CA2192104A1 - Apparatus for use in color correction in an electronic imaging system - Google Patents

Abstract

A system for predicting and correcting color casts in digital images is described. A means of computing (predicting) color cast candidates from scanned image data, and a means of selecting from this set of candidates casts the last objectionable cast based on user interaction is presented.

Description

WO 96/3~29~ o Is l7 21g2104 APPARATUS FOR USE IN COLOR CORRECTION IN AN
ELECTRONIC IMAGING SYSTEM
FIELD OF THE INVENTION
This invention, in general, relates to the field of electronic imaging devices and, more ~ ul~ly, to apparatus and methods for use in such devices for editing tone range and correcting for color errors.
BACKGROUND OF THE INVENTION
It is well understood that the perceived colors from objects depend on thei}
spectral reflection 1 ~ t ~ - ` and the spectral content of the sources which illu~ninate them. Objects that are neutral in color, that is, those which reflect equal amounts of an adopted set of primary colors, will appear neutral gray when min~t~d by a source that is spectrally flat. For example, a neutral gray object min~t.~d by a spectrally flat source such as noontime sunlight, which has a uniform spectral power ~ tnhlltifm will appear more or less neutral to an observer.
If a light source differs from neutral, it is said to have a "color cast" since its spectral content is no longer flat with wavelength, but rather, contains more of one "color"
than another. It, therefore, has a dominant "cast" which makes it less 'pure" than a neutral "white" light. For example, tungsten sources have relatively more red light than blue so will have a "reddish cast". Fluorescent lights, on the other hand, tend to the "greenish" part of the spectrum, and hence have "green casts".
Obviously, the color appearance of even neutral objects, whether in reflectance or ~ , e, is influenced dramatically by the cast of the source min~tinE them. And, where objects inherently are of one cast themselves, that cast can be distorted in color appearance to be something other than it would appear under neutral lighting.
While color cast issues are relatively easy to .~ l_lr to human observers since they can see what is taking place when differently reflecting objects are illurninated by sources of different casts, what takes place when a nonhuman detector does not have the same spectral response ~1, . ,.. ~ . ;~1;. . of the human visual -I -wo 96/3529~ o ls ~7 21g2104 ' ayStem is somewhat more subtle, but in principle similar if one cam mlagine }eplacing the spectral response of the receiver for that of a human observer. Like the human visual system other light detectors have preferential spectral a~l~;Livi~
which also vary with W~ L lly,LII. Video cameras and film scanners, for example,differ ai~l;fi~,~Lly from the hu~nan visual system in their response to color, yet all can "see" color but in different ways. Co~ ..ly, the response of the detector ofcolor can introduce or modify the "color cast" of an image, and that color cast component will be seen by an observer as am additiorl~l color distortion. Thus, color cast problems are pervasive in electronic imaging systems" " r ~ themselves in a variety of ways which make images have an 'bnreal" or 'bnnatural" color appearance to a human observer.
One example of color cast occurs in the electronic scarming and display of images. When scanrling color ~ .l, materials (reflection prints or Llf~ h ~) usmg am electronic scalmer, and ~ f ~ ly, displaying the scalmed image ~fia a monitor after applying a color transform of some sort, the displayed image often appears with an ~ 1 lF color cast which is l uvl~,~ullle because it is unnatural in ~rpf.~r~nrr Such color casts can be attributed to a variety of sources mcluding, but not limited to, scene illlmninrtinn conditions during a~ exposure,variationinthel ,~ ofthel.l...lu~ ~ . materials themselves, ambient ~ conditions, or variations in subsequent chemical processing.
The color cast problem has been dealt with in a variety of ways depending on the context in which it appears. In labs for the processing and prmting of CUIl~,llLiull~ r films, controls for color cast removal are provided to the operator who assesses the degree of cast and manually adjusts for its removal. In many such systems today, automatic color cast removal is;, . ,l,l. . ". ~t 1 by way of a low-resolution video camera which observes the processed negative, performs a calculation on the resulting data, and provides some form of correction to the negative-printing system. The rnmrllf~tinnc typically are based on computing the

