delivered the opinion of the court:
Following a bench trial, defendant, Bruce Nims, was found guilty of home invasion, rape, deviate sexual assault and armed robbery (Ill. *117Rev. Stat. 1981, ch. 38, pars. 12—11, 11—1, 11—3 and 18—2), and was sentenced to serve four concurrent terms of 25 years in the Illinois Department of Corrections. On appeal, defendant contends that he was not proved guilty beyond a reasonable doubt and that the State’s failure to comply with a discovery request deprived him of a fair trial.
Complainant testified that at 4 a.m. on August 15, 1981, she was asleep in the bedroom of her Chicago residence when she was awakened by the sound of a cigarette lighter clicking on and off. Defendant, who was holding the lighter in one hand and a knife in the other, warned her to keep quiet or he would cut her. He then raped complainant and forced her to perform an act of fellatio. Complainant testified that although the room was dark and she was not wearing her glasses, she was able to see defendant’s face because he was directly in front of her and the room was illuminated by light emanating from a side porch lamp and alley lights. She also stated that defendant lit a disposable cigarette lighter four or five times. Before leaving, defendant took complainant’s locket and chain, her purse and the disposable lighter and threatened to kill her if she told anyone what had happened.
Complainant reported the incident to the police as soon as defendant left and described him as a male black, 5 feet 9 inches to 5 feet 10 inches tall with brown skin, a light mustache and combed-back “permed” hair, wearing faded blue jeans and a navy-blue sweater. Before taking her to the hospital, the police drove her to a location four or five blocks away to view a suspect. Complainant stated that the suspect was not her assailant. At the hospital, she again described the offender and estimated his weight to be between 150 and 160 pounds. The following day, she viewed several books containing mug shots, but was unable to identify the attacker. Two days later, however, complainant identified defendant’s picture from an array of six photographs. She also was able to identify defendant in a lineup. Following complainant’s initial identification, the police recovered from defendant’s apartment a pair of blue jeans and a navy sweater which complainant identified as clothing worn by the offender. She recognized the blue jeans because they were faded and had zippers on the front.
Testifying for defendant, Officer Thomas Sheehan stated that complainant described the offender to his partner, Officer Colvin, as a male black, 5 feet 9 inches to 5 feet 10 inches tall who reeked of alcohol. The parties stipulated that in Colvin’s report of his interview with complainant, she also stated that her assailant was 18 to 20 years old, had a thin build and weighed approximately 150 pounds, *118and was wearing a blue or brown sweater and dark pants. Sheehan was not present when this information was conveyed to his partner. Colvin reported as “unknown” the description of the offender’s eyes, hair and complexion. Investigator Raymond Binkowski testified that he was given a description of the offender as a male black in his early twenties, with a medium-brown complexion, 5 feet 8 inches or 5 feet 9 inches tall, approximately 155 pounds and wearing a blue shirt or sweater. Binkowski received this description not directly from complainant but from another investigator who was preparing a composite description of a suspect wanted in a series of rapes.
Defendant then called an evidence technician who had processed the crime scene for physical evidence. Although the premises were dusted for fingerprints, the only prints discovered were smudged and unsuitable for comparison. Muddy footprints were found but the impressions were too light to photograph. Another evidence technician testified that tests performed on defendant’s clothing and shoes were negative for the presence of spermatozoa or blood. A soil comparison was impossible. At one point during defense counsel’s direct examination, the witness referred to a report he had compiled, causing defense counsel to state:
“Judge, just for the record, I just asked leave to mark a one page report as Defense Exhibit 2 for Identification. That is the first time to my knowledge that either myself or [co-counsel] has seen that report. We are prepared to proceed. I just wanted to make that known and tender a copy — or showing it to the State, who apparently has a copy.” (Emphasis added.)
Defendant testified that he is a 27-year-old black male weighing 179 pounds, approximately 5 feet 8 inches tall, and has worn a goatee for many years. Defendant stated that he has a scar over his left eye and what defense counsel described as a “knot” over his right eye as a result of injuries he sustained in a robbery that occurred in March 1980. Two other witnesses confirmed that defendant had the facial scars and wore the goatee prior to August 15, 1981. Defendant testified that at the time of the incident, he was playing cards with several friends, including Tyrone Parham, Ernest Bailey and Jim Conway. The game ended at approximately 6 a.m. Although Parham corroborated this testimony, he never advised the police of defendant’s whereabouts. Both defendant and his alibi witness had difficulty remembering the time, date and location of numerous other card games they had played in August 1981. Bailey and Conway did not testify although Conway was present at defendant’s trial.
Defendant initially contends that he was not proved guilty beyond a reasonable doubt because the testimony of complainant was neither clear and convincing nor corroborated by other evidence.
