is the base of a clipping group and holds an adjustment layer, Photoshop renders it isolated instead: in psd-tools passthrough_clipping_mask_adjustment an Exposure in such a group leaves the layers beneath alone (we darkened them: half the image 170 levels off). The same group with a Linear Dodge child and no adjustment keeps reaching the backdrop (passthrough_clipping_mask_blendmode), and so do clipping-mask3/4/5, so the rule is the adjustment, not the clipping alone (isolating every pass-through clipping base broke those two). CPU compositor and GPU plan alike. psd-tools 239 -> 240; floor 240. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * Raise corpus floors to the results of the landed adjustment fixes Photoshop-authored 165 -> 185 of 258, io 146 -> 148 of 170, psd-tools 242 -> 249 of 309, measured with the CMYK, Lab, 32-bit, Levels, Threshold, Posterize, feather and pass-through PRs merged together. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> --------- Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com> Co-authored-by: Brandon Thomas <echelon@gmail.com>