Imatest Documentation

Recommendations

Info

Imatest Documentation Noise in photographic images Introduction Noise is a random variation of image density, visible as grain in film and pixel level variations in digital images. It is a key image quality factor; nearly as important as sharpness. Since it arises from basic physics— the photon nature of light and the thermal energy of heat— it will always be there. The good news is noise can be extremely low— often impreceptably low— in digital cameras, particularly DSLRs with large pixels (5 microns square or larger). But noise can get ugly in compact digital cameras with tiny pixels, especially at high ISO speeds. In most cases noise is perceived as a degradation in quality. But some Black & White photographers like its graphic effect: Many favor 35mm 35mm Tri-X film. The pointillist painters, most notably George Seurat, created "noise" (specks of color) by hand; a task that can be accomplished in seconds today with Photoshop plugins. But by and large, the majority of photographers, especially color and large-format photographers, dislike noise with good reason. Noise is measured by several Imatest modules. Stepchart produces the most detailed results, but noise is also measured in Colorcheck, SFR, and Light Falloff. Appearance The appearance of noise is illustrated in the stepchart images on the right. Noise is usually measured as an RMS (root mean square) voltage. The mathematics of noise is presented in a green box at the bottom of this page. The stepcharts in columns (A)-(C) are simulated. They are assumed to have a minimum density of 0.05 and density steps of 0.1, identical to the Kodak Q-13 and Q-14. They have been encoded with gamma = 1/2.2 for optimum viewing at gamma = 2.2 (the Windows/Internet standard). Strong noise— more than you'd find in most digital cameras— has been added to columns (A) and (B). Column (C) is noiseless. The fourth column (D) contains an actual Q-13 stepchart image taken with the Canon EOS-10D at ISO 1600: a very ISO high speed. Noise is visible, but admirably low for such a high ISO speed (thanks, no doubt, to software noise reduction). The noise in (A) is constant inside the sensor, i.e., before gamma encoding. When it is encoded with gamma = 1/2.2, contrast, and hence noise, is boosted in dark areas and reduced in light areas. The Kodak publication, CCD Image Sensor Noise Sources, indicates that this is not a realistic case. Sensor noise tends to increase with brightness. The noise in (B) is uniform in the image file, i.e., its value measured in pixels is constant. This noise must therefore increase with brightness inside the sensor (prior to gamma encoding), and hence is closer to real sensor behaviour than (A). Noise appears relatively constant except for the darkest zones, where it's not clearly visible. Noise is often lower in the lightest zones, where a tonal response "S" curve superimposed on the gamma curve (or saturation) reduces contrast, hence noise. For this reason the middle zones— where noise is most visible— are used to calculate the average noise: a single number used to characterize overall noise performance. We omit zones where the density of the original chart (hence display density in an unmanipulated image) is greater than 1.5 or less than 0.1. Noise measurements Noise measurements should ideally (A) Const. sensor noise (B) Const. pixel noise (C) No noise (D) Canon EOS-10D ISO 1600 18 of 451