-2 -~096/3~291 2I9Z104 t~ osl7 average color level m a negative which, on ave}age, will produce a neutral gray in the print.
Consumer camcorders use a slightly different approach which deals primarily with variations in the illuminamt color t~ laLul~. Most operate by attempting todetermine a white object in the scerle, and then infer a scene color cast from the white pomt cast. Capture circuitry is then 1~ ' ' ' "on-the-fly" as recording continues. These mPthr~ lovj~-~ are sometimes referred to as automatic gain control (AGC) and automatic white point control for correcting for differences in the illumin~mt's color ~ .,LaL~i, a measure of the color content of the illuminant.
Color copiers may employ steps similar to those above or various ~mhin~tirmc of them.
Image processmg software often provides for user adjustment of color cast by way of manual control over color content through the use of color sliders for R, G, B
content. However, in the _ands of am unskilled and,., I~ ~ . cd operator, such controls can be ~ lr and as l..vl.~ as they are beneficial.
While a number of approaches to the color cast problem have appeared m a variety of settings, it is a primary object of this invention to provide a systematic, highly automated m~th~ f logy for the removal of color cast for use in electronic imaging systems.
It is another object of the present invention to provide for the systematic l,,."~I'",.,.rl,nn display,andremovalofcolorcastsfromscannedhardcOPYimages displayed on color monitors.
It is yet another object of the present invention to provide for the automated editing of the tonal r~mge in a scarlned color hard copy of an image to assure that neutrals m the image appear visibly gray.
Other objects of the invention will appear obvious and will appear hereinaftff when reading the following detailed ~ rirtinn

-3 -Wo 96135291 2 1 9 2 1 ~ 4 ~ c 1347 ~, ;.
SUMMARY OF THE INVENTION
The invention is related to electrorlic color processing of images im the form of electronic signals and, in particular, to systems which are not wholly automatic but involve some operator sdection. It is applicable to electronic scanners used to scan ~ or other materials, ~ , electronic still cameras, video cameras, video or still picture image-editing software, or in the related alts. It may be used with systems usmg tbree or more color signals (e.g. RGB or CMYK).
Although the preferred r~ o~ 1 involves the use of digital signals, amalog signal processing to perform tEIese operations could aiso ~e . ~ Il It- 1 Regardless of the signal source, all aspects of the invention involve the use of a color display which is viewed by an operator.
The inventive system operates to remove color casts or color balance errors from images. The system consists of three main parts: a set of cast-prediction operators which operate on the source image data and coarse device profile data, a preview mechanism whereby an image can be displayed to the operator on a calibrated color display, and a mechanism for selecting between candidate casts computed by the cast-prediction operators - which are applied to the images and displayed to the user for evaludtion. The use of ~ images for image preview and cast-removal 1~", 1 ,1" . 1 1 ,"1 1 is 1~ . ~111111. . .~1. .1, but not required.
In one aspect of the invention, the operator obtains a source image and presents it to the system, along with the coarse device profile for the image acquisition system and a device profile for the display monitor. Using the frrst two datd sets, the system computes equivalent log-scene exposures (e.g. Red exposure, Green icxposure, Blue Exposure) for each pixel in the image. The cast predictionoperators compute a color cast from the log-scene exposure images using knowledge derived from the image datd and the known exposure balance (color balance or cast) of a neutral object in the scene -- which was provided as pa~t of the coarse profile datd dCC~ g the image. The cast predictions from each of the operators, now represented by a log exposure triplet ( e.g., R, G, B exposure) are stored in a memory.