It is well established that the positive identification of a single witness is sufficient to support a conviction, provided that the witness is credible and observed the offender under conditions which would permit a positive identification to be made. (People v. Mendoza (1978), 62 Ill. App. 3d 609, 615-18, 378 N.E.2d 1318.) This is true even where the defendant presents alibi testimony which is corroborated by other witnesses. (People v. Shelby (1984), 123 Ill. App. 3d 153, 165, 462 N.E.2d 761.) Discrepancies or omissions in detail do not destroy the validity of an identification, but rather affect the weight of the testimony and are to be evaluated by the trier of fact. (People v. Shelby (1984), 123 Ill. App. 3d 153, 462 N.E.2d 761; People v. Mendoza (1978), 62 Ill. App. 3d 609, 378 N.E.2d 1318.) With regard to identification testimony, it has been noted that “untrained persons may give varying descriptions of another person’s physical characteristics” and that “an identification is not usually made by distinguishing separate features, but by the total impression made upon the witness.” People v. Shelby (1984), 123 Ill. App. 3d 153, 165, 462 N.E.2d 761.
In the instant case complainant testified that although it was dark in her bedroom, there was sufficient illumination from a side porch light and nearby alley lights to enable her to see defendant’s face. (She apparently was mistaken in her belief that light from a full moon was visible that night.) Additional illumination was provided by defendant’s action in lighting a disposable cigarette lighter. Although the dissent correctly notes that complainant was not wearing her glasses when she was attacked, it overlooks her testimony that the intruder forced her to look at him for approximately 20 minutes during which time his face was very close to her own. Complainant admitted that she is nearsighted but stated that even without her glasses she had “a clear view” of her assailant.
Both defendant and the dissent maintain that the description which complainant gave to the police did not match defendant’s actual physical appearance. We disagree.
Complainant described her assailant as a male black, 5 feet 9 inches to 5 feet 10 inches tall, weighing 150 to 160 pounds, with brown (or medium-brown) skin, a light mustache and combed-back *120“permed” hair. While defendant testified that he is 5 feet 8 inches tall and weighed 179 pounds, the trial judge could observe for himself whether defendant’s testimony regarding his height and weight was accurate. Moreover, defendant’s weight at trial had no necessary relationship to his weight at the time of the offenses one year earlier. Defendant did not dispute that he had a light mustache and combed-back “permed” hair in August 1981. Neither complainant nor any other witness testified that she had estimated the offender’s age. Investigator Binkowski was told by another investigator that the suspect who was wanted for a series of rapes, including this one, was in his early twenties. The parties stipulated, however, that complainant had told Officer Colvin that her assailant was 18 to 20 years old. In August 1981 defendant was 26 years old. In our judgment, the significance of this difference was a matter for the trial court to resolve.
The principal discrepancy between complainant’s description and defendant’s actual appearance concerns his facial scars and his goatee. Complainant did not mention these features when she was interviewed by the police. Although the photographs of defendant that were introduced into evidence1 do reveal a “knot” or bump above his right eye and a small scar above his left eye, the lighting conditions when these photographs were taken obviously were better than they were at the time of the crimes. With respect to defendant’s goatee, complainant did testify that her assailant had “a couple whiskers” on his chin but not “a beard.” As the dissent concedes, no chin hairs are apparent in any of defendant’s photographs. Complainant should not be faulted for not describing an invisible “goatee.” An examination of the photographs included in the supplemental record does reveal the *121presence of the “light mustache” to which complainant referred in her testimony.
As stated earlier, it is the total impression upon the witness rather than the distinguishing of separate features which generally forms the basis for an identification. (People v. Shelby (1984), 123 Ill. App. 3d 153, 164-65, 462 N.E.2d 761.) We agree with the trial court’s finding that the alleged discrepancies between complainant’s description of the offender and defendant’s actual physical appearance were minor in nature and did not affect her credibility as a witness. The court found that complainant “had sufficient opportunity to make that identification” and that “her identification was without question correct.” We will not disturb these findings.
The State introduced into evidence six photographs shown to complainant two days after she had been raped and one photograph of the four-man lineup conducted on the same day. The dissent waxes indignant over the State’s failure to have these photographs impounded at trial and made part of the record on appeal and speculates at length about their possible probative value. Curiously, defense counsel, particularly at oral argument, did not seem to be at all troubled by what has so exercised the dissent. Indeed, counsel opined that the photographs may not have captured all of defendant’s facial characteristics. In any event, we are unable to indulge in the conjecture offered by the dissent. Defendant is the appellant in this appeal and it was his responsibility to preserve evidence presented at trial. (People v. Wilson (1981), 92 Ill. App. 3d 370, 386, 415 N.E.2d 1315.) Had the photographs offered by the State possessed the evidentiary significance which the dissent attributes to them, surely defense counsel would have had them impounded and transmitted to this court as part of the record on appeal. At oral argument the assistant State’s Attorney acknowledged that the State has these photographs in its possession. Nevertheless, defendant has made no effort to obtain these photographs and file them as a supplemental record. Under these circumstances, the outrage expressed by the dissent over their absence clearly is gratuitous and misdirected.