Imatest Documentation correlate with perceived appearance, (in many cases) be referenced to the original scene so the measurement is not affected by the tonal response (contrast) of the camera or RAW converter, be detailed enough to allow accurate assessment of sensor and camera performance, and be simple enough to interpret without difficulty. Since noise is only meaningful in relationship to a signal, a Signal-to Noise Ratio (SNR or S/N) is often calculated. SNR can be defined in many ways, depending on how Signal S is defined. For example, S can be an individual patch pixel level or the pixel difference corresponding to a specified scene density range (1.45 or 1.5 are often used for this purpose). It is important to know precisely how SNR is defined whenever it is discussed. SNR can be expresed as a simple ratio (S/N) or in decibels (dB), where SNR (dB) = 20 log10(S/N). Doubling S/N corresponds to increasing SNR (dB) by 6.02 dB. Since these requirements can be somewhat contradictory, Imatest modules have several noise and SNR measurements, some simple and some detailed. Available displays in Stepchart and Colorcheck include: Noise a function of pixel level or exposure, expressed in Pixels, normalized to the pixel difference corresponding to a scene density range of 1.5 for Stepchart (comparable to the density range of 1.45 for the GretagMacbeth ColorChecker) or the White - Black zones in the ColorChecker (row 3, patches 1 - 6; density range = 1.45). Without this normalization, noise is a function of RAW converter response curve; it increases with converter contrast. Pixels, normalized to the maximum pixel value: 255 for 8/24-bit files. Pixels (maximum of 255 for 8/24-bit files) f-stops (or EV or zones; a factor of two in exposure), i.e., referenced to the original scene. Noise measured in f-stops corresponds closely to human vision. See f-stop noise, below. Noise as a simple (average) number A good single number for describing noise is the average noise of the Y (Luminance) channel, measured in pixels (normalized scene density difference of 1.5), shown in the lower plot in the figures, below. The lightest and darkest zones, representing chart densities greater than 1.5 or less than 0.1 are excluded from the average. S/N or SNR (dB) as a function of pixel level or exposure, where S is the pixel level of the individual test chart patch. S/N or SNR (dB) as a simple (average) number. A good single number for defining SNR is the White - Black SNR, SNR_BW, where S is the difference in pixel levels between the White and Black patches in the GretagMacbeth ColorChecker in Colorcheck (density range of 1.45), or the pixel difference corresponding to a chart (scene) density difference of 1.5 in Stepchart. Noise N is taken from a middle level patch with density around 0.7. SNRBW = 20 log10(( SWHITE – SBLACK ) / Nmid ) a noise spectrum plot, described below. In addition, Light Falloff displays a spatial map of noise. Characteristic Stepchart results are shown below. Column (B): Uniform pixel noise 19 of 451
Page 1 and 2: Imatest Documentation © 2009 Imate
Page 3 and 4: Imatest Documentation Using SFRplus
Page 5 and 6: Imatest Documentation Image Quality
Page 7 and 8: Imatest Documentation tilted (about
Page 9 and 10: Imatest Documentation MTF50 in Line
Page 11 and 12: Imatest Documentation SQF Subjectiv
Page 13 and 14: Imatest Documentation RAW converter
Page 15 and 16: Imatest Documentation cm (4 inch) h
Page 17: Imatest Documentation CSF( f ) = 2.
Page 21 and 22: Imatest Documentation Unlike the ab
Page 23 and 24: Imatest Documentation Since luminan
Page 25 and 26: Imatest Documentation committee" (I
Page 27 and 28: Imatest Documentation The formula f
Page 29 and 30: Imatest Documentation The image to
Page 31 and 32: Imatest Documentation Sharpness com
Page 33 and 34: Imatest Documentation (DPR) Canon E
Page 35 and 36: Imatest Documentation but their noi
Page 37 and 38: Imatest Documentation The average t