wo 96/3529~ 947 2Ig21 04 In another aspect of the invention, the operator selects a cast prediction for preview.
In yet amother aspect of the invention, the image data is processed through the color processing system the operator normally uses to transform the input image data for display on the monitor, with mn-lifi~tinnc such that the selected color cast correction is applied. For example, if the image source is an input scanner having the property tbat scan data is ~UIU,UUl ~iUII~II to log-scene exposure for each of tbe color channels, cast correction may be introduced by adding an offset to each channel before sending the data to the color processor to compute an image for rendering on tbe display.
In the usual operating mode, an operator repeats the color tr~msform and preview operation for each of the cast predictions, amd tben selects the cast prediction having the preferred appear.mce. Additional cast correction could be performed in ~ ptinn~l cases using CU,~ tiullal means, begimling with the closest prediction from the above system.
DESCRIPTION OF THE DR~WINGS
The novel features that are considered .1,~ of the invention are set forthwithl~Li~uLu;L~/intheappendedclaims. Theinvention,itself,however,both as to its ~ ~ æ~ ;. ", amd method of operation, together with other objects amd advantages thereof, will best be umderstood from the following detailed description of the ~mhntlim~-ntc when read in connection with the a, ~u" ~ .yillg drawings wherein the same numerals have been used throughout the Yarious figures to denote the same features and wherem:
Fig. 1 is a .1; .~ ~ ; perspective view of an electronic imaging system in which the present invention is embodied;
Fig. 2 shows a fiow diagram for an ~ o.~;" . .~ of the invention in the form of a Ll~ llcy scanner amd associated ~ which implement the cast removal m~-thn~ ngy of the invention and ~ how preview and cast-removal modules of the invention interact with other system ~

wo 96/35291 2 1 9 2 1 0 ~ ~ ~.,1 c ,~ ~7 Fig.3isaflowdiagramfo}thè~" aL~ u~l moduleofFig.2,showing~e interaction ofthe cast c....~ .." preview, and cast selection, .... ~
Fig. 4 is a flow diagram of the color cast prediction module of the mvention;
and Fig. 5 shows a graphical user mterface by which the image preview and cast selection mf-fh~ni~m can be operated as part of an image-editing wulkakll;ul..
DETAILED DESCRIPTION
The invention in a preferred e",l-o.l;",. .,~ is described in connection with a color negative and ll~.,~cl~.,r scarmer As will be seen hereinafter, the scannerconsists of a transport light source, color CCD Imear array detector, a transport mf-e~ .m a preview memory, and a color tr,msform mrrh~ m Output from the scanner is digital data intended for display on a color monitor with output similar to the Apple 13 inch color monitor, IllalllJI`f~ by Apple Computer of Cupertino, California.
This system is designed to provide high quality digital color images from a wide variety of l IIuL,-~f~ flc negative and Llflla~f ~ Cll~,,r materials. Further, it is designed to be used by relatively unskilled operators who may or may not have significant knowledge of color reproduction systems, and need rapid scanning of their images. l'he major application for the scanner is in the desktop publishing application where the scarmer is attached to a personal computer used for image editing and display. As such, the scanner is controlled by and provides output data to host application software executing on a PC ~e.g. Adobe Photoshop by Adobe Systems, T~f"'1""- ' '~)-Reference is now made to Fig. 1 which shows an image-editing wul~al~Liull 20 embodying a preferred form of the invention. C omponents of the workstation 20 comprise a computer 22 used to perform operations on image data amd present a user with a graphical interface in the fûrm of dialogs on a co~or monitor 24, which is preferably calibrated. Color monitor 24 is also used for image preview amd display operations. A pointing device 28 and keyboard 26 fæilitate operator interætion Wo 96/35291 PCTIUS96/049~7 21921~
with other UUIIIUUII~,Il.~ of wul~Liiull 20. A disk drive 36 can be used for input or output of image files to or from a storage disk 34 or the like. Input signals can also originate from a digital still or motion video camera 30, but preferably originate from a Il~Aual~ "y scanner 32.
In general, the work station 20 allows an operator to place the scan media in the scanner, specify the material to be scanrled (e.g., color negative)along with the scan resolution and output size. A low resolution preview scan is performed and displayed to the user after havmg been color processed for viewing on the calibrated monitor. The user can then perform ~ on the scan parameters ( e.g., sharpening level, color cast removal, brighhness, cropping,...) while viewing aninteractive image preview showing the results of the ~ , tben initiate a final scan. A high resolution scan is then performed arld the data from the CCD array is ,ly processed tbrough the color processor and sent to the host ~MIir~hnn Figure 2 is a block diagram showing major ~ . ." ~ 0f the invention as it resides in ~ r~ 20 and is generally desigrlated as a system 50. As seen, system 50 comprises rh~togr~rhi~ negative image sampling module 52. Module 52 includes a light source 54 and a sensor 58 in the form of a CCD array. The makria being scarmed, m tbis case a color negative, is desigrlakd at 56. Output signals are generated from CCD array 58 as the negative 56 is scalmed. The output signals consist of tbree analog signals, one eæh for three primaries: red, green, and blue.
The output sigmals are ~,lu~ill~',y linear with respect to optical ~ ofthe negative being scarmed, in each color channel. The output of the sampling hardware is taken as mput to the digitization block 60, which consists of an adjustable analog gain stage 62 amd an analog-to-digital converter 64. The analog gain stage 62 allows adjustment of the signal input to the analog-to-digital converkr 64, which converts the arlalog signals to quantized digital signals having discrete levels. The output of the digitization stage can be directed to two modules, depending on the operational mode of the scanner. During preview mode, the output is directed to the input of a preview and cast correction module 72. Alternately, when m final scan mode, the output is direckd to the input of a color processor 74.

WO 96/3~291 ~ ~ ` PCI~/US96/04947 2l92lo4 A control line 90 and mode sv~itch 70 direct the signal from the analog-to-digital converter 64 toward the cast preview and removal module 72 or color processor 74based on the current selected scam mode. When scanner 32 is irl operation, the outputs of the cast preview and removal module 84, 86, and 88, Ic~ .ly, are directed to the light source 54, analog gam stage 62 and color processor 74, ~c*~.~Li~ly. In all three cases, the signals are gain or offset signals appropriate for adjusting the uullc~,ulldillg subsystems to achieve the desired cast removal. When in fmal scan mode, data from the analog-to-digital converter 64 are processed through the color processor 74 using mput from the cast preview and removal module 72 . The resultant image data can then be sent to a nulnber of outputs 76including host application 78 (e.g., Adobe Photoshop) running on the host computer 22, the color display monitor 80, or a storage file 8æ
Fig. 3 is a block diagram showing in more det il cast preview amd removal module 72. Input to module 72 is stored in digital memory 74. The contents of memory 74 can be read as r~put to three modules, depending ûn the mûde of operation of the cast preview and removal module 72. In the furst mode of operation, the cast predictions are determined by the cast prediction module 76, operating on the data in the preview memory buffer 74 and stored in a memory buffer 78 for later use. In a second amd optional mode, an exposure shift is computed by use of a scene amalysis module 92 operating on the contents of the preview buffer 74. The operation consists of creating a luminance signal from a color signal 94 and rulming the scene analysis processor 96. The output of processor 96 is a signal which isapplied equally to all three color channels, and will not intrûduce or remove a color cast.
Different cast prediction mPthn~ lo~i~c are carried out in block 76 and stored ,Li~,ly, blocks 80 or 82 or 84 or 86 in memory 78. The results ofthe cast prediction m~tht fl~ c are selectable by a selection mechanism 90 via operator intervention and the results are combined with the signal from the scene analysis module 92 at a junction 100. The combined signal is sent to a color processor 102 219210~
~WO 96/35291 ~, ~, PCINS96/04947 and/or to a gain ,u~uLiLiulfil~g module 106. The gain ~LiLiul~illg module 106, in turn, sends a signal to the light source 54, gain stage 62 and/or color processor 74.
In the tbird operational mode, the contents of the preview buffer 74 is processed through the color processor 102 with input from junction 100 and the resulting image displayed on color monitor 104 for cast judgment by the operator.
Cast prediction module 76 will now be described with reference to Fig. 4.
The contents of preview buffer 74 are p}ocessed through a color processor 200 to form a .~ ; , of scene exposure, which is stored in a memory buffer 202.
Cast operators 206, 208, 210 and 212 take the contents of this buffer as input, and each output a cast signal which is stored in a CUll-,~,UUlllliU~ memory buffer location 80,82,84,86, ~ ivcly, in the cast memory 78.
Fig. ~ shows a graphical user interface with which a user interacts in practicmg the invention. An operator interaction dialog 120 is used in the preferred ~ ., .1 .û.~l ", l It consists of a dialog box presented to the user on the color monitor 24 by computer 22. Region 122 is a color image display mto which is mapped the contents of the preview buffer 74 after processing by color processor 102 operating in the display mode of the cast preview and removal module 72. Below the previewis a cast selection mecharism 124 consisting of four buttons, 126,128,130,132, each ~ullc~luulldi~ to a cast memory location (80,82,84,86) in the cast buffer 78. Bdow the selection mechanism is a button for initiating a final scan 140, which sends imput to the mode switch 70. Region tool 142 allows the operator to select a region in the memory buffer 74 on which to perform the cast ~ u~ ull~ "uullliug to the enclosed region in the preview image 122 using the keyboard 26 or pomting device28.
The various color cast prediction m~thn~ c and their use will now be described. It will be seen that these comprise no cast prediction, whik point, gray world, and bright paskls. In general, the sequence of events in carrying out theinvention involve- (I) Color Cast Prediction with a low resolution scan, (2) Cast Selection, (3) Image Preview, and (4) Final Scan, which will now be described.
g wo 96135291 ~ PCr/USs6/04s 2~2~ ,. t-~
1. Color Cast Prediction A) Low resolution scan Referring to Figs. I and 2, scanner 32 is first configured for preview scanning. The gain of the analog gain stage 62 (a Imear amplifier) is set such that the rr~inimum density (film base density) for a negative of tbe selected film type produces an input signal to the amalog to digital converter 64 which is mapped to digit 1024 (out of 1024). Data for tbis adjustment is contained in a device profile for the sc~,,~ tive c~mh:-~tif)n selected by the user before initiating the sc~m. AsCCD 58 output voltage is nearly linear with respect to incident light, the digital counts from A/lD converter 64 will correspond to negative optical ~
The low resolution preview scan is made, and a resulting RGB I 0-bit image stored in the preview buffer 74 shown m Figure 3.
B) Low resolution image data conversion Using the ..l,-.,.... ;,, ~ ,.", for the ~ a~iY~ pair stored in the device profile,inthiscaseasetofonell;,l1 ,~;~",i~lLUTsrelatingscenelogexposureto10-bit digit for each channel: red, green, blue, the image data are converted from digital coumt to scene log exposure and stored in a computer memory buffer.
C) Cast prediction operators The following operations are performed on the log exposure data to predict candidate color casts.
I) None The first method is to perform no rnmrllt~ti~n and report a color cast of zero red, zero green amd ~ero blue exposure.
2) White Point The white point cast prediction method assumes that the brightest object in the scene is a specular reflection of the illllmin~fil-n source offa neutral object. The operation is performed in two parts -- isolation of the white, and .1. :. . ",;, ,~1 ;. ." of cast.
a) Isolating the white ~WO 96/35291 21 g 2 1 (~ 4 PCT/US96/04947 For every pixel location in the low-res image, compute the rninimum of the three exposure values at that location minRGB = Minimum(red,green,blue) and compare the value of minRGB to the highest of all previous minRGB.
maxMinRGB holds this value. Update it if necessary.
If(minRGB > maxMinRGB)then maxMinRGB = minRGB
b) Recording the cast If the brightness at the location is higher than all previous pixel locations fminRGB > maxMinRGB), save the exposure data for that pixel.
whitePt_red = red;
whitePt ~reen = green;
whitePt_blue = blue;
Repeat for every pixel.
3) Gray World The gray wo}ld cast prediction method is based on the o~plU~ iiUII that for a large number of scenes, the scene exposure in the tbree channels red, green, and blue when summed over the iInage area, will be equal. The operation is to simplydeterrnine the mean of all pixels in each of the three channels. That is:
Mean_Red = (nx * ny) ~ R~
Mean-Green=(nx*ny)~ Gy Mean_Blue= ( * )~ ~ ~^Y B,~
where Rij, Gij, Bij are the red, green, and blue exposures of the ij'th pixel, nx is the height of the selected region, and ny is the width, specified in low resolution pixels.

4) Bright Pastels The bright pastel cast prediction method is based on tne observation that a white point determmed from a specular highlight (as in the White Point method above) will be incorrect due to the object reflectance not being neutral. For example, -Il-red Christmas-tree ball might be the brightest oint found in the image, but ., ~,., P
certainly is not neutral and will cause a poor cast estimate. The bright pastel method operates by usimg the white point deter~nined above, and averages together all pixels v~rith exposure within a constant factor PASTELRANGE (e.g. ~) of the white having inter-chalmel color difference less th3n another factor (e.g. 0.15 logE) a) determine the exposure of the brightest pixel using the White Point method described above, then deter~nine the minimum brightness threshold.
minWhitePt = Minimum(whitePt_red,whitePt~reen whitePt_blue);
minbright = minWhitePt * I/PASTELRANGE;
b) reprocess the preview image, sumnung R, G, and B exposures separately for those pixels which are have brightness between the brightness threshold and the brightness of the white reference foumd m the image, and whichhave a pastel factor (Minimum(G-RG-B) ) less than the p~ct~ i7:1tinn threshold, and counting the number of pixels that meet this criteria After the entire low-resolution image has been processed, calculate the mean R, G, and B exposures which were included in the sums.
Once the cast exposures haYe been determined for each of the above methods, they are converted to balance offsets.
rBalance = ( GreenExp- RedExp) bBalance = ( GreenExp- BlueExp) and further modified to preserve luminance exposure level avg = ( rBalance + bBalance ) / 3, dExpRed = rBalance - avg;
dExpGreen = -avg;
dExpBlue = bBalance - avg;
The exposure changes to be applied to implement the cast removal are then:
newExpRed = OriginalExpRed + dExpRed newExpGreen = OriginalExpGreen + dExpGreen newExpBlue = Ori~in~lFxrFllue + dExpBlue ~W096/3~291 21~IO9 PC}/US96104947 II. Cast Selection M- ~' Once the cast prediction operation has concluded, and a set of candidate casts has been computed, the operator must select the preferred cast removal from the set of four ( three complex operations, and a null operation). A preferred method for fæilitating this selection is to generate an image preview from each of the fourcandidates -- which represents the fmal cast the operator will observe on the color monitor when the selected methods are applied to the final scan operation, regardless of how the cast-removal operation is actually i,..l,l. ,.,. ,t ~1 The preferred ~" ,l.o.l ,., .~ is to provide the user a set of "buttons" to select a cast (method) and update the color monitor rapidly to reflect the change in the image.
III. Ima~ePreview The color monitor used for the preview step must be adjusted prior to use such that the color of a neutral object in the scene (no color cast) has the appearance the user is attempting to achieve by the ~ udu-,Licll. In the preferred ~",1,.~1;".. l, the operator is assumed to have calibrated the display monitor in such a way that the Apple 13 inch Color Monitor device profile adequately represents the color monitor.
This calibration can be performed using readily available tools (e.g. Knoll Gamma tool supplied with Adobe Photoshop).
To preview the image, the contents of the preview buffer memory is processed tbrough the color processor using the ~ SdLiv~ profile appropriate for the negative currently being scanned. The profile ætually passed to the color processor has been modified to incorporate the cast change selected by the operator in the previous step (2 above). The resulting image is displayed on the color monitor for the operators judgment. This operation is repeated under the user control for all selections of cast (removal method).
IV. Final Scan Having selected the appropriate cast removal, the operator initiates a final scan. The scanner is reconfigured to pass the output(s) of the A/ D converter(s)directly to the color processor unit which has been configured as above to account WO 96/3~29~ T~ s 17 219210~
for the selected cast change. If the cast chamg~ is large, the change may be partitioned between the modified ~ ;aLivc profile and the analog gain stage ahead of the A/D converted to reduce data loss. A high-resolution scan is then made, processed through the color processor, and output to the host software ~rFlif~ti~n Those skilled in the r21evant aits will recogrlize that the invention may be T~ 1 in yet other ways according to its teachings. For example, in cu~ ,~iu~ ulu~a~Ly, lab negative printing equipment provides controls for color cast to a skilled operator, who manually determines and performs the cast adjustment. In many systems today, an automatic system has been ;~
consisting typically of a low-resolution electronic camera (stiL or video) whichur,~ ' the negative, performs a calculation on the resulting data, amd provides the result to the negative-printing system. Here, the present known cast correction ", 1, ~ could be replaced by the mvention.
The mvention may also be ;",1/l~ t ~1 in consumer camcorders or the like.
Consumer camcorders use a slightly different approæh, as the main problem is changing illuminant color ~ Jlc. Most operate by attempting to determine a white object in the scene, and then deriving color cast from the cast of the white point. The capture circuitry is then recalibrated "on-the-fly" as ,I.lllU~U~ ,Ull,y continues. (AGC-automatic gain control, amd auto white point control (corrects for difference m lighting color ~ UlC)) Color copiers may employ variations of the techniques described above.
Image-processing software allows user adjustment of color cast -- Adobe Photoshop "Variations" plug in for example. A user is given controls (R,G,B sliders for example) and can apply a specific cast change to an image.
In addition to the foregoing, other Gl ~ ~h~ may be ;. "1,~ "t ~1 and it is mtended that such r ~ ol~ be within the scope of the invention.

Claims (10)

What is claimed is:

1. Apparatus for predicting and correcting color cast errors in images in electronic form; said apparatus comprising:
means for acquiring an image in the form of an electronic signal;
means for transforming the signal into a standard color space;
display means for viewing images in standard color space coordinates;
means for predicting the color cast of said image using a plurality of color cast predictor methodologies and generating color correction signals for removing the color errors from said image with each of said methodologies; and means for selectively previewing said image on said display means with said color correction signals applied thereto and choosing one of them.

2. The apparatus of claim 1 further including a scanner for generating an image signal in electronic form.

3. The apparatus of claim 2 wherein said scanner is for reading transparencies and reflection media.

4. The apparatus of claim 2 further including gain adjustment means for adjusting the color balance and tone scale in said image signal.

5. The apparatus of claim 1 wherein said color cast predictor methodologies comprise white point, gray world, and bright pastel methodologies.

6. Apparatus for predicting and correcting color cast errors in images in electronic form; said apparatus comprising:
means for acquiring an image in the form of an electronic signal;
buffer means for storing at least a part of said image;
means for transforming the signal into a standard color space;
display means for viewing images in standard color space coordinates;
means for sampling the image to generate a low resolution version of at least a portion thereof;

means for predicting the color cast of said low resolution image using a plurality of color cast predictor methodologies and generating color correction signals for removing the color errors from said image with each of said methodologies.
means for storing each of said color correction signals;
means for selectively previewing said low resolution image on said display means with said color correction signals applied thereto and choosing one of them;
and means for correcting the entire image in accordance with a selected one of said color correction signals.

7. The apparatus of claim 6 further including a scanner for generating an image signal in electronic form.

8. The apparatus of claim 7 wherein said scanner is for reading and reflection media.

9. The apparatus of claim 7 further including gain adjustment means for adjusting the color balance and tone scale in said image signal.

10. The apparatus of claim 6 wherein said color cast predictor methodologies comprise white point, gray world, and bright pastel methodologies.