Defendant also challenges as unduly suggestive the identification procedures utilized by the police. It appears that two days following the incident defendant was arrested on a disorderly conduct charge. While in custody a police officer noticed his physical similarity to the description given by complainant and included his picture in a photographic array presented to her. Complainant identified defendant’s photograph. Following this identification she was taken to the police station to view a lineup which included defendant. While at the sta*122tion she observed two photographs of defendant lying alongside the other five photographs which comprised the photographic array from which she had earlier identified him. Beneath defendant’s photograph was an arrest slip containing his name and other information. Complainant then viewed the lineup and identified defendant as well as certain clothing confiscated from his apartment.
In addressing defendant’s argument concerning the allegedly suggestive identification procedures, it is important to note that this is not a case in which the complaining witness made an identification from the first group of pictures shown to her. The record reveals that complainant viewed one suspect in person, then several books containing mug shots before finally identifying defendant’s picture in a photographic array. Moreover, the allegedly suggestive procedure of allowing defendant’s photograph, along with his arrest slip, to remain on a table within complainant’s view occurred after she had identified his picture as that of her attacker. Under these circumstances, we find that defendant was not prejudiced by the identification procedures employed in the instant case.
Both defendant and the dissent stress that his alibi defense was corroborated and unimpeached. It is well established, however, that the trier of fact is not required to believe alibi evidence even though it is unrefuted. (People v. Hunt (1980), 90 Ill. App. 3d 496, 501, 413 N.E.2d 215.) The value of alibi evidence necessarily hinges upon the credibility and believability of the witnesses providing the alibi, questions which are within the exclusive domain of the trier of fact. (People v. Hunt (1980), 90 Ill. App. 3d 496, 413 N.E.2d 215.) Here, the trial court specifically found that defendant and his alibi witness were not telling the truth. We note further that their testimony regarding other card games that they played in August 1981 was vague and that two other potential alibi witnesses did not testify even though the record indicates that one of them was present for defendant’s trial.
The dissent comments extensively regarding the lack of corroborative physical evidence in this case but ignores the reasons therefore. Although no evidence of spermatozoa or blood was discovered on defendant’s clothes or his shoes (there was no testimony that complainant had been cut), these items of clothing were recovered two days after the offenses were committed, allowing defendant ample time to remove any incriminating physical evidence. The fingerprints found at the scene were smudged and unsuitable for comparison. The impressions made by the offender’s shoes were too light to photograph and a soil comparison was impossible because defendant’s *123shoes had no dirt on them. Although none of complainant’s property was recovered, defendant’s apartment was not searched until two days after the offenses were committed. Defendant had more than adequate opportunity to dispose of the victim’s property. We note, however, that the police did recover from defendant’s apartment one pair of faded blue jeans with zippers on the front and a navy-blue sweater which complainant identified in court as clothing worn by her assailant.
Upon our review of the record, we are satisfied that defendant was proved guilty beyond a reasonable doubt.
Defendant next contends that he was deprived of a fair trial as a result of the State’s failure to provide him with a copy of an evidence technician’s report, as required by the discovery rules. 87 Ill. 2d R. 412.
Illinois law provides that upon learning of an alleged nondisclosure, defendant must take affirmative action by seeking a continuance or by requesting appropriate sanctions and cannot wait until after the trial and verdict to complain. (People v. Rogers (1984), 122 Ill. App. 3d 384, 393, 461 N.E.2d 511.) In the absence of such affirmative action, the defendant will be found to have waived his objections to the nondisclosure. (122 Ill. App. 3d 384, 461 N.E.2d 511.) Furthermore, the State’s noncompliance with a discovery requirement does not warrant reversal absent a showing of prejudice. (People v. Velez (1984), 123 Ill. App. 3d 210, 219, 462 N.E.2d 746.) In People v. Foster (1979), 76 Ill. 2d 365, 384, 392 N.E.2d 6, the Illinois Supreme Court stated that a defendant’s failure to request a continuance or recess when confronted with a discovery violation is persuasive evidence that any alleged prejudice was in fact trivial.
In the instant case, the evidence technician who compiled the report was called as a defense witness and was examined thoroughly concerning the contents of the report. Although defense counsel noted “for the record” that neither he nor co-counsel previously had seen the report, he informed the court that “we are ready to proceed.” With the above-stated principles in mind, we do not believe that reversal is warranted under these circumstances.
For the foregoing reasons, the judgment of the circuit court of Cook County is affirmed. Pursuant to People v. Nicholls (1978), 71 Ill. 2d 166, 374 N.E.2d 194, we grant the State’s request that defendant be assessed $50 as costs for the State’s defending this appeal and incorporate it as part of our judgment.