Page 39 and 40: Imatest Documentation Chromatic abe
Page 41 and 42: Imatest Documentation Veiling glare
Page 43 and 44: Imatest Documentation A Kodak Q-13
Page 45 and 46: Imatest Documentation with UV filte
Page 47 and 48: Imatest Documentation Czajkowski' r
Page 49 and 50: Imatest Documentation P_Rm = O_Rm*A
Page 51 and 52: Imatest Documentation Split view, s
Page 53 and 54: Imatest Documentation ISO Sensitivi
Page 55 and 56: Imatest Documentation Multicharts T
Page 57 and 58: Imatest Documentation Shoulders are
Page 59 and 60: Imatest Documentation Related docum
Page 61 and 62: Imatest Documentation between image
Page 63 and 64: Imatest Documentation We display va
Page 65 and 66: Imatest Documentation Blur units, M
Page 67 and 68: Imatest Documentation σ 2 = Σ (ti
Page 69 and 70:
Imatest Documentation Drill holes l
Page 71 and 72:
Imatest Documentation rummaging thr
Page 73 and 74:
Imatest Documentation Target size C
Page 75 and 76:
Imatest Documentation Level the tar
Page 77 and 78:
Imatest Documentation Kodak Q-14 St
Page 79 and 80:
Imatest Documentation Imatest Instr
Page 81 and 82:
Imatest Documentation in the Imates
Page 83 and 84:
Imatest Documentation samples (fold
Page 85 and 86:
Imatest Documentation Using Imatest
Page 87 and 88:
Imatest Documentation About RAW fil
Page 89 and 90:
Imatest Documentation Options I for
Page 91 and 92:
Imatest Documentation Special user
Page 93 and 94:
Imatest Documentation CSV files- Ex
Page 95 and 96:
Imatest Documentation RAW files RAW
Page 97 and 98:
Imatest Documentation dcraw The ori
Page 99 and 100:
Imatest Documentation The Rawview w
Page 101 and 102:
Imatest Documentation identical (th
Page 103 and 104:
Imatest Documentation The Imatest T
Page 105 and 106:
Imatest Documentation Tripod and ac
Page 107 and 108:
Imatest Documentation Targets Chart
Page 109 and 110:
Imatest Documentation Left of cente
Page 111 and 112:
Imatest Documentation Rope trick (f
Page 113 and 114:
Imatest Documentation Distortion ta
Page 115 and 116:
Imatest Documentation If you fail t
Page 117 and 118:
Imatest Documentation Diagnostics r
Page 119 and 120:
Imatest Documentation A horizontal
Page 121 and 122:
Imatest Documentation the edges pri
Page 123 and 124:
Imatest Documentation The camera mu
Page 125 and 126:
Imatest Documentation Epson 2200 Pr
Page 127 and 128:
Imatest Documentation Using SFR Par
Page 129 and 130:
Imatest Documentation ROI fine adju
Page 131 and 132:
Imatest Documentation Pixel size ha
Page 133 and 134:
Imatest Documentation contrast in h
Page 135 and 136:
Imatest Documentation Two precautio
Page 137 and 138:
Imatest Documentation The PNG files
Page 139 and 140:
Imatest Documentation nroi = 9 nwid
Page 141 and 142:
Imatest Documentation An optional .
Page 143 and 144:
Imatest Documentation SFR results:
Page 145 and 146:
Imatest Documentation Right column
Page 147 and 148:
Imatest Documentation Right: Input
Page 149 and 150:
Imatest Documentation Below the plo
Page 151 and 152:
Imatest Documentation Multi-ROI 2D
Page 153 and 154:
Imatest Documentation The Legend at
Page 155 and 156:
Imatest Documentation MTF50 (Cy/Pxl
Page 157 and 158:
Imatest Documentation Summary plot
Page 159 and 160:
Imatest Documentation 3D Plot for M
Page 161 and 162:
Imatest Documentation The standard
Page 163 and 164:
Imatest Documentation degrees are i
Page 165 and 166:
Imatest Documentation Using SFRplus
Page 167 and 168:
Imatest Documentation SFRplus setup
Page 169 and 170:
Imatest Documentation SFRplus setti
Page 171 and 172:
Imatest Documentation Gamma Gamma i
Page 173 and 174:
Imatest Documentation Using SFRplus
Page 175 and 176:
Imatest Documentation Weighted MTF5
Page 177 and 178:
Imatest Documentation This display
Page 179 and 180:
Imatest Documentation space of the
Page 181 and 182:
Imatest Documentation window, shown
Page 183 and 184:
Imatest Documentation It's easy to
Page 185 and 186:
Imatest Documentation Using Reschar
Page 187 and 188:
Imatest Documentation Select an ima
Page 189 and 190:
Imatest Documentation MTF contours
Page 191 and 192:
Imatest Documentation SFRplus SFR H
Page 193 and 194:
Imatest Documentation Log F-Contras
Page 195 and 196:
Imatest Documentation Log Frequency
Page 197 and 198:
Imatest Documentation Color moiré
Page 199 and 200:
Imatest Documentation The display o
Page 201 and 202:
Imatest Documentation phase) is twi
Page 203 and 204:
Imatest Documentation Downloadable
Page 205 and 206:
Imatest Documentation If Express mo
Page 207 and 208:
Imatest Documentation The display o
Page 209 and 210:
Imatest Documentation The differenc
Page 211 and 212:
Imatest Documentation Star Chart An
Page 213 and 214:
Imatest Documentation ROI fine adju
Page 215 and 216:
Imatest Documentation MTF (linear f
Page 217 and 218:
Imatest Documentation The plot on t
Page 219 and 220:
Imatest Documentation MTF Compare C
Page 221 and 222:
Imatest Documentation MTF Compare r
Page 223 and 224:
Imatest Documentation Comparison of
Page 225 and 226:
Imatest Documentation Batchview Pos
Page 227 and 228:
Imatest Documentation Rescharts SFR
Page 229 and 230:
Imatest Documentation Running Batch
Page 231 and 232:
Imatest Documentation Center mean O
Page 233 and 234:
Imatest Documentation standard mono
Page 235 and 236:
Imatest Documentation Lighting Inte
Page 237 and 238:
Imatest Documentation Run Imatest S
Page 239 and 240:
Imatest Documentation SFRplus setup
Page 241 and 242:
Imatest Documentation SFRplus setti
Page 243 and 244:
Imatest Documentation Additional pa
Page 245 and 246:
Imatest Documentation Output files
Page 247 and 248:
Imatest Documentation Lens-style MT
Page 249 and 250:
Imatest Documentation File formats
Page 251 and 252:
Imatest Documentation Purchase or d
Page 253 and 254:
Imatest Documentation Sharpness tar
Page 255 and 256:
Imatest Documentation Proper exposu
Page 257 and 258:
Imatest Documentation If you answer
Page 259 and 260:
Imatest Documentation SFR input dia
Page 261 and 262:
Imatest Documentation Figures (.PNG
Page 263 and 264:
Imatest Documentation contrast imag
Page 265 and 266:
Imatest Documentation Chromatic Abe
Page 267 and 268:
Imatest Documentation QA-61 ISO-160
Page 269 and 270:
Imatest Documentation Stepchart inp
Page 271 and 272:
Imatest Documentation First Figure:
Page 273 and 274:
Imatest Documentation Third Figure:
Page 275 and 276:
Imatest Documentation A camera's (o
Page 277 and 278:
Imatest Documentation The total dyn
Page 279 and 280:
Imatest Documentation Gamc is typic
Page 281 and 282:
Imatest Documentation ISO-15739 Noi
Page 283 and 284:
Imatest Documentation You can enter
Page 285 and 286:
Imatest Documentation Results If RA
Page 287 and 288:
Imatest Documentation Dynamic range
Page 289 and 290:
Imatest Documentation Using Colorch
Page 291 and 292:
Imatest Documentation horizontal fi
Page 293 and 294:
Imatest Documentation Colorcheck in
Page 295 and 296:
Imatest Documentation The first fig
Page 297 and 298:
Imatest Documentation The backgroun
Page 299 and 300:
Imatest Documentation saturated gre
Page 301 and 302:
Imatest Documentation (blank line)
Page 303 and 304:
Imatest Documentation CMC An early
Page 305 and 306:
Imatest Documentation The the equat
Page 307 and 308:
Imatest Documentation Multicharts o
Page 309 and 310:
Imatest Documentation If you select
Page 311 and 312:
Imatest Documentation The Zoom chec
Page 313 and 314:
Imatest Documentation + b* Pseudoco
Page 315 and 316:
Imatest Documentation Shows the gra
Page 317 and 318:
Imatest Documentation Multicharts S
Page 319 and 320:
Imatest Documentation Read from a 5
Page 321 and 322:
Imatest Documentation Use these ord
Page 323 and 324:
Imatest Documentation Color correct
Page 325 and 326:
Imatest Documentation Options: Colo
Page 327 and 328:
Imatest Documentation Exif and Colo
Page 329 and 330:
Imatest Documentation The Labsphere
Page 331 and 332:
Imatest Documentation Scaling butto
Page 333 and 334:
Imatest Documentation F-stop contou
Page 335 and 336:
Imatest Documentation Uniformity (L
Page 337 and 338:
Imatest Documentation density— vi
Page 339 and 340:
Imatest Documentation the Corner an
Page 341 and 342:
Imatest Documentation The local noi
Page 343 and 344:
Imatest Documentation Local nonunif
Page 345 and 346:
Imatest Documentation Image with sp
Page 347 and 348:
Imatest Documentation Using Distort
Page 349 and 350:
Imatest Documentation Set exposure
Page 351 and 352:
Imatest Documentation Plot distorti
Page 353 and 354:
Imatest Documentation Imatest will
Page 355 and 356:
Imatest Documentation MTF (sharpnes
Page 357 and 358:
Imatest Documentation Intersection
Page 359 and 360:
Imatest Documentation function of r
Page 361 and 362:
Imatest Documentation Imatest Instr
Page 363 and 364:
Imatest Documentation Horizontal di
Page 365 and 366:
Imatest Documentation Zone plates (
Page 367 and 368:
Imatest Documentation Along with ch
Page 369 and 370:
Imatest Documentation Preview image
Page 371 and 372:
Imatest Documentation Light Falloff
Page 373 and 374:
Imatest Documentation Monitor Calib
Page 375 and 376:
Imatest Documentation Black level (
Page 377 and 378:
Imatest Documentation Reset pattern
Page 379 and 380:
Imatest Documentation SVG Test Char
Page 381 and 382:
Imatest Documentation SVG SFR chart
Page 383 and 384:
Imatest Documentation To run Test C
Page 385 and 386:
Imatest Documentation Invert light/
Page 387 and 388:
Imatest Documentation Contrast (alt
Page 389 and 390:
Imatest Documentation window. Print
Page 391 and 392:
Imatest Documentation files. Quick
Page 393 and 394:
Imatest Documentation File selectio
Page 395 and 396:
Imatest Documentation Imatest IT/EX
Page 397 and 398:
Imatest Documentation cyclesper_val
Page 399 and 400:
Imatest Documentation optional. The
Page 401 and 402:
Imatest Documentation Change to the
Page 403 and 404:
Imatest Documentation Detailed inst
Page 405 and 406:
Imatest Documentation Scanner profi
Page 407 and 408:
Imatest Documentation Although this
Page 409 and 410:
Imatest Documentation Gamut is exce
Page 411 and 412:
Imatest Documentation S=1 HSL Hue p
Page 413 and 414:
Imatest Documentation An additional
Page 415 and 416:
Imatest Documentation Instructions
Page 417 and 418:
Imatest Documentation 7. 8. Mask im
Page 419 and 420:
Imatest Documentation 9. Corr Image
Page 421 and 422:
Imatest Documentation Appendix Cros
Page 423 and 424:
Imatest Documentation Sorted by tes
Page 425 and 426:
Imatest Documentation Distortion Un
Page 427 and 428:
Imatest Documentation Create Scalab
Page 429 and 430:
Imatest Documentation f-stop . Gamm
Page 431 and 432:
Imatest Documentation Glosario en E
Page 433 and 434:
Imatest Documentation Troubleshooti
Page 435 and 436:
Imatest Documentation You can selec
Page 437 and 438:
Imatest Documentation Imatest Chang
Page 439 and 440:
Imatest Documentation below, next t
Page 441 and 442:
Imatest Documentation Jan. 6, 2007
Page 443 and 444:
Imatest Documentation Nov. 6, 2005
Page 445 and 446:
Imatest Documentation Sept. 11, 200
Page 447 and 448:
Imatest Documentation XML Changes N
Page 449 and 450:
Imatest Documentation License The I
Page 451:
Imatest Documentation 11. GENERAL T
show all

Imatest Documentation

